Frequently Asked Questions

Red blood cells

Kidney disease

No. Normal complement concentrations do not exclude aHUS because low levels of circulating C3 have low sensitivity (about 30% of patients with aHUS), whereas high concentrations of circulating C5a and soluble C5b-9 might have insufficient specificity.

Learn more here.

Yes, vitamin B12 is synthesized solely by microorganisms (ruminants obtain Cbl from the foregut) and is naturally present in foods of animal origin, including fish, meat, poultry, eggs, and dairy products. In addition, fortified breakfast cereals and fortified nutritional yeasts are readily available sources of vitamin B12 that have high bioavailability. The bioavailability of vitamin B12 is about three times higher in dairy products than in meat, fish, and poultry, and the bioavailability of vitamin B12 from dietary supplements is about 50% higher than that from food sources. Vegans are at increased risk for developing vitamin B12 deficiency. Read more here.

*DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin B12 is 2.4 mcg for adults and children aged 4 years and older [21]. FDA does not require food labels to list vitamin B12 content unless vitamin B12 has been added to the food. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. From NIH.


Yes. In some centers, the DAT (direct antiglobulin test) has largely replaced the term Coombs test. Coombs test was named after Robin Coombs, a British immunologist who developed the principle behind the antiglobulin test while travelling back to Cambridge on a wartime train.

Yes. Learn more here.

Acute attacks are very rare before puberty and after menopause, with a peak occurrence within the third decade. They are more common in women than in men. Most patients have one or a few attacks and then recover fully for the rest of their lives.

Learn more here.

Fragmented RBCs can be detected by certain automated hematology analyzers based on the analysis of fraction of small red blood cells (RBCs) in the context of normal RBC volume indices (mean corpuscular volume and width). Their presence should prompt a peripheral blood smear review.

Figure: A specific area below the RBC area in the RET scattergram is used for identification of fragmented red blood cells. Due to the absence of nucleic acids in red blood cells the intensity of the measured side fluorescence signals (SFL) is extremely low. In addition, the high-angle forward scatter (FSC) is lower than that of intact red blood cells. Each cell is plotted in the RET scattergram based on its fluorescence intensity (SFL on x-axis) and its high-angle forward scatter (FSC on y-axis), which reflects characteristics of both cell size and cellular content. The triangle indicates the detection area for fragmented red blood cells (FRC). Source.

Rarely, haptoglobin (Hp) levels are normal or increased in hemolysis owing to inhibition of the macrophage uptake of the haptoglobin-hemoglobin complex (Hp-Hb) by the CD163 receptor.

Hb, hemoglobin; Hp, haptoglobin; liver, upper left; lysed red cell, upper right; macrophage, bottom.

Yes! AABB states that a single unit RBC transfusion should be standard in nonbleeding, hospitalized patients and additional units prescribed only after reassessment of patient and hemoglobin (Hb) level.

Food and Drug Administration (FDA) regulations permit hemochromatosis patients to donate blood, provided the donor (the hemochromatosis subject) meets standard blood donor eligibility criteria.

The American Red Cross does not permit hemochromatosis patients to donate blood because it “has a long-standing policy that potential donors are not allowed to receive direct compensation for their donation (beyond the usual orange juice and cookie). Because people with hemochromatosis would otherwise have to pay for their therapeutic phlebotomies, they would in effect be getting something of value for being able to donate for free. Thus the Red Cross has ruled that such donations violate their policy” (read more here).

Bottom line: blood-collection organizations can determine their own protocols within U.S. Food and Drug Administration regulations, which stipulate acceptable iron levels in donated blood.

In a 2016 Editorial, West and Eder wrote:

Safety concerns historically stem from the possibility of creating an incentive to donate blood for free rather than to pay for therapeutic phlebotomy, possibly encouraging HH donors to deny risk factors for infectious diseases. In the Final Rule that became effective in May 2016, the US Food and Drug Administration codified the requirements for hereditary hemochromatosis (HH) donors in the Code of Federal Regulations (CFR), thus eliminating the need for a variance to collect whole blood more frequently than every 8 weeks (or double red blood cells more frequently than every 16 weeks) and distribute units without special labeling from HH donors who meet all eligibility requirements. Notably, the CFR retains the requirement for obtaining a prescription for therapeutic phlebotomy from a licensed health care provider and performing therapeutic phlebotomy free of charge… Since the molecular basis of the disease was elucidated in 1996, it has been posited that the condition itself poses no harm to the recipient. The question concerns the motives of the HH donor to give blood and the possibility of incentive to withhold information from blood establishments about infectious risk factors

In 2016, the American Red Cross wrote (despite its continued refusal to allow patients with HH to donate blood) a piece titled “Iron-rich blood is just fine, thank you!”:

For decades, blood centers in the United States would not collect whole blood from donors/patients with hereditary hemochromatosis (HH), in some cases because it used to be that such units had to be labeled with the disease necessitating its removal… In 2016, the FDA encoded the regulations for therapeutic phlebotomy… Special labeling is not required, and units may be distributed if they meet regular requirements and criteria, as long as the therapeutic phlebotomy (TP) is ordered by a physician and the phlebotomy performed without charge.

Rarely, owing to skewed X chromosome inactivation.

Thrombocytopenia is absent at presentation in 15–20% of patients.

Learn more here.

Skin lesions never develop in acute intermittent porphyria, but are the only clinical manifestation in some patients with variegate porphyria (60% of patients), and rarely (5%) develop in patients with hereditary coprophorphyria. Learn more here.

Yes, G6PD seems to be protective, as are many of the hemoglobinopathies and ethnic neutropenia. Learn more about hemoglobinopathies and malarial infection here.

SE, South East; HS, hereditary stomatocytosis

nRBCs are typically enumerated by one of the following methods:

  • Manual counting of Wright-Giemsa-stained peripheral smears:
    • Part of the traditional 100-cell manual differential leukocyte count.
    • Reported as number of nRBCs per 100 white blood cells (WBCs).
  • Automated hematology analyzers (for example, Sysmex)
    • Reported as relative number of nRBCs per 100 WBCs or as an absolute number.
Cool schematic of nucleated red cell from Sysmex.
Wright-Giemsa-stained peripheral blood smear showing nucleated red blood cell in center of field.
Counting nucleated red cells in an automated cell counter. In the WNR Channel, the analyzer measures side fluorescence and forward scatter. Side fluorescence measures the nucleic acid content to identify NRBCs in the same channel in which white cells are counted. Forward scatter measures cell size. WNR, white count and nucleated red blood cells. Source.

Porphyrias may be classified:

  • According to the organ in which heme precursors accumulate:
    • Hepatic
    • Erythropoietic
  • According to clinical presentation:
    • Acute porphyrias
    • Cutaneous porphyrias
    • Rare recessive porphyrias

Learn more here.

1) Reticulocyte stain:

The traditional method of measuring the reticulocyte count is a manual method that uses supravital stains (such as methylene blue) to highlight the reticulum (RNA) network of this immature red cell fraction. A lab technologist uses a microscope to count the number of such cells relative to the number of mature red blood cells. The number of reticulocytes is reported as a percentage of total red blood cells.

Reticulocyte stain in which living red blood cells are incubated in methylene blue. reticulocytes are readily identified by the presence of a network of reticular material.

2) Automated analyzer:

The number of reticulocytes can be measured directly by most automated analyzers by staining the remnant RNA with a fluorescent dye. The number of reticulocytes is reported as an absolute count.

Scattergram of the reticulocyte (RET) channel with a normal cell distribution. In the RET channel, the lysis reagent slightly perforates the cell membranes of red blood cells, white blood cells and platelets and so allows the fluorescence marker to penetrate the cell. The fluorescence marker labels the intracellular nucleic acids whereby the intensity of the resulting fluorescence signal is directly proportional to the nucleic acid content. Using the forward scattered light and the fluorescence signal, the reticulocytes can be separated from mature red blood cells. Source.

About one-half of patients with sickle cell disease have chronic ophthalmologic complications.

30%-70% of patients develop side effects, including:

  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Epigastric pain
  • Metallic taste

Anemia occurs in about 75% of patients with chronic liver disease.

Learn more here.

Prevalence is 25-30%.

Prevalence is 10%-40% in adults with sickle cell disease (less common in children).

Thrombocytosis occurs in about 10-15% of patients with iron deficiency anemia. Learn more here.

Absolute vitamin B12 deficiency occurs in up to 6% of those aged 60 years and older. Learn more here.

If Hct > 54%, either reduce or stop testosterone therapy or initiate phlebotomy while continuing testosterone therapy.

Let’s look at the clinical practice guidelines:

2017 British Society for Sexual Medicine Guidelines on Adult Testosterone Deficiency, With Statements for UK Practice:

J Sex Med. 2017;14:1504-1523.

2018 Evaluation and Management of Testosterone Deficiency: AUA Guideline:

J Urol. 2018;200:423-432.

Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline:

Erythrocytosis = hematocrit > 54%.

Glucose indirectly inhibits aminolevulinic acid (ALA) synthase activity and thereby decreases overproduction of ALA and porphobilinogen (PBG).

Hemin (available in the United States as Panhematin) suppresses aminolevulinic acid (ALA) synthase activity and thereby decreases overproduction of ALA and porphobilinogen (PBG).

Leukocyte reduction filters are used to remove > 99.9% of leukocytes. According to a Circular of Information from the AABB, American Red Cross, America’s Blood Centers, and the Armed Services Blood Program, leukocyte-reduced units of red blood cells must have a residual content of leukocytes <5.0 x 106.

About 70% of patients with pernicious anemia have macrocytosis. Learn more here.

Small clinically silent PNH clones are found in up to 70% of adults. Learn more here.

Reduction in hemoglobin ≥ 2 g/dL (20 g/L) below baseline (per NIH 2014 clinical practice guideline).

Two main classification schemes:

  • Based on reticulocyte count (hypoproliferative vs. hyperproliferative)
  • Based on red cell morphology (microcytic [with or without hypochromia]) vs. normocytic vs. macrocytic)
MCV, mean cell volume; BM, bone marrow; HA, hemolytic anemia; TMA, thrombotic microangiopathy; MAHA, microangiopathic hemolytic anemia; SCD, sickle cell disease; HS, hereditary spherocytosis; HE, hereditary elliptocytosis; PNH, paroxysmal nocturnal hemoglobinuria; PKD, pyruvate kinase deficiency.

Elevated urine porphobilinogen (PBG) confirms diagnosis in acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), or variegate porphyria (VP). PBG level is normal in the very rare ALA dehydratase deficiency porphyria (ADP). Discriminating between AIP, HCP, and VP requires additional testing.

Heme biosynthesis pathways showing the 4 enzymes (in red) responsible for acute porphyria.
  • Absolute erythrocytosis (elevated red blood cell mass)
    • Primary – cause is intrinsic to the red blood cell
    • Secondary – cause is extrinsic to the red blood cell
  • Apparent or relative erythrocytosis (reduced plasma volume relative to red blood cell mass).
P. vera, polycythemia vera; ODC, oxygen dissociation curve; R-L shunt, right to left shunt; EPO, erythropoietin.

Learn more here.

Urine dipstick positive for blood + urine microscopy negative for red cells is consistent with hemoglobinuria or myoglobinuria. Differentiating between hemoglobinuria and myoglobinuria is usually obvious based on the clinical context (for example, serum hemolytic indices positive in hemoglobinuria and serum CK elevated in myoglobinuria), but definitive diagnosis can be made using mass spectrometry.

Learn more here.

  • Presence of elliptocytes on peripheral blood smear (fragmented red blood cells may also be seen).
  • Increased osmotic fragility.
  • Osmotic gradient ektacytometry shows characteristic deformability profiles with curve exhibiting a trapezoidal form with a decrease in the RBC deformability.
  • DNA testing panels can define the pathogenic mutations in alpha-spectrin, beta-spectrin, and protein 4.1 in HE.

International Council for Standardization in Haematology (ICSH) guidelines one laboratory diagnosis of nonimmune hereditary red cell membrane disorders:

Osmotic deformability profiles of red cells from normal control and HE. HE is characterized by a trapezoidal curve with moderately decreased IDmax but normal Omin and Ohyper results.

Learn more here.

  • Presence of spherocytes on peripheral blood smear
  • Increased mean corpuscular hemoglobin concentration (MCHC) (> 36 g/dL [360 g/L])
  • Increased lysis in osmotic fragility test and reduced fluorescence signal in eosin-5-maleimide (EMA) binding test

Diagnosis of HS does not necessarily require molecular analysis of affected genes.

2012 British Committee Standards in Haematology (BCSH) expert guideline on diagnosis of hereditary spherocytosis recommendations:

Flow cytometry using ≥ 2 different monoclonal antibodies against 2 different glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) on ≥ 2 different blood cell lineages. Learn more here.

Pica is defined as the compulsive eating of non-nutritive substances. Learn more here.

  • Primary (idiopathic)
  • Secondary – associated with presence of other disorders, including iron deficiency

Learn more here.

By dividing the hematocrit (Hct) by the red blood cell count (RBC):


For example:
45% = 5 x 1012/L x 90 x 10-15L

  • Mild HS
    • Normal Hb level with reticulocytes < 6%.
    • May require 0-1 transfusion during lifetime and rarely splenectomy.
  • Moderate HS
    • Hb level > 8 g/dL (80 g/L) with reticulocytes 6%-10%.
    • May require 0-2 transfusions during infancy and in some cases splenectomy (if the capacity level is decreased).
  • Moderately severe HS
    • Hb level 6-8 g/dL (60-80 g/L) with reticulocytes > 10%.
    • May require > 2 transfusions intermittently and splenectomy likely necessary.
  • Severe HS
    • Hb level 10%.
    • Require regular transfusions and splenectomy likely necessary.

2012 British Committee Standards in Haematology (BCSH) expert guideline on diagnosis of hereditary spherocytosis:

Learn more here.

  • 21 days if stored in citrate phosphate dextrose (CPD), or CPD2 anticoagulant-preservative
  • 35 days if stored in citrate phosphate dextrose adenine 1 (CPDA-1)
  • 42 days using current generation of additive solutions additive solutions

Most acute attacks last for no longer than 1 or 2 weeks.

Learn more here.

Continue oral iron for 3-6 months after the iron deficiency has been corrected in order to replenish iron stores.

About 4,500

Ferritin Structure: Apoferritin forms a roughly spherical container within which ferric iron is stored as a ferrihydrite mineral. Apoferritin refers to the iron-free form of the protein; the iron-containing form is termed holoferritin or simply ferritin. The apoferritin shell is composed of 24 subunits of two types, termed H and L, the ratio of which varies widely depending on tissue type and inflammation. Iron is toxic in cellular systems because of its capacity to generate reactive species (shown as yellow spheres) which can directly damage DNA and proteins. From Knovich et al.
ferritin structure
Ferritin is a hollow protein shell composed of 24 subunits. Two subunits have been removed to allow visualization within the core where up to 4500 iron atoms can be stored. Source

> 1000! Learn more here.

100 million per year worldwide, 13 million in the US.

About 2 x 1011 (200 billion) or 1% of all red cells

About 200 × 109 per day

There are 8 enzymes in the heme biosynthesis pathway. Mutations in each enzyme can cause porphyria. Therefore there are 8 different kinds of porphyria.

Heme biosynthesis pathway

1-2 mg is derived from intestinal absorption.

Each unit of RBCs (processed from 420 mL of donor blood) contains about 200 mg of iron (0.47 mg iron/mL of whole donor blood or 1.08 mg iron/mL of pure RBCs).

The human body normally contains 40 to 50 mg/kg of iron, which amounts to 3-4 grams. It is distributed in the following compartments:

  • Hemoglobin in RBCs – about 30 mg/kg
  • Myoglobin in muscle – about 4 mg/kg
  • Iron-containing enzymes – about 2 mg/kg
  • Storage in ferritin and hemosiderin – 0-2,000 mg
  • Plasma transferrin – 1-2 mg

About 25 mg of iron daily (far more than the 1 mg that is absorbed by the gastrointestinal track).

25-40% larger; mean cell volume about 120 fL, though quite variable. Learn more here.

About 1%. This route of absorption is unaffected in patients with pernicious anemia, and is the rational for oral vitamin B12 therapy. Learn more here.

About 10%-20% of cases remain unexplained.

Hemoglobin typically increases by 20 g/L at 2 weeks, with a normal hemoglobin level usually achieved in 2 months. Ferritin may take up to 6 months to return to normal.

Historically, doses of elemental iron as high as 100–200 mg per day across two to three divided doses were recommended. However, it is now recognized that a dose of iron will increase hepcidin levels, which will then inhibit the absorption of the next dose. Iron absorption is most efficient with intermediate doses and on alternate days, and this approach is recommended in patients with mild symptoms, or no or mild anaemia.

Up-to-Date recommendations:

  • We typically advise our patients to take their dose every other day as long as they can manage the schedule appropriately; a reasonable variation on the schedule that is easier to follow is to give the dose on Monday, Wednesday, and Friday.
  • There is no reason to give more than one dose per day.
  • The amount of iron in the every-other-day dose or the Monday-Wednesday-Friday dose is also not well established. However, there is not a reason to think higher doses improve absorption, and adverse effects are generally dose related. Thus, we typically use one tablet per dose (e.g. 325 mg ferrous sulfate). 

2021 British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults:

Learn more here.

Learn more here.


IV carbohydrate loading has potential risk of hyponatremia, which can lead to cerebral edema.

According to the British Society of Haematology:

  • Hct > 52% in men persisting for > 2 months
  • Hct > 48% in women persisting for > 2 months

No, it must be ordered separately.

Women have a higher prevalence compared to men.

Learn more here.

Yes, and this is the justification for periodic surveillance endoscopies in these patients. Learn more here.

Yes. Vitamin B12 refers to a specific group of cobalt-containing corrinoids with biological activity in humans. This group of corrinoids is also referred to as cobalamins. The main cobalamins in humans and animals are adenosylCbl, methylCbl, and hydroxoCbl. Food Cbl is hydroxoCbl. Cyanocobalamin is a synthetic form of vitamin B12 found only in supplements. Learn more here.

Yes, typically for complement only. However, it is also weakly positive for IgG in about one quarter of cases. Learn more here.

X-linked. Learn more here.

No, about 30% of cases occur in patients without anemia. This is called isolated macrocytosis.

Oral vitamin B12 replacement at 1000 μg daily is an adequate alternative to IM B12 injections. Learn more here.

No, it is also seen in preadolescents and during pregnancy (more common at the beginning of pregnancy than in late pregnancy). Learn more here.

Yes, on both venous and arterial sides of the circulation. Learn more here.

Serum erythropoietin is low in about 90% of patients with polycythemia vera. Learn more here.

Retinopathy has been reported in 70% of patients with HbSC compared with about 45% in sickle cell anemia. Learn more here.

No. It is also seen in:

  • Pregnancy
  • Chronic kidney failure
  • Major depressive disorder
  • Generalized anxiety disorder
  • Panic disorder
  • Attention-deficit/hyperactivity disorder

Read more here.

No. Serum iron levels are highly dependent on recent food intake and they follow a diurnal rhythm (though there is no evidence that fasting samples perform better than random samples). Learn more here.

There is no strong evidence for plasma therapy efficacy in atypical hemolytic uremic syndrome.

Learn more here.

No. Learn more here.

1-5 mg/day

According to DailyMed: Daily doses greater than 1 mg do not enhance the hematologic effect, and most of the excess is excreted unchanged in the urine. The usual therapeutic dosage in adults and children (regardless of age) is up to 1 mg daily. Resistant cases may require larger doses.

Guidance varies by professional organization.

2021 AGA clinical practice guidelines on the gastrointestinal evaluation of iron deficiency anemia:

2021 British Society of Gastroenterology (BSG) guideline on management of iron deficiency:

Hemoglobin (Hb) and hematocrit (Hct). Hct correlates a little better with red cell mass compared with Hb (learn more here).

Depends on the clinical context. In patients with anemia, we should refer to the Hb because oxygen carrying capacity is limiting, whereas the Hct should be considered in those with polycythemia since blood viscosity is limiting. For those with normal Hb/Hct, both oxygen carrying capacity and blood viscosity are at equipoise, so take your choice!

2021 AGA Clinical Practice Update on the Diagnosis and Management of Atrophic Gastritis (AG): Expert Review:

Providers should consider performing endoscopic surveillance every 3 years in patients with advanced AG. However, it should be recognized that optimal surveillance intervals remain to be determined, and shorter or longer intervals may be appropriate depending on individual risk assessment.

Learn more here.

2020 AGA Clinical Practice Guidelines on the Gastrointestinal Evaluation of Iron Deficiency Anemia:

2021 British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults:

The RDW-CV (RDW coefficient of variation) is inversely proportional to the mean cell volume (MCV). As a result, patients with microcytosis have elevated RDW-CV regardless of variation in cell size, while those with macrocytosis have lower RDW-CD values. By contrast, the RDW-SD (RDW standard deviation) is not influenced by the MCV and therefore may be preferable to use. An RDW-SD > 46 fL represents anisocytosis.

Hydroxyurea (since 1998), L-glutamine, crizanlizumab, voxelotor

  • Acute hemolytic transfusion reaction (AHTR)
  • Febrile nonhemolytic transfusion reactions (FNHTR)
  • Urticaria
  • Anaphylaxis
  • Transfusion-related acute lung injury (TRALI)
  • Transfusion-associated circulatory overload (TACO)
  • Nonimmune hemolysis
  • Hypotensive transfusion reactions
  • Transfusion-associated sepsis

Blood loss, hemolysis, erythropoietin administration, high altitude

  • Hemorrhage +/- iron deficiency
  • Hypersplenism
  • Alcohol
  • Bone marrow failure and aplastic anemia develop after an episode of hepatitis
  • Complication of treatment of chronic hepatitis C
  • Spur cell anemia

Learn more here.

Learn more here.

  • Changes in hemoglobin oxygen affinity, for example high-affinity hemoglobin mutations.
  • Mutations in oxygen sensing/hypoxia-inducible factor (HIF) signaling pathway, for example Chuvash polycythemia (mutation in VHL gene, automosomal recessive).

Learn more here


  • Congenital (erythropoietin receptor mutations)
  • Polycythemia vera
  • Idiopathic erythrocytosis


  • Congenital
    • Defects in oxygen sensing pathway – Chuvash erythrocytosis (VHL mutation)
    • Left shift of hemoglobin (Hb) oxygen dissociation curve:
      • High affinity Hb
      • 2,3-DPG deficiency
  • Acquired
    • Hypoxia-driven:
      • Central process:
        • Chronic lung disease
        • Right-to-left cardiopulmonary shunts
        • Carbon monoxide poisoning
        • Smoking
        • Sleep apnea
        • High altitude
      • Local process:
        • Renal artery stenosis
        • Hydronephrosis
        • Renal cysts
    • Pathological erythropoietin production:
      • Tumors:
        • Hepatocellular carcinoma
        • Renal cell cancer
        • Cerebellar hemangioblastoma
        • Uterine leiomyoma
        • Pheochromocytoma
        • Meningioma
    • Drug-associated:
      • Erythropoietin
      • Androgens
      • Diuretics
Epo, erythropoietin; ODC, oxygen dissociation curve; R-L shunts, right-to-left shunts; CO, carbon monoxide; P. vera, polycythemia vera.

Learn more here.

Broad overview of anemia, showing causes of hemolytic anemia. TMA, thrombotic microangiopathy; MAHA, macroangiopathic hemolytic anemia; SCD, sickle cell disease; HS, hereditary spherocytosis; HE, hereditary elliptocytosis; PNH, paroxysmal nocturnal hemoglobinuria; PKD, pyruvate kinase deficiency.
First branchpoint in diagnostic algorithm is immune vs. non-immune hemolysis. Virtually all cases of immune-mediated hemolysis (whether alloimmune or autoimmune) will be associated with a positive direct antiglobulin test (DAT) (Coombs test).
If the DAT is negative, the differential diagnosis includes extracorpuscular and intracorpuscular non-immune conditions. Extracorpuscular causes are those in which the red cells are innocent bystanders, reacting to changes in their extracellular environment. Intracorpuscular causes are those that are inherent in the red cell itself.
Intracorpuscular causes of hemolysis involve three broad categories: defects in hemoglobin, membrane or enzymes. The hemoglobin ‘bucket’ includes thalassemia and sickle cell disease; membrane causes include hereditary spherocytosis, hereditary elliptocytosis and hereditary stomatocytosis, and paroxysmal nocturnal hemoglobinuria (PNH; the only acquired condition in the intracorpuscular category); and defects in enzymes causing hemolysis include G6PD and pyruvate kinase deficiencies.
On the extracorpuscular side are conditions associated with thrombotic microangiopathy, including primary and secondary thrombotic thrombocytopenia purpura (TTP) and hemolytic uremic syndrome (HUS), and disseminated intravascular coagulation (DIC); and a series of non-TMA causes (“other”) including burns/thermal injury, microangiopathic hemolytic anemia from prosthetic valves or foot strike anemia, Clostridial sepsis, Wilson’s disease and spur cell anemia.

Nucleated red blood cells are a reflection of extreme increases in erythropoietic activity as seen in/with:

  • Hemoglobinopathies
  • Brisk hemolysis
  • Rapid blood loss
  • Other conditions of hematopoietic stress such as sepsis
  • Damage or stress to bone marrow, for example in:
    • Chronic myeloid leukemia
    • Acute leukemia
    • Myelodysplastic syndromes
  • Chemotherapy
  • Myelophthisic conditions, including:
    • Metastatic cancer to bone marrow
    • Bone marrow fibrosis
GI, gastrointestinal; GU, genitourinary; IV, intravascular.

Learn more here.

Lactate dehydrogenase (LDH), indirect (unconjugated) bilirubin, haptoglobin, and AST. Learn more here.

Hemolysis is associated with elevated serum levels of leakage products, LDH and AST; reduced levels of haptoglobin (Hp) owing to binding to free Hb and internalization in macrophages (without recycling); and elevation of unconjugated (indirect) bilirubin from breakdown of heme inside macrophages.
  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Epigastric pain
  • Metallic taste

Large precipitates of denatured hemoglobin often seen in patients with G6PD deficiency and hemolysis. Requires special stain of blood using methyl violet. See images.

  • Those at risk for transfusion-associated graft-versus-host disease (TA-GVHD) caused by proliferation of donor T lymphocytes
  • Those who are immunocompromised
  • Those receiving intrauterine transfusion
  • Those with hematologic malignancies or solid tumors, including:
    • Sarcoma
    • Neuroblastoma
    • Hodgkin lymphoma
  • Those who are recipients of marrow or peripheral blood stem cell transplantation
  • Those receiving RBCs from blood relatives or human leukocyte antigen-compatible donors
  • Those receiving fludarabine therapy
  • Those receiving granulocyte transfusions

According to the AABB:


  • Blood components that contain viable lymphocytes may be irradiated to prevent proliferation of T lymphocytes, which is the immediate cause of TA-GVHD.
  • Irradiated blood is prepared by exposing the component to a radiation source.
  • The standard dose of gamma or X-ray irradiation is 2500 centigray (cGy) targeted to the central portion of the container with a minimum dose of 1500 cGy delivered to any part of the component.


  • Patients at risk for TAGVHD, including:
    • Fetal and neonatal recipients of intrauterine transfusions
    • Selected immunocompromised recipients
    • Recipients of cellular components known to be from a blood relative
    • Recipients who have undergone peripheral blood progenitor cell transplantation
    • Recipients of cellular components whose donor is selected for HLA compatibility and recipients of granulocyte transfusions.
    • Patients receiving purine analogues (eg, fludarabine, cladribine) or certain other biological immunomodulators (eg, alemtuzumab, antithymocyte globulin) who may be at risk for TA-GVHD, depending on clinical factors and the source of the biological agent.
  • Symptomatic hemolytic anemia
  • Presence of gallstones
  • Large reduction in exercise tolerance
  • Growth retardation
  • Skeletal changes or leg ulcers due to HS
  • Extramedullary hematopoietic tumors
  • Vascular compromise of vital organs in older patients
  • Splenic infarct with pain or early satiety from splenomegaly

Consider delaying splenectomy until > 6 years old if possible.

Guideline recommendations:

Recommendations regarding splenectomy in hereditary hemolytic anemias by Splenectomy in Rare Anemias Study Group (2017):

2012 British Committee Standards in Haematology (BCSH) expert guideline on diagnosis of hereditary spherocytosis:

Patients should be selected for splenectomy on the basis of their clinical symptoms and presence of complications such as gallstones, not simply on the basis of the diagnosis alone (grade 2 recommendation, grade C evidence). Splenectomy should be performed in children with severe HS, considered in those who have moderate disease, and should probably not be performed in those with mild disease. A careful history is important in those with moderate to mild disease to establish if there is evidence suggesting reduced exercise tolerance; the metabolic burden of increased marrow turnover may be considerable. Where there is a family history, the benefit of splenectomy in other individuals may help determine whether to proceed.
  • Patients intolerant or not responding to oral iron.
  • When there is a need for a quick recovery in patients with iron deficiency anemia.
  • Patients taking erythropoiesis stimulating agent (ESA), for example those with anemia of chronic kidney disease.
  • Patients with inflammatory bowel disease inflammatory bowel disease and iron deficiency anemia.
  • Patients with history of severe allergic reactions to plasma-containing products.
  • Patients who have absolute immunoglobulin A (IgA) deficiency and for whom no IgA-deficient RBCs are available.
  • Patients at risk of hyperkalemia.
  • Neonates with neonatal alloimmune thrombocytopenia requiring maternal RBC transfusion that contains antihuman platelet antigen-1a (however, use of washed RBCs is not required.)

According to AABB:

  • Description:
    • Washed components are typically prepared using 0.9% Sodium Chloride, Injection USP with or without small amounts of dextrose.
    • Washing removes unwanted plasma proteins, including antibodies and glycerol from previously frozen units.
    • The shelf life of washed components is no more than 24 hours at 1 to 6 C or 4 hours at 20 to 24 C.
    • Washing is not a substitute for leukocyte reduction, and only cellular components should be washed.
  • Indications:
    • To reduce exposure to antibodies targeting known recipient antigens.
    • To remove constituents that predispose patients to significant or repeated transfusion reactions (eg, removal of IgA-containing plasma in providing transfusion support for an IgA-deficient recipient or in rare recipients experiencing anaphylactoid/anaphylactic reactions to other plasma components).

Less avascular necrosis, pulmonary hypertension, leg ulcers, and stroke; more retinopathy. 0.4% painful crises per patient year in those with HbSC, less than half the rate in sickle cell anemia. Learn more here.

Avascular necrosis++++
Pulmonary hypertension++++
Leg ulcers++++
Painful crises ++++

Conditions associated with:

  • Appropriate release of erythropoietin from oxygen sensing cells in the kidney, including:
    • Cardiopulmonary disease
    • High altitude
    • Hereditary hemoglobin mutations associated with high oxygen affinity
  • Inappropriate release of erythropoietin from:
    • Oxygen sensing cells in the kidney, including renal disorders and drugs
    • Tumor cells
P. vera, polycythemia vera; ODC, oxygen dissociation curve; R-L shunt, right to left shunt; EPO, erythropoietin.

See additional list of causes from PMC7829024. Learn more here.

Other clinical manifestations of iron deficiency per se include dizziness, tinnitus and reduced concentration.
  • Neurological symptoms
  • Pancreato-intestinal involvement
  • Gangrene of the fingers or toes
  • Ulcerative–necrotic skin lesions
  • Myocardial infarction
  • Ischemic cardiomyopathy

Learn more here.

  • Anemia (21%-39% of patients)
    • Typically normocytic, normochromic)
    • Rarely acquired hemolytic syndrome from hypophosphatemia accompanying anorexia nervosa (e.g., during the refeeding process)
  • Leukopenia (29%-36% of patients)
    • Mild neutropenia
    • Lymphocytopenia
  • Thrombocytopenia (5-11% of patients)
  • Acanthocytes on peripheral smear
  • Gelatinous transformation or serous atrophy on bone marrow exam

Learn more here.

  • Increase in cardiac output, primarily from increased stroke volume
  • Increase in 2,3-diphosphoglycerate (2,3-DPG), leading to shift of oxygen dissociation curve to the right (lower affinity for oxygen, increased oxygen unloading in tissues)
  • Increase in oxygen extraction by tissues
  • Redistribution of blood flow to vital tissues such as the brain and heart

  • Renal artery stenosis
  • Hydronephrosis
  • Renal cysts
  • Renal tumors

  • Cerebellar hemangioblastoma
  • Hepatocellular carcinoma
  • Uterine leiomyoma
  • Renal cell carcinoma
  • Meningioma
  • Fatigue
  • Pallor
  • Dizziness
  • Headaches
  • Vertigo
  • Tinnitus
  • Dyspnea
  • Inactivity

Teardrop cells are red cells appearing in the shape of a teardrop or a pear with a single, short or long, often blunted or rounded end are called teardrop cells. True tear drops have blunted tips and point in different directions. Teardrop cells are commonly seen in chronic idiopathic myelofibrosis.

Teardrop cell (arrow) from a 68-year-old woman with cirrhosis (100x, oil).

Hemoglobinuria and myoglobinuria

Type I cells – red blood cells (RBCs) express GPI-APs (for example, CD59) at normal density

  • RBCs express normal amounts of GPI-anchored proteins (GPI-AP), such as CD59
  • Full protection against complement-mediated lysis
  • Normal RBC lifespan of about 120 days

Type II cells – red cells partly deficient in GPI-APs;

  • RBCs partly deficient in GPI-APs
  • Partial protection against complement-mediated lysis
  • Lifespan intermediate between type1 and type 3 cells

Type III cells – red cells completely deficient in GPI-APs.

  • RBCs completely deficient in GPI-APs
  • No protection against complement-mediated lysis
  • RBC lifespan 10-15 days

  • Acute intermittent porphyria (AIP)
  • Hereditary coproporphyria (HCP)
  • Variegate porphyria (VP)
  • ALA-dehydratase deficiency porphyria (ADP)
Heme biosynthesis pathway
  • Reduce rates of alloimmunization
  • Reduce rates of febrile nonhemolytic transfusion reactions
  • Prevent cytomegalovirus transmission
Meds, medications; MM, multiple myeloma; MDS, myelodysplastic syndrome; mets, metastases; DIC, disseminated intravascular coagulation.
See graphic.

Another perspective:

  • Mean cell volume (MCV)
  • Mean corpuscular hemoglobin (MCH)
  • Mean corpuscular hemoglobin concentration (MCHC)
  • Red cell distribution width (RDW)
From Pediatr Clin North Am. 2013;60:1349-62.
National Comprehensive Cancer Network (NCCN) and European LeukemiaNet (ELN) recommend WHO 2016 diagnostic criteria (above) for most accurate diagnosis. Hemoglobin thresholds for men and women were lowered in the 2016 revision to the WHO diagnostic criteria (16.5 g/dL for men or 16 g/dL for women) to include most cases of masked PV that were missed by the 2008 WHO criteria (18.5 g/dL for men and 16.5 g/dL for women).

Learn more here.

  • Helmet cells
  • Keratocytes (horn cells)
  • Crescents
  • Triangles
  • Microspherocytes

For more information see. Additional images shown here.

  • Eliminate precipitating factors
  • Treat patient’s symptoms
  • Reduce ALAS-1 activity and production of 5-aminolevulinic acid (ALA) and porphobilinogen (PBG) using:
    • Carbohydrate loading
    • Heme infusions

Thrombosis and disease progression to myelofibrosis or acute leukemia. Learn more here.

  • Homozygous sickle cell disease (HbSS)
  • Sickle beta0 thalassemia
  • Sickle hemoglobin C disease
  • Sickle beta+ thalassemia
From NHLBI 2014 clinical guideline

  • Thrombophlebitis
  • Coagulopathy
  • Hepatic iron overload (with chronic use)

Learn more here.

Learn more here.

Acquired mutation in the X-linked phosphatidylinositol glycan class A (PIGA) gene in an hematopoietic stem cell, leading to deficiency of GPI-anchored proteins on hematopoietic cells, including CD55 and CD59, which in turn leads to activation of the alternative complement pathway and complement-mediated hemolysis. Learn more here.

(A) In healthy subjects, GPI-anchored protein biosynthesis proceeds unperturbed in the endoplasmic reticulum. The full-length GPI anchor with attached protein (e.g., CD55 and CD59) resides in the membrane rafts of blood cells; thus red cells are protected from complement-mediated hemolysis. (B) In PIGA-PNH, a somatic mutation in PIGA  (required for the initial step in GPI-anchored biosynthesis) leads to failure to generate the GPI anchor in hematopoietic cells. After expansion of the PNH clone (often through immunologic escape) the PNH red cells are susceptible to complement-mediated hemolysis due to an absence of the GPI-anchored CD55 and CD59 from the cell surface. From RA Brodsky.

Aggregation of sickled cells, causing vaso-occlusion of small blood vessels, leading, in turn, to ischemia-reperfusion injury.

From Shutterstock, with permission

Learn more here.

  • Conditions involving macrophage-mediated ingestion or red cells:
    • Hemophagocytic lymphohistiocytosis (HLH)
    • Pernicious anemia
    • Resorbing hematoma
  • Conditions not associated with red cell destruction:
    • Cirrhosis may also mimic hemolysis because the liver is responsible for synthesizing haptoglobin and hepatocytes release LDH, and AST may be elevated disproportionately to ALT, especially in alcoholic liver disease.
  • Iron levels
    • Iron increases hepcidin levels.
    • Represents a feedback mechanism to maintain stable body iron levels.
  • Inflammation 
    • Leads to increased hepcidin levels.
    • Represents a host defense mechanism to limit extracellular iron availability to microbes.
  • Erythropoiesis
    • Increased erythroid activity leads to decreased hepcidin levels.
    • Ensures iron supply for erythropoiesis.
    • Erythropoietic drive overrides both iron sensing and inflammation sensing mechanisms to control hepcidin levels.

Autoimmune hemolytic anemia

Acute intermittent porphyria

Genetics in Medicine • Volume 13, Number 2, February 2011

Direct antiglobulin test


Glucose-6-phosphate dehydrogenase. Learn more here.

Microangiopathic hemolytic anemia

Paroxysmal nocturnal hemoglobinuria

Packed red blood cells, used for transfusion.

Polycythemia vera

Red cell distribution width

Sickle cell anemia

Sickle cell disease

  • Hypochromic microcytic red cells
  • Pencil cells, which is a type of elliptocyte, reported in about two-thirds of cases
  • Target cells
  • Fragments (in severe cases)
  • Thrombocytosis (in about 10% of cases)

Transferrin saturation. Represents the % of iron binding sites on serum transferrin that are bound by iron atoms.

Vaso-occlusive crisis, occurs in patients with sickle cell disease (SCD). The most frequent cause of recurrent morbidity and SCD-related admission to hospital.


  • Hemoglobin (Hb)
  • Red blood cell (RBC) count
  • Mean cell volume (MCV)


  • Hematocrit (Hct) = MCV x RBC count
  • Mean corpuscular hemoglobin (MCH) = Hb/RBC count
  • Mean corpuscular hemoglobin concentration (MCHC) = Hb/Hct
  • Hormonal fluctuations during the menstrual cycle
  • Fasting (reduction in calorie intake)
  • Smoking
  • Infections
  • Alcohol
  • Exposure to porphyrinogenic drugs including:
    • Antibiotics
    • Oral contraception
    • Anticonvulsants

Read more here.

In one study:

  • Normal platelet count in 84.6%
  • Thrombocytosis (> 400 × 10 9/L) in 13.3%
  • Thrombocytopenia (< 150 × 10 9/L) in 2.1%

They become smaller, they acquire a larger surface-to-volume ratio, they lose their organelles and the mean corpuscular hemoglobin concentration increases.

On Wright-Giemsa stained peripheral blood, reticulocytes have a purplish hue owing to the presence of residual RNA. These are called polychromatophilic cells (arrow).

British Society for Haematology recommends investigating patients with persistently elevated venous hematocrit (Hct) (> 52% in males and > 48% in females)

FDA test requirements (with American Red Cross guidance):

  • Hepatitis B virus (HBV):
    •  The tests used for blood donor screening are the GS HBsAg EIA 3.0, a qualitative ELISA for the detection of Hepatitis B Surface Antigen (HBsAg), and the Ortho HBc ELISA for the qualitative detection of antibody to HBV core antigen (anti-HBc) in human serum and plasma samples. 
    • An FDA licensed triplex nucleic acid test (NAT) using transcription-mediated amplification was introduced by the Red Cross in 2009. The assay detects HBV DNA, HIV-1 RNA, and HCV RNA. 
    • The frequency of detecting an active HBV infection in a blood donor is about 1 per 12,000 donations screened.
    • The per-unit risk of HBV infection through blood transfusion is less than 1 per million units screened. 
  • Hepatitis C (HCV):
    • The test used for blood donor screening is the Ortho HCV ELISA for the qualitative detection of antibody to HCV antibodies (anti-HCV) in human serum or plasma samples.
    • A duplex nucleic acid test (NAT) was introduced for HIV-1/HCV RNA detection in 1999 and updated to include the detection of HBV DNA in 2009.
    • Donors who test HCV-antibody reactive, but NAT nonreactive by routine testing are further tested individually for HCV RNA by NAT.
    • Donors who test anti-HCV and HCV NAT reactive do not require further testing. 
    • The frequency of detecting a positive donor is about 1 per 5,000 donations screened.
    • The per-unit risk of HCV infection through blood transfusion is less than 1 per 2 million units screened. 
  • HIV:
    • The test used for blood donor screening is the GS HIV-1/HIV-2 PLUS O EIA for the simultaneous qualitative detection of anti-HIV 1 (groups M and O) and/or HIV-2 in human serum or plasma. 
    •  A duplex nucleic acid test (NAT) was introduced for HIV-1/HCV RNA detection in 1999 and updated to include the detection of HBV DNA in 2009.
    • Donors who test antibody reactive are further evaluated by additional tests to confirm the presence of HIV antibody and to differentiate HIV-1 from HIV-2 antibodies. 
    • Donors who test anti-HIV-1/HIV-2 and HIV-1 NAT reactive are not further tested.
    • The frequency of detecting HIV-1 in a blood donor is about 1 per 33,000 donations screened.
    •  detecting HIV-2 in a blood donor is extremely rare at 1 per 57 million donations, with only 5 such infected donors ever identified since HIV-2 screening began in 1992.
    • The per-unit risk of HIV-1 infection through blood transfusion is less than 1 per 2 million units screened. 
  • Human T-cell lymphotropic virus I/II (HTLV-I/II):
    • The test used for blood donor screening is the Avioq HTLV-1/2 Microelisa system for the qualitative detection of antibodies to HTLV-1 and HTLV-2 in human serum or plasma samples.
    • Donors who test reactive for anti-HTLV-1/2 are further tested using an FDA licensed western blot to determine if antibodies are present. 
    • There are no nucleic acid tests (NAT) available for HTLV-1/2.
    • The per-unit risk of transfusion-transmitted HTLV-1/2 is less than 1 per 2 million units screened, and the frequency of detecting an infected donor is 1 per 27,000 donations screened.
  • Syphilis:
    • Screening for syphilis is performed using a qualitative test that detects the presence of antibodies to the spirochete (corkscrew-shaped bacterium), Treponema pallidum, by an automated agglutination assay based on specific pattern recognition. C
    • Confirmation is performed using another serologic test for total antibodies, an enzyme-linked immunoassay, as well as a test for reagin (a protein-like substance that is present during acute infection and for several months following resolution of infection). 
    • No cases of transfusion-transmitted syphilis have been recorded in more than 50 years. 
  • West Nile virus (WNV):
    • WNV RNA is detected by an FDA licensed NAT assay similar to that used for HIV-1, HCV, HBV, and Zika virus. 
    • NAT-reactive donations are further tested by repeat NAT and antibody to confirm infection. 
    • Following the introduction of blood donor screening, there have been 15 cases of transfusion transmission from screened blood; all are believed to be due to donations having very low levels of virus. This translates to a risk of about 1 per 84 million donations for the Red Cross overall (or 1 per 35 million during the summer transmission season). 
  • Trypanosoma cruzi:
    • The Red Cross blood donations are screened using the Ortho T. cruzi Enzyme-Linked Immunosorbent Assay (ELISA) for the qualitative detection of antibodies to T. cruzi in human serum or plasma samples.
    • An FDA licensed enzyme strip immunoassay (ESA) is used for confirmatory testing.
    • Because T. cruzi is not endemic in the United States, the Red Cross (and all US blood centers) donors are tested only once.
    • The frequency of detecting a positive donor is about 1 per 15,000 first-time donations screened.
  • Babesiosis:
    •  In May 2018, the Red Cross began testing from whole blood samples using a NAT assay that detects the main four species of babesia pathogenic to humans. The assay, now FDA licensed, detects ribosomal RNA of the parasite following red cell lysis, significantly increasing sensitivity and obviating the need for antibody testing.
    • Tested in 14 states in the US where incidence of infection is highest.

Refers to changes in quality and quantity of packed red blood cells (pRBCs) during storage, including:

  • Change in cell shape change and microvesiculation
  • Decrease in adenosine triphosphate (ATP) and 2,3-diphosphoglycerate levels
  • Increase in lysophospholipids
  • Increase in potassium
  • Increase in free hemoglobin (Hb)

The storage lesion represents a risk to efficient RBC perfusion and tissue oxygen delivery, and it has been suggested that it may result in adverse outcomes. This has led to the classification of “young” (21 days) RBC units. According to the AABB, 13 randomized control trials have evaluated the effect of RBC storage duration of transfused RBCs on patient outcomes (7 since 2012). However, there is currently no formal guidance on the optimal length of RBC storage prior to transfusion. The AABB recommends administering RBC units within licensed expiration date (standard issue) rather than transfusing only fresh RBCs (< 10 days old) to patients, including neonates.

Burr cells are red blood cells (RBCs) with 10-30 uniform, short, blunt projections distributed evenly around the circumference of the cell, giving the red cell surface a serrated appearance. The red blood cells retain central pallor. They are found in uremia, and to a lesser extent post splenectomy. Cells resembling burr cells (called crenated RBCs) occur when blood is stored too long in EDTA-containing tubes.

Echinocyte - Wikipedia
Scanning electron microscopy (SEM) of echinocytes (from Wikipedia)
Wright stained peripheral blood smear from a patient with end-stage kidney disease showing multiple burr cells.

A cold reactive antibody that causes agglutination without antiglobulin antisera at 4 degrees C (39.2 degrees F).

The first automated counters to hit the market was the Coulter counter, named after its inventor, Wallace H. Coulter, an electrical engineer. These early counters used what is now known as the Coulter principle, which states that particles (for example a red blood cell) that pass through an orifice with an electric current, produce a change in impedance that is proportional to the volume of the particle. That change is registered and recorded. Coulter patented his method in 1953.

Serological or electronic crossmatches are performed to detect serological incompatibility (the presence of antibodies) between recipient and donor before transfusion.

AHG, anti-human globulin.

According to the AABB:

Defined as ≥ 1 degrees C increase in temperature ≥ 38 degrees C (100.4 degrees F) that is associated with transfusion and no other causes are evident. Caused by antibody to donor leukocytes. Symptoms include:

  • Fever
  • Chills
  • Tachypnea
  • Headache
  • Vomiting

According to the AABB, febrile nonhemolytic transfusion reaction defined as fever and/or chills without hemolysis occurring
in the patient during or within 4 hours of cessation of transfusion. If transfusion-related, the most common cause is a reaction to passively transfused cytokines or a reaction of recipient antibodies and leukocytes in the blood product. If blood culture of patient or residual component is performed, the results should be negative. Laboratory findings should show no evidence of
acute hemolysis.

Treatment includes antipyretic such as acetaminophen or meperidine (for more severe reactions).

Administer leukocyte-reduced blood or washed RBCs to reduce risk.

Howell-Jolly bodies are nuclear remnants in red blood cells, typically about 1 μm in diameter. As such, they are composed of DNA. Their presence indicates asplenia. Learn more about the history of discovery of the Howell-Jolly body here.

41% – 50% in male adults and 36% to 44% in female adults.

4.5-5.9 × 1012/L for male persons and 4.0-5.2 × 1012/L in female persons.

Note: 1012 = trillion!

On average about 1/3 of iron binding sites are occupied with iron atoms. Normal values, however, can range between 20-45%.

An abnormally shaped red cell

Examples of poikilocytes include:

  • Sickle cells (drepanocytes)
  • Burr cells (echinocytes)
  • Spur cells (acanthocytes)
  • Target cells (codocytes)
  • Spherocytes
  • Elliptocytes (includes pencil cells)
  • Stomatocytes
  • Bite cells
  • Tear drop cells (dacrocytes)
  • Schistocytes (includes helmet cells, horn cells, triangular cells, microspherocytes)
  • Fish-shaped red cells

In patients with intense erythropoietic stimulation, “young” basophilic reticulocytes are released prematurely from the bone marrow into the peripheral blood, causing shortened reticulocyte maturation time in the bone marrow (sometimes to < 1 day), but a longer reticulocyte maturation time in the peripheral blood. The RPI is a corrected reticulocyte count that accounts for reticulocytes in all development stages.

Reticulocyte production (maturation) index = reticulocyte count [%] × patient’s packed cell volume/0.45) / maturation time in peripheral blood.

Maturation time (days) varies according to Hct:

Hematocrit (%)Maturation correction
< 152.5

Reticulocyte production index of > 3 suggests normal bone marrow response to anemia while < 2 suggests inadequate response.

See calculator.

Immature, nonnucleated red blood cell (RBC) that circulates in the blood before losing its RNA and differentiating into mature RBC (the maturation process in the circulation takes 1-3 days). Reticulocytes are larger than mature RBCs, and contain intracellular organelles (with the exception of a nucleus).

Schistocytes, or schizocytes (from the Greek word schisto, broken or cleft) are circulating fragments of red blood cells or red blood cells from which cytoplasmic fragments have been lost. They lack central pallor and are often deeply staining. For more information see. Additional images shown here.

IV transfusion without removing patient blood volume.

A target cell is a red cell with centrally located disk of hemoglobin surrounded by an area of pallor with an outer rim of hemoglobin adjacent to the cell membrane giving the cell the appearance of a bull’s eye or shooting target. Seen in liver disease (macrocytic targets), iron deficiency anemia, and thalassemia (microcytic target cells). Target cells may also be seen in hemoglobin C and E disease, and following splenectomy.

Peripheral smear showing multiple target cells (100x, oil)

Testing for presence of A and B antigens on red blood cells:

  • Forward typing – red blood cells (RBCs) are tested for A and B antigens.
  • Reverse typing – serum or plasma is screened for presence of anti-A and anti-B antibodies.

According to a Circular prepared jointly by AABB, the American Red Cross, America’s Blood Centers, and the Armed Services Blood Program:

The ABO group of all red-cell-containing components must be compatible with ABO antibodies in the recipient’s plasma. Serologic compatibility between recipient and donor must be established before any red-cell containing component is transfused. This may be accomplished by performing ABO/Rh typing, antibody screening, and crossmatching by serologic technique or use of a computer crossmatch.

Interpretation of typing studies and prevalence of blood types. From the AABB.

Red cell mass > 25% above that predicted for sex and body mass.

Acquired alpha-thalassemia most commonly develops in patients with myelodysplastic syndrome. It is caused by inactivating somatic mutations of the trans-acting chromatin-associated factor ATRX, which cause dramatic downregulation of alpha-globin gene expression.

Learn more here.

Occurs when there is a reduction in the synthesis of the α-globin chains of adult hemoglobin (HbA, α2β2) relative to beta-globin synthesis. Underproduction of α globin chains gives rise to excess β-like globin chains which form γ4 tetramers, called Hb Bart’s (in fetal life) and β4 tetramers, called HbH (in adult life).

  • α thalassemia trait:
    • Mutations affecting the α globin genes on one chromosome
    • Associated with minimal anaemia
  • Compound heterozygotes and some homozygotes for α thalassemia (HbH disease):
    • Moderately severe anemia
    • Presence of HbH in the peripheral blood
  • Hb Bart’s hydrops fetalis syndrome:
    • Little or no α globin chains have a very severe form of anaemia
    • May cause death in the neonatal period if left untreated
Genetics in Medicine • Volume 13, Number 2, February 2011

Learn more here.

Acanthocytes are densely stained, spheroidal red blood cells that lack central pallor and have 3-20 irregularly distributed, thorn-like projections of variable size/length/thickness, often with drumstick (knobby) ends. Spicules may occasionally have branches. Typically seen in cirrhosis, but also in hereditary abetalipoproteinemia and related neurological syndromes. Small numbers may be observed post-splenectomy.

Peripheral smear showing acanthocyte in middle of field
3D graphic of acanthocytes in blood (Shutterstock with permission)

Acute, severe reaction, typically caused by red blood cell ABO incompatibility.

According to the AABB, acute hemolytic transfusion reaction is defined as the rapid destruction of red blood cells during,
immediately after, or within 24 hours of cessation of transfusion. Clinical and laboratory signs of hemolysis are present.

Criteria for diagnosis:

According to the AABB, an allergic reaction is the the result of an interaction of an allergen with preformed antibodies. In some instances, infusion of antibodies from an atopic donor may also be involved. It may present with only muccocutaneous signs and symptoms.

Criteria for diagnosis:

Abrupt reduction in hemoglobin in a patient with sickle cell disease, typically caused by parvovirus B19-mediated suppression of red blood cell production.

ABO compatibility verified using computer system without immediate spin or and antiglobulin crossmatching if significant alloantibodies have not been detected in the recipient sample.

Using AABB guidelines, the electronic crossmatch is possible only if the following conditions are met:

  • The patient’s ABO group and Rh type has been done twice and entered in the computer (one group can consist of a record but one must be done on a current in-date specimen). * The computer must alert the technologist if there is a discrepancy between the two groups.
  • The donor ABO (and Rh types, if negative) have been confirmed and entered in the computer. The donor’s unit identification number, component name, and ABO/Rh type must also be entered in the computer (manually or by scanning the bar code label on the unit).
  • The computer system will alert the technologist to ABO & Rh discrepancies between information on the donor label and results of donor confirmatory testing.
  • The computer system will alert the technologist to ensure correct data entry and interpretation, e.g., prevent group O test results from being misinterpreted as group A.
  • The computer system will alert the technologist to ABO and Rh discrepancies patient and donor groups. The program should be programed to prevent assigning ABO incompatible blood (e.g., group A red cells to a group O recipient) and to give an alert when assigning Rh-positive red cells to Rh-negative recipients.

Mild-moderate decrease in serum hemoglobin (Hb rarely < 8 g/dL [80 g/L]), associated with acute or chronic inflammation, in which inflammatory mediators lead to increased hepcidin expression, iron sequestration and reduced erythropoiesis. Learn more here.

Defined as increased heterogeneity (or variation) in red blood cell (RBC) size, which can be measured as cell diameter (on a peripheral smear) or cell volume (using the red cell distribution width [RDW] generated by an automated counter).




Spur cell

Burr cell

Chronic autoimmune atrophic gastritis


Anemia of inflammation

A rare, life-threatening disorder characterized by hypocellular bone marrow resulting in progressive pancytopenia (low reticulocyte, granulocyte, and platelet count) without bone marrow infiltrate, dysplasia or fibrosis. See more here.

A debilitating dermal condition characterized by intense itching, stinging, tingling or burning sensations, without observable
skin lesions, precipitated by contact with water at any temperature. Typically occurs after a shower with warm water. Reported in 5%-69% of patients with polycythemia vera (PV) (41.2% of patients in a recent study of 102 patients with PV). Notably, the onset of aquagenic pruritus precedes diagnosis of PV in almost half of cases.

Congenital secondary erythrocytosis caused by mutations in oxygen sensing/hypoxia-inducible factor (HIF) signaling pathway (autosomal recessive mutations in VHL gene, a negative regulator of hypoxia sensing).

  • First hereditary condition of augmented hypoxia sensing to be recognized.
  • Autosomal recessive disorder with increased serum erythropoietin levels and hemoglobin concentrations in normoxia.
  • Hundreds of patients with Chuvash polycythemia are found in the Chuvash population of central Russia.
  • Mutation for Chuvash polycythemia is 598C>T in the von Hippel-Lindau gene (VHL) on chromosome 3p25.

Read more here.

Acquired uncompensated agglutination and premature destruction of red blood cells (RBCs) by autoantibodies (typically IgM) that target RBC antigens with optimal activity between 0 and 4 degrees C (32-39.2 degrees F), but also react at temperatures > 30 degrees C (86 degrees F). Learn more here.

2014 British Committee for Standards in Haematology (BCSH) guideline suggests using serum cobalamin (vitamin B12) cutoff < 148 pmol/L (200 pg/mL) or cutoff derived from local reference range in patient with strong clinical suspicion for vitamin B12 deficiency:

Vitamin B12 concentrations <200 pg/ml in patients with clinical manifestations have a sensitivity of 90%–95% and an estimated specificity of less than 80%. Learn more here.

Rare Diseases NIH: Autosomal dominant (rarely X-linked) inherited blood disorder that leads to anemia and is associated with physical abnormalities such as small head size (microcephaly) characteristic  facial features, cleft palate, cleft lip, short and webbed neck, small shoulder blades, and defects of the hands (mostly of the thumbs), as well as defects of the genitalia, urinary tract, eyes and heart. Caused by mutations in several genes. Learn more here.

A sickle cell. Some authors used to refer to sickle cell disease as drepanocytosis (for example, see this 1944 paper).

The EMA binding test uses flow cytometry to determine the amount of fluorescence (reflecting EMA bound to specific transmembrane proteins) derived from individual red cells. Red blood cells (RBCs) are incubated with EMA dye, which covalently binds to band 3 and other proteins on RBC surface. The mean fluorescence of EMA-stained RBCs in patients with hereditary spherocytosis is lower when compared with control RBCs due to the decreased amount of target proteins. The EMA binding test is easy to use, and test results are available for reporting in 2–3 h.

Read more here.

An increase in the number of red blood cells (RBCs) relative to the plasma volume. It is manifested by a persistent increase in the venous hematocrit:

  • Relative erythrocytosis – elevated hematocrit associated with normal red cell mass, resulting from contracted plasma volume most often due to dehydration.
  • Absolute erythrocytosis:
    • An increased red cell mass above 125% of the predicted value for the body mass of the patient.
    • Red cell mass is rarely measured; hemoglobin and/or hematocrit typically used as surrogates for red cell mass.

A vasomotor disturbance characterized by periodic attacks with triad of increased temperature, erythema, and burning pain resulting from hyperperfusion of skin areas, especially in the feet and hand. Typically relieved by cooling and aggravated by warming. May be primary or secondary. Causes of secondary erythromelalgia include polycythemia vera and essential thrombocythemia.

Learn more here.

A glycoprotein hormone secreted by peritubular cells in the kidney upon detection of reduced oxygen in the circulation. Binds to the erythropoietin receptor present on erythroid precursor cells in the bone marrow, resulting in stimulation of red blood cell production.

RBC, red blood cell; Epo, erythropoietin

Combined immune thrombocytopenia (ITP) and autoimmune hemolytic anemia. Learn more here.

Acute hemolytic anemia resulting from ingestion of fava beans. Learn more here.

Eculizumab or ravulizumab (C5 inhibitors). Learn more here.

Fluorescent aerolysin, used in flow cytometry to diagnose paroxysmal nocturnal hemoglobinuria (PNH) (selectively binds the GPI anchor with high affinity).

Flow cytometric analysis of granulocytes using FLAER. (A) As a control setting, there was no evidence of decreased (type II PNH cells) or absent (type III PNH cells) expression of FLAER. (B) In this patient, decreased (42.4%) and absent (57.0%) FLAER fractions were detected, suggesting that 99.4% of PNH granulocyte clones had a FLAER deficiency, which is consistent with classic PNH. Source.

A condition in which body iron stores are normal or increased, but iron incorporation into red cell precursors is impaired. One example is anemia of inflammation.

An X-linked genetic disorder caused by mutations in G6PD gene resulting in reduced activity of the G6PD enzyme. Learn more here.

Cureus | Prevalence of Glucose-6-Phosphate Dehydrogenase Deficiency Among  Children in Eastern Saudi Arabia

HbH is comprised of β4 tetramers made from excess β globin chains in alpha thalassemia.

Learn more here.

A 25-amino acid peptide hormone produced by liver hepatocytes in response to circulating iron levels which inhibits iron absorption from the intestinal mucosal cells and release by macrophages and hepatocytes through degradation of ferroportin-1. Hepcidin plays a critical role in iron absorption and recycling. Learn more here.

Hydroxyurea is a ribonucleotide reductase inhibitor

Ribonucleotide reductase, one of the most essential enzymes of life, and how it buries the RNA world Fcimb_04_00052_pdf_Page_1
From the following link.

Refers to the inability to produce adequate number of red blood cells in the presence of increased immature erythroid precursors.

Per Cazzola, M.:

  • In ineffective erythropoiesis, the erythroid marrow is active and expanded (erythroid hyperplasia) but its efficacy in terms of red cell production is impaired and may lead to anemia.
  • Erythroblasts are predominant in the bone marrow, and the M/E ratio is <1:1.
  • Ineffective erythropoiesis is a major pathogenetic mechanism that is responsible for anemia in several inherited and acquired disorders, including:
    • Thalassemia:
      • Transfusion-dependent β-thalassemia (also known as β-thalassemia major) 
      • Nontransfusion-dependent β-thalassemia (also known as β-thalassemia intermedia; including β-thalassemia/Hb E) 
    • Inherited sideroblastic anemias 
    • Congenital dyserythropoietic anemias
    • Megaloblastic anemias 
    • Myelodysplastic syndrome 
  • Patients with ineffective erythropoiesis may have evidence of parenchymal iron overload, which derives from suppression of hepcidin production.

Lactate dehydrogenase (LDH) is a ubiquitous enzyme that catalyzes the conversion of lactate to pyruvate and back, resulting in conversion of NAD⁺ to NADH and back. LDH exists in five distinct forms, named LDH-1 through LDH-5, each having differential expression in different tissues:

  • LDH-1 is found primarily in heart muscle.
  • LDH-2 is the major isozyme of the reticuloendothelial system and red blood cells.
  • LDH-3 is highest in the lung.
  • LDH-4 is highest in the kidney, placenta, and pancreas.
  • LDH-5 is highest in the liver and skeletal muscle.
The red cell is a “fermenter“. It generates all of its energy from glycolysis without use of the Krebs cycle, yielding 2 molecules of ATP for very molecule of glucose. Instead of entering the Krebs cycle in the mitochondria (red cells do not have any mitochondria), pyruvate is metabolized to lactate via LDH.

Meets the criteria for diagnosis polycythemia vera despite lower-than-threshold hemoglobin/Hct.

Hemolytic anemia + schistocytes on the peripheral smear caused by high shear environment from partially occluded vessels or paravalvular jet streams (in the latter case, the term MAHA is used even though a paravalvular leak does not involve the microvasculature).

Free, unbound iron in the plasma. Consists of multiple chemical structures of iron (including labile plasma iron) associated with other plasma components. Typically appear when transferrin saturation > 70%. Rapidly taken up by parenchymal cells of the liver, heart, anterior pituitary cells and pancreas, where they generate reactive oxygen species and cause organ damage.

Learn more here.

Monitors the extent of red blood cell (RBC) shape change (elongation index) within a range of osmotic gradient under known shear stress and is a measure of hydration status of RBCs. Used to diagnose RBC membrane disorders.

The osmoscan module of LoRRca MaxSis is performed by adding 250 uL of whole blood to 5 mL of iso-osmolar polyvinylpyrrolidone (isoPVP). The diluted RBC suspension is submitted to an increasing osmotic gradient (from 80 mOsmol/L to 500 mOsmol/L) under a constant shear stress of 30 mPa. From Llaudet-Planas et al.

Read more here.

A form of pica, defined by eating of at least a tray of ice daily for 2 months or of ice chips. Accounts for over 50% of pica in patients with iron deficiency. Learn more here.

A chronic myeloproliferative neoplasm associated with increased risk of thrombosis and bleeding, and disease progression to either myelofibrosis and/or acute leukemia. Caused by somatic mutations in JAK2 (Janus kinase), typically V617F.

Porphyrias are a group of eight panethnic inherited metabolic disorders of heme biosynthesis. Each results
from a specific enzymatic alteration in the heme biosynthesis pathway.

Learn more here.

Hematocrit > 51% lasting > 1 month post transplantation (usually develops within the first year post transplant). Occurs in 10%-15% of renal transplant recipients and is usually self-limiting. Most common after kidney transplant, but may also occur after other types of transplant, including hematopoietic stem cell transplantation. Learn more here.

A type of absolute erythrocytosis (increased red cell mass) caused by an intrinsic defect in the stem cell population leading to
autonomous proliferation of red cell progenitors within the bone marrow. There are two types of primary erythrocytosis:

  • Congenital erythrocytosis (primary familial or congenital polycythemia) caused by gain of function mutations in the erythropoietin receptor.
  • Acquired erythrocytosis (polycythemia vera) caused by a somatic mutation in the Jak2 gene.

A syndrome characterized by isolated normocytic normochromic anemia with severe reticulocytopenia and significant reduction or absence of erythroid precursors in bone marrow. Learn more here.

A trace byproduct of the last step in heme synthesis. In iron deficiency, zinc, instead of iron, is incorporated into the protoporphyrin ring, resulting in increased zinc protoporphyrin levels (iron protoporphyrin is also called heme). ZPP may be used as an assay for iron deficiency.

Heme synthesis from succinyl-CoA to PPIX and ultimately heme. Synthesis of ALA is the rate-limiting step and under negative feedback control of heme (green/ dashed). A deficiency of iron supply limits heme synthesis and leads to PPIX accumulation. Zinc can then substitute for iron and ferrochelatase catalyzes the formation of zinc PPIX (red/dotted). From the following link.

Elevated hematocrit associated with normal red cell mass resulting from contracted plasma volume most often due to dehydration.

  • Absence or presence of PNH clone
  • Clone size in red blood cells:
    • Total PNH clone size
    • Percentages of Type II and type III cells
  • PNH clone size in white blood cells:
    • Neutrophils
    • Monocytes

Learn more here.

Sleep-related sensorimotor disorder characterized by an urge to move that occurs during rest or is exacerbated by rest, occurs in the evening or night and disappears or improves with movement. The pathophysiology is unknown.

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Rouleaux is the arrangement of >3 red cells in a linear of branched pattern resembling a stack of counts. Seen in conditions associated with an inflammatory response and acute phase reaction or multiple myeloma.

Elevated red cell mass (absolute erythrocytosis) caused by a factor external from the bone marrow, typically erythropoietin (other factors include testosterone and cortisol). Learn more here.

A very small fraction of total ferritin circulates in blood. In contrast to its cellular counterpart, serum ferritin does not contain any iron and is almost entirely made up of L chains. It does not play a role in iron transport or cellular iron uptake. Indeed, its function is unknown. Serum ferritin is widely used as a convenient surrogate measure of body iron stores.

A group of chronic hemolytic anemias characterized by the presence of at least one hemoglobin S allele (HbS; p.Glu6Val in HBB) and a second HBB pathogenic variant leading to excessive production of hemoglobin S (HbS). Learn more here.

Hemolytic uremic syndrome caused by Shiga toxin-producing Escherichia coli (STEC).

Learn more here.

Screening for complement-activating alloantibodies in a patient who will receive a blood transfusion, using commercially available group O RBCs that express all antigens as required by the FDA.

Per the AABB:

Pretransfusion compatibility testing begins with the type and screen procedure. The recipient’s ABO group and Rh type are determined first; then a screening procedure is used to detect any unexpected non-ABO blood group antibodies that may be present. If the screening test reveals the presence of an antibody, the specificity of that antibody is determined by an antibody identification panel. Once the specificity of the antibody has been identified, donor units of the appropriate ABO group and Rh type are screened for the corresponding antigen. Units that are negative for that antigen are crossmatched with the recipient to ensure compatibility.

Antibody screening using an indirect antiglobulin test. Commercially available group O RBCs for antibody screening may be performed by 2 reagent single donor RBCs or 3 reagent single-donor RBCs. if antibody screen is positive, serum or plasma samples are tested against a panel of group O RBCs (typically 8-14 samples) with known antigenic composition to identify alloantibody specificity.

7.5 microns

Morphological Abnormalities of Red Blood Cells – The Art Of Medicine

Caused by inactivating somatic mutations of the trans-acting chromatin-associated factor ATRX, which cause dramatic downregulation of alpha-globin gene expression.

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Partial deficiency of the third enzyme of heme synthesis, porphobilinogen deaminase (or hydroxymethylbilane synthase). AIP is an autosomal dominant condition.

Heme biosynthesis pathway showing location of enzymatic defect in AIP.

Autosomal dominant mutations of one of the following genes:

  • SPTA1 encoding alpha-spectrin
  • SPTB encoding beta-spectrin
  • EPB41 encoding protein 4.1

Autosomal recessive mutations in one of the following genes:

  • SPTA1 (encoding alpha-spectrin)
  • SPTB (encoding beta-spectrin)
  • EPB41 (encoding protein 4.1)
British Committee Standards in Haematology (BCSH) expert guideline on diagnosis of hereditary spherocytosis can be found in Br J Haematol 2012 Jan;156(1):37

Autosomal dominant (75% of cases) or autosomal recessive (25%) mutations in genes that encode red blood cell (RBC) membrane proteins, resulting in qualitative defects of the encoded proteins. Genes with mutations include:

  • ANK1 encoding ankyrin
  • SLC4A1 encoding band 3
  • SPTA1 encoding alpha-spectrin
  • SPTB encoding beta-spectrin
  • EPB42 encoding protein 4.2

Mutations results in reduced binding of spectrin cytoskeleton to lipid bilayer of RBCs, leading to reduced membrane surface area (reduced surface area-to-volume ratio), reduced RBC deformability and increased osmotic fragility.

Autoimmune-mediated atrophic gastritis resulting from the destruction of gastric parietal cells and leading to deficient production of intrinsic factor (necessary for vitamin B12 absorption), and reduced vitamin B12 absorption. The immune response is directed against the gastric H/K–ATPase, which accounts for associated achlorhydria.

See more here.

Somatic mutations in JAK2 (Janus kinase), specifically V617F in exon 14 (reported in about 95% of patients) and mutations in exon 12 (reported in about 4% of patients), leading to constitutive activation of Jak2 signaling in hematopoietic stem cells.

Congenital gain-of-function mutations in erythropoietin receptor (EPOR)

Autoantibody, typically IgG, directed against red blood cell self-antigens with maximal reactivity at 37 degrees C (98.6 degrees F). Learn more here.

  • Thrombocytopenia,
  • Microangiopathic hemolytic anaemia
  • Damage to various organs, predominantly the kidney and the brain

Learn more here.

About 10%

  • Hemolytic anemia
  • Bone marrow failure
  • Thrombosis

The common feature to all forms of hemolytic uremic syndrome is the presence of endothelial cell lesions in the microvasculature of the kidney and, less frequently, of other organs… all forms of hemolytic uremic syndrome share a final common procoagulant and proinflammatory phenotype of activated endothelial cells.

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Receptor in the terminal ileum that binds and internalizes the vitamin B12-intrinsic factor complex. Learn more here.

Based on spectrophotometric measurement of cyanide derivative of hemoglobin.

Protocol includes:

  • Blood is mixed with a solution containing potassium cyanide and potassium ferricyanide (Drabkin’s solution).
  • The red blood cells are lysed, producing an evenly disturbed hemoglobin solution.
  • Potassium ferricyanide transforms hemoglobin into methemoglobin, and methemoglobin combines with potassium cyanide to produce hemiglobincyanide (cyanmethemoglobin).
  • Cyanmethemoglobin has a peak absorbance at 540 nm and is measured photometrically.
  • The absorbance is compared with that of the standard hemiglobincyanide solution by using a formula to obtain the amount of hemoglobin.

Hb<13 g/dL in men, Hb < 12 g/dL in women (<11 g/dL if pregnant)

Although the terms are often used interchangeably, they have slightly different meanings.

Erythrocytosis is an increase in red blood cells (RBCs) relative to the volume of blood. Primary erythrocytosis is associated with an elevated red cell mass (a change in the numerator in RBC/volume), while relative erythrocytosis is not (rather, it is a change in the denominator in RBC/volume). An important caveat is that an increased number of microcytic RBCs, for example in thalassemia, may be associated with a normal or even low red cell mass (Hct=MVC x RBC count). Indeed, before its cause was known thalassemia was historically referred to as microcytic erythrocytosis.

Polycythemia refers to increased red cell mass, manifested by increased Hct and/or hemoglobin, and usually caused by increased RBC count (erythrocytosis). In theory, an elevated MCV could produce increased red cell mass independent of RBC number (Hct=MVC x RBC count). As the name ‘poly’ implies, polycythemia more accurately refers to pan-myeloproliferation, but this definition is not normally adhered to.

Hb measures the total weight of hemoglobin contained within a given volume of blood. It is reported in g/dl or g/L. The Hct is the fractional volume of blood that is comprised of red cell cells. The Hct is expressed as a percentage.

A polychromatophilic cell is a red cell that is slightly larger than a mature red cell whose cytoplasm has a bluish tinge when observed on a normally stained peripheral smear. Most if not all of these cells correspond to reticulocytes, which are RNA containing red cells that are detected either with intravital stains (where blood is not fixed, but rather incubated alive with stain) or FACS analysis using an RNA fluorochrome. Reticulocyte staining is more sensitive than Wright-Giemsa staining for detecting reticulocytes: all true polychromatic cells are reticulocytes, whereas not all reticulocytes would be detectable as polychromatic cells.

Peripheral smear (Wright stained) showing polychromatophilic cell (arrow) (100X, oil)
Intravital stain of peripheral blood showing several reticulocytes, notable for their slightly larger size than mature red cells and presence of reticulin network within the cytoplasm. From Shutterstock with permission

Sickle cell anemia is a subset of sickle disease that includes the 2 most severe forms: homozygous sickle cell disease (HbSS), sickle beta0 thalassemia.

CAD, cold agglutinin disease; MDS, myelodysplastic syndrome; AA, aplastic anemia; MGUS, monoclonal gammopathy of unknown significance; MM, multiple myeloma; RBC, red blood cell; MCV, mean cell volume.

1000 μg vitamin B12 daily. Learn more here.

 1-4 mg/kg/day IV for 3-14 days based on clinical signs; do not exceed 6 mg/kg/day. Learn more here.

Erythrocyte sedimentation rate is the distance red cells fall by gravity in a vertical tube of anticoagulated whole blood. Learn more here.

From Shutterstock, with permission.

Each unit of RBCs contains enough hemoglobin to increase the hemoglobin concentration in an average-sized adult by approximately 1 gram/deciliter (g/dL) (increase hematocrit by 3%). Learn more here.

Examination of urine for excess porphobilinogen (measurement of 5-aminolaevulinic acid is not essential to establish the diagnosis). Elevated porphobilinogen levels in urine (or plasma) are specific for acute porphyria. The test can be performed in a random sample with the result normalized per gram of urine creatinine; a 24-hour collection is not required.

Urinary porphobilinogen and 5-aminolaevulinic acid are increased in all three acute hepatic porphyrias (acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria) although the concentrations are higher and longer lasting in acute intermittent porphyria than in the other two types (hereditary coporphyria and variegate porphyria).

With a recorded porphobilinogen over excretion (>10 times the upper limit), treatment can be started immediately, with further laboratory investigations used to define the porphyria type in the proband.

For diagnosis of the type of acute porphyria in the proband, plasma fluorescence emission spectroscopy is a fi rst-line test because a peak at 624–628 nm establishes the diagnosis of variegate porphyria.

Learn more here.

Involved in the biosynthesis of glycosylphosphatidylinositol (GPI) anchors, including CD55 and CD59.

Global anemia prevalence in 2010 was 32.9%, causing 68.36 (95% uncertainty interval [UI], 40.98 to 107.54) million years lived with disability (8.8% of total for all conditions [95% UI, 6.3% to 11.7%]). In 2013 nearly 2 billion people or 27% of the world’s population were affected.

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Typically to maintain HbS level at < 30% immediately prior to next transfusion.

Fraction of whole blood that is made of RBCs (also known as packed cell volume).

Tube containing anticoagulated blood spun in a centrifuge. RBC, red blood cell.

Inheritance of AIP, VP and HCP is autosomal dominant.

Jak2 V617F mutation is a G to T somatic mutation at nucleotide 1,849 in exon 14 of JAK2, leading to constitutive activation of signaling pathways downstream of the erythropoietin receptor. It occurs in 95% of patients with polycythemia vera as well as a smaller percentage of patients with other myeloproliferative neoplasms, encodes a constitutively active Janus kinase that upregulates JAK/STAT signal transduction, resulting in unregulated myeloproliferation (erythrocytosis, often with leukocytosis and/or thrombocytosis).

May occur in:

  • Polycythemia vera (95% of cases)
  • Essential thrombocythemia (50-60% of cases)
  • Primary myelofibrosis (50-60% of cases)
  • Refractory anemia with ringed sideroblasts associated with significant thrombocytosis (50% of cases)
EPOR, erythropoietin receptor; FERM = N-terminal Band 4.1, ezrin, radixin, moesin domain; JH1 and JH2 = Jak homology 1 and 2 domains; SH2 = Src homology 2 domain.

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Meningococcal meningitis, which occurred in two of 100 patients included in prospective trials. Patients receiving eculizumab should receive specific meningococcal prophylaxis.

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Represents mean weight of hemoglobin (Hb) per red blood cell (RBC); calculated by dividing hemoglobin (Hb) by the RBC count (RBC).


Imagine drilling a hole in a single red blood cell and weighing the hemoglobin inside. Carry out this procedure on millions of cells, and calculate the average weight. That value is the mean cell hemoglobin!

Measures concentration of hemoglobin (Hb) per unit volume of red blood cells (RBCs); calculated by dividing hemoglobin (Hb) by hematocrit (Hct).

MCHC = Hb/Hct

Under normal conditions:
330 g/L = 150 g/L/0.45

The central white color represents the central pallor observed in RBCs on a Wright-Giemsa stained peripheral smear.

Defined as the value that describes the average size of red blood cells in a blood sample. Individual red blood cells may be microcytic, normocytic or macrocytic.

Normal MCV is 80-100 fL.

120 days

Crizanlizumab is a monoclonal antibody medication that binds to P-selectin, inhibiting white blood cell-endothelial and platelet-endothelial interactions on the blood vessel wall.

Overproduction of neurotoxic heme precursor from the liver caused by deficient enzyme in heme biosynthesis pathway, often in conjunction with precipitating factor that increases rate of heme synthesis. Learn more here.

Jak2 mutation (V617F)

Iron deficiency anemia, reported to account for about 50% of cases.

Vaso-occlusive crisis Learn more here.

Menstrual blood loss.

Blood loss from the gastrointestinal tract.

Hereditary spherocytosis; reported prevalence from 1 in 1,000 to 1 in 3,000 persons.

Babesia microti

At steady state, about 1%-2% of circulating red blood cells (RBCs) are reticulocytes, corresponding to an absolute reticulocyte count of approximately 25-100 × 109/L.

32-36 g/dL

80-100 fL

Measures red blood cell (RBC) lysis incubated in solution of varying concentrations of sodium chloride. RBC lysis is measured by detection of light absorbance by free hemoglobin immediately after sampling and after 24-hour incubation at 37 degrees C (98.6 degrees F). Osmotically fragile cells, such as spherocytes, lyse at relatively lower saline concentrations compared to normal RBCs.

Hypoxia-inducible factor 1-alpha (HIF1-alpha)

Measures proportion of RBCs that have a cellular hemoglobin weight of < 17 pg (analogous to the mean corpuscular hemoglobin, not mean corpuscular concentration - in other words, the term hypochromic is misleading). The parameter is available in some automated hematology analyzers. May be helpful for the assessment of iron availability (absolute or functional deficiency) for erythropoiesis.

A rare disorder associated with triad of:

  • Postcricoid dysphagia which is:
    • Typically painless, intermittent or progressive over years, and limited to solids
    • Occasionally associated with weight loss
  • Iron deficiency anemia
  • Upper esophageal webs

Other features:

  • Most of the patients are white middle-aged women, in the fourth to seventh decade of life.
  • The dysphagia is usually painless and intermittent or progressive over years, limited to solids and sometimes associated with weight loss.
  • Reported to be a risk factor for developing squamous cell carcinoma of the upper gastrointestinal tract.

Learn more here.

Anemia of inflammation (the anemia is not always chronic in nature).


Estimated to affect about one in 75,000 people in European countries, apart from in northern Sweden, where, because of a founder effect, it is more frequent (one in 1000).

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5.4% in the United States, up to 80% in resource-limited countries. Learn more here.

Reported prevalence of anemia from all causes 33%-49% in patients with bariatric procedures. Learn more here.

  • Mild anemia (Hb 9.5–10.9 g/dl) – 30%
  • Moderate anemia (Hb 8.0 and 9.4 g/dl) – 9%
  • Severe anemia (Hb 6.5–7.9 g/dl) – 1%

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12%-24% reported prevalence of anemia from all causes in patients with IBD. Learn more here.

About 17%.

Figure 1. Increase in prevalence of late-life anemia. Increase in prevalence of anemia as defined by WHO (Hb ,12 g/dL in women and ,13 g/dL in men) with advanced age; cohort of 19,758 university hospital inpatients and outpatients. Source.

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0·23–0·42 cases per million population. Learn more here.

Iron deficiency reported to occur in > 30% of patients after 5 years from surgery, with similar rate after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy. Learn more here.

Reported prevalence of iron deficiency in pregnancy 18%:

  • 7% in the first trimester
  • 30% in the third trimester

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Reported prevalence of iron deficiency approximately 1% in male adults and ≥ 11% in female adults. Learn more here.

Macrocytosis occurs in about 3% of the general population.

The variability in year of publication, statistical rigor, the mean cell volume (MCV) cutoff used to define macrocytosis and the different patient populations account for many differences in prevalence. The higher the MCV cutoff, the lower the prevalence of macrocytosis. Prevalence is higher with age. Most studies show higher prevalence of macrocytosis in males compared to females.

About 20%. Learn more here.

30-45% of patients

RBC transfusion at Hb level of < 7 g/dL (70 g/L) with a target Hb of 7-9 g/dL (70-90 g/L). Transfusion trigger should not exceed 90 g/L in most critically ill patients.

AABB recommendations in 2016:

For patients with stable cardiovascular disease who are hemodynamically stable, transfuse RBCs at Hb level of ≤ 8 g/dL (80 g/L).

AABB recommendations in 2016:

AABB recommendations 2022:

Consider treatment of symptomatic anemia with red cell transfusion to minimize symptoms; transfusion usually required when Hb is < 6 g/dL (60 g/L).

For patients having orthopedic or cardiac surgery and are hospitalized and hemodynamically stable, transfuse at Hb level ≤ 8 g/dL (80 g/L).

AABB recommendations in 2016:

0.1 % to 0.3 % per year. A nearly 7-fold significantly higher relative risk of gastric cancer in patients with vs without pernicious anemia.

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0.4–0.7% per year. Learn more here.

Acute chest syndrome

Anemia of inflammation

> 24 hours after transfusion.

Within 24 hours of transfusion or during transfusion.

Eculizumab, a monoclonal anti-C5 antibody that blocks the entry of C5 into C5 convertase.

141 Legendre CM, Licht C, Muus P, et al. Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome. N Engl J Med 2013; 368: 2169–81. 142 Licht C, Greenbaum LA, Muus P, et al. Efficacy and safety of eculizumab in atypical hemolytic uremic syndrome from 2-year extensions of phase 2 studies. Kidney Int 2015; 87: 1061–73. 143 Fakhouri F, Hourmant M, Campistol JM, et al. Terminal complement inhibitor eculizumab in adult patients with atypical hemolytic uremic syndrome: a single-arm, open-label trial. Am J Kidney Dis 2016; 68: 84–93. 144 Fakhouri F, Hourmant M, Campistol JM, et al. Eculizumab inhibits thrombotic microangiopathy, and improves renal function in adult atypical hemolytic uremic syndrome patients: 1-year update. J Am Soc Nephrol 2014; 25: 751A

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  • Prodromic phase including minor behavioral changes such as:
    • Anxiety
    • Restlessness
    • Insomnia
  • Severe abdominal pain, but this pain might also be felt in the back or thighs.
  • Nausea, vomiting, and constipation are common.
  • Symptoms of increased sympathetic activity, including:
    • Tachycardia
    • Excess sweating
    • Hypertension

Physical exam usually normal.

Labs may show hyponatremia.

Urine may be red or dark-colored.

Most acute attacks last for no longer than 1 or 2 weeks.

Learn more here.

300 mL to 400 mL

According to a Circular prepared jointly by AABB, the American Red Cross, America’s Blood Centers, and the Armed Services Blood Program:

Depending upon the collection system used, a single whole blood donation typically contains either 450 mL (+/- 10%) or 500 mL (+/- 10%) of blood collected from allogeneic blood donors. After plasma is removed, the resulting component is RBCs, which has a hematocrit between 65% to 80% and a usual volume between 225 mL and 350 mL. Red Blood Cells additive solutions (AS) may be mixed with the red cells remaining after removal of nearly all of the plasma to extend the shelf life (see Table 2). The typical hematocrit of AS RBCs is 55% to 65%, and the volume is approximately 300 to 400 mL.

Acute pulmonary edema due to volume overload from transfusion. Usual onset within 1-2 hours of transfusion. Risk factors include transfusion of large volumes of components or high flow rates. Treatment is supportive and may include lasix, and rarely therapeutic phlebotomy.

According to Nareg Roubinian, TACO is pulmonary edema primarily related to circulatory overload with criteria developed by the National Healthcare Safety Network including 3 or more of the following within 6 hours of transfusion:

  • Acute respiratory distress
  • Radiographic pulmonary edema
  • Elevated central venous pressure
  • Evidence of left heart failure
  • Elevated B-type natriuretic peptide (BNP)
  • Positive fluid balance

According to the AABB, TACO is defined as new onset or exacerbation of 3 or more of the following within 12 hours of cessation of transfusion:

  • Elevated brain natriuretic peptide (BNP) or NT-pro BNP relevant biomarker.
  • Evidence of cardiovascular system changes not explained by underlying medical condition (Elevated central venous pressure, evidence of left heart failure including development of tachycardia, hypertension, widened pulse pressure, jugular venous distension, enlarged cardiac silhouette and/or peripheral edema).
  • Evidence of fluid overload.
  • At least 1 of the following:
    • Evidence of acute or worsening respiratory distress (dyspnea, tachypnoea, cyanosis and decreased oxygen saturation values in the absence of other specific causes) and/or,
    • Radiographic or clinical evidence of acute or worsening pulmonary edema (crackles on lung auscultation, orthopnea, cough, a third heart sound and pinkish frothy sputum in severe cases).
From Hematology Am Soc Hematol Educ Program. 2018;2018:585-594.

Form of acute lung injury caused by donor leukocyte antibodies (occasionally in recipient) and other leukocyte activating agents in plasma-containing components including whole blood, RBCs, platelets, cryoprecipitate, and fresh frozen plasma. Symptoms arise within 6 hours of transfusion and typically resolve after 48-96 hours. Treatment is supportive.

The Canadian Consensus Criteria defines TRALI as acute pulmonary edema after transfusion in the absence of circulatory overload or alternate acute respiratory distress syndrome (ARDS) risk factors:

According to the AABB, TRALI is defined as:

  • No evidence of acute lung injury (ALI) prior to transfusion, and
  • ALI onset during or within 6 hours of cessation of transfusion, and
  • Radiographic evidence of bilateral infiltrates, and
  • No evidence of left atrial hypertension (i.e., circulatory overload), and
  • Hypoxemia defined by any of these methods:
    • PaO2/FiO2 less than or equal to 300 mmHg
    • Oxygen saturation less than 90% on room air
    • Other clinical evidence
From Hematology Am Soc Hematol Educ Program. 2018;2018:585-594.

Increased iron intake sustained over a period of time as a result of multiple red blood cell (RBC) transfusions which may be exacerbated by increased absorption through the gastrointestinal tract.

Hct by microhematocrit centrifugation is slightly higher owing to the effect of trapped plasma.

Unexplained anemia of the elderly (UAE) is an entity characterized by a hypoproliferative normocytic anemia that is not due to the nutritional deficiency, chronic kidney disease or inflammatory disease, and in which the erythropoietin response to anemia is blunted.

Learn more here.

First-line testing:

  • Complete blood count
  • Peripheral blood smear
  • Renal function
  • Liver function
  • Arterial oxygen saturation
  • Carboxyhemoglobin
  • Serum ferritin
  • Serum erythropoietin:
    • A low erythropoietin level (< 2.9 mU/mL) specific (92%) and moderately sensitive (64%) for the diagnosis of polycythemia vera.
    • A high erythropoietin level (> 15.1 mU/mL) specific (98%) but had poor sensitivity (47%) for the diagnosis of secondary erythrocytosis.
  • Jak2 mutational analysis (peripheral blood) – based on the pretest probability of polycythemia vera (PV):
    • In the primary care setting, where the probability of PV is low, clinical evaluation for secondary causes of erythrocytosis paired with a high erythropoietin level can rule out PV in most patients.
    • In hematology clinics, where the probability of PV is higher, erythropoietin level and JAK2 V617F mutation testing are done concurrently.
    • Patients with a low or normal erythropoietin level and no JAK2 V617F mutation are further evaluated with JAK2 exon 12 mutation testing (on peripheral blood or marrow aspirate, based on local practice) and a bone marrow biopsy.

Second-line testing:

  • When no diagnosis is made, selected patients with onset of erythrocytosis at a young age or compatible family history should undergo testing for high-oxygen-affinity hemoglobins, and gene sequencing for mutations involving the erythropoietin receptor or oxygen-sensing pathways.
  • Investigations for secondary erythrocytosis should be symptom directed and may include:
    • Chest radiography
    • Overnight oximetry for suspected sleep apnea
    • Pulmonary function tests for hypoxic lung disease
    • Venous blood gas sampling (carboxyhemoglobin level)
    • Echocardiography to rule out right to left cardiac shunting
    • Abdominal–pelvic imaging can help exclude an erythropoietin-producing tumor or conditions associated with local renal hypoxia.
    • Neuroimaging to rule out meningioma or cerebellar hemangioblastoma should be ordered for patients with unexplained neurologic symptoms as these tumors have been associated with autonomous erythropoietin production.
CXR, chest X ray.

Learn more here.

  • Electrical impedance (Coulter principle) 
  • Optical light measurements
    • Optical absorbance
    • Optical light scatter
    • Fluorescence
  • Cyanmethemoglobin measurement of hemoglobin


About 50%

About 70-80%

Reported mean daily iron absorption 6% for male adults and 13% for nonpregnant female adults in their childbearing years. Amounts to 1-2 mg/day (increasing to 6 mg in the third trimester of pregnancy).

Renal failure requires prompt initiation of dialysis in more than 50% of cases regardless of the cause of hemolytic uremic syndrome, and in more than 75% of adults with atypical hemolytic uremic syndrome.

Learn more here.

40–60% of patients.

Learn more here.


10%-20% of patients. Learn more here.

>90% of such patients have evidence for a clonal expansion of kappa-positive B cells and a monoclonal IgM paraprotein. Learn more here.

About 1%

About 25%-35%. Learn more here.

About 30%

Iron deficiency is estimated to account for about 50% of all cases of anemia in pregnant and nonpregnant female adults.


Purple top tube, containing the anticoagulant EDTA (a powder sprayed on the wall of the tube).

IgM, reacting optimally between 0 and 4 degrees C. Learn more here.

Homozygous sickle cell disease (HbSS) and sickle beta0 thalassemia. .

Both markers are highly sensitive, but MMA is more specific (for example, homocysteine levels may also be increased in patients with folate deficiency). MMA values considered high vary from 0.28 to 0.75 mcmol/L.

2014 British Committee for Standards in Haematology guidelines for the diagnosis and treatment of cobalamin and
folate disorders:

Learn more here.

Intrinsic factor antibodies are more specific (98-99% vs. 50%) but less sensitive (40-60% vs. 80-90%) than antiparietal antibodies.

In the mid-1950s when Wallace Coulter patented his technique for blood cell counting (termed the Coulter principle).

Learn more here.

Humans have no mechanisms to excrete iron. Iron is normally lost through:

  • Skin desquamation
  • Sweat – sweat contains up to 0.3 mg iron/L
  • Gut
  • Menstruation
  • Pregnancy

Terminal ileum.

Anti-parietal cell antibodies, which target the gastric enzyme H+/K+ATPase proton pump. Learn more here.

Louis Diamond and Kenneth Blackfan, who first described the disorder in 1938 (Diamond LK, Blackfan KD. Hypoplastic Anemia. American Journal of Diseases of Children. 1938;56:464–467).

About 90% of cases reported in female adults, mean age at diagnosis of 47 years.

Robert S. Evans, first author on paper (titled “Primary thrombocytopenic purpura and acquired hemolytic anemia: evidence for a common etiology”) that first described the syndrome in 1951.

V. Koneti Rao wrote:

Known to his colleagues and friends as Bud Evans, he was a native Seattleite. Unfortunately, Evans was killed in a tragic car accident on Mercer Island in 1974 at the young age of 62.

Henry Stanley Plummer (1874–1936) and Porter Paisley Vinson (1890–1959) who were physicians on the staff of the Mayo Clinic. Learn more here.

Because megaloblastic red cell precursors are destroyed in the bone marrow (ineffective erythropoiesis) and these immature cells contain hemoglobin, LDH and AST.

Because of residual RNA

Arrow, points to a polychromatophilic cell, which corresponds to a reticulocyte.

White blood cells

Persons of African descent often have lower normal neutrophil counts, with ANC <1.5 × 109/L occurring in about 4.5% of black participants in one U.S. survey, and associated with the Duffy negative blood group. Learn more here.

Absolute neutrophil count (ANC) less than 1.5 × 109/L lasting for more than 3 months. Learn more here.

Constitutional/ethnic neutropenia is not associated with clinical manifestations. it is considered a normal variant (adaptive/protective in malaria-endemic regions of the world). It does not require any treatment, e.g., antimicrobial prophylaxis or G-CSF.

Lymphocyte count > 3.5-4.5 × 109/L

Absolute neutrophil count (ANC) ≤ 1.5 × 109/L in adults. Learn more here.

  • Mild 1-1.5 × 109/L; does not impair host defense.
  • Moderate 0.5-1 × 109/L; slight increased risk of infection if other arms of immune system also impaired.
  • Severe < 0.5 × 109/L; increased risk of infection in most patients.
  • Agranulocytosis ≤ 0.2 × 109/L; risk of severe, life-threatening infections.

Learn more here.

1.6 billion leukocytes per kilogram body weight; more than half are neutrophils.


  • Arthralgia
  • Bone and back pain
  • Muscle spasms
  • Musculoskeletal pain
  • Pain in extremity
  • Splenomegaly
  • Epistaxis
  • Chest pain
  • Diarrhea
  • Hypoesthesia
  • Alopecia
  • Familial or congenital (rare)
  • Acquired
    • Primary (clonal)
      • Myeloproliferative neoplasms (MPN)
      • Myelodysplastic syndrome (MDS)
      • MDS/MPN overlap syndromes
      • Acute myeloid leukemia (AML)
      • Mastocytosis
      • Myeloid/lymphoid neoplasms with eosinophilia (rearrangement of PDGFRAPDGFRB, or FGFR1, or with PCM1-JAK2)Secondary (reactive)
    • Secondary (reactive)
      • Allergies
      • Helminth infections
      • Drug reactions
      • Autoimmune disorders
      • Cancer
      • Lymphocyte variant hypereosinophilia syndrome (HES)

Learn more here.

NAN, neonatal alloimmune neutropenia; NIN, neonatal isoimmune neutropenia,; SCN, severe congenital neutropenia; SLE, systemic lupus erythematosus; RA, rheumatoid arthritis

Neutrophils, basophils, and eosinophils

  • Decreased production
  • Increased retention in bone marrow (decreased release into blood)
  • Increased migration to sites of inflammation
  • Increased apoptosis
  • Increased destruction and clearance by macrophages
  • Splenic sequestration

A group of chronic myeloid disorders characterized by hematopoietic stem cell-derived clonal myeloproliferation.

Neutrophils, basophils, and eosinophils

  • Anemia (21%-39% of patients)
    • Typically normocytic, normochromic)
    • Rarely acquired hemolytic syndrome from hypophosphatemia accompanying anorexia nervosa (e.g., during the refeeding process)
  • Leukopenia (29%-36% of patients)
    • Mild neutropenia
    • Lymphocytopenia
  • Thrombocytopenia (5-11% of patients)
  • Acanthocytes on peripheral smear
  • Gelatinous transformation or serous atrophy on bone marrow exam

Learn more here.

Learn more here.
Meds, medications; MM, multiple myeloma; MDS, myelodysplastic syndrome; mets, metastases; DIC, disseminated intravascular coagulation.
See graphic.

Another perspective:

  • Chronic myeloid leukemia (CML) (BCR-ABL1+)
  • Philadelphia chromosome-negative (BCR-ABL) MPN:
    • Polycythemia vera (PV)
    • Primary myelofibrosis (PMF)
      • PMF, prefibrotic/early stage
      • PMF, overt fibrotic stage
  • Essential thrombocythemia (ET)
  • Chronic neutrophilic leukemia (CNL)
  • Chronic eosinophilic leukemia, not otherwise specified (NOS)
  • MPN, unclassifiable

Learn more here.

Döhle bodies bodies, toxic granulation and vacuolization

Reactive (secondary):

  • Viral, bacterial, or parasitic infection
  • Vaccinations
  • Connective tissue disease
  • Smoking
  • Postsplenectomy state

Clonal (primary):

  • Chronic lymphocytic leukemia (CLL)
  • Certain B-cell and T-cell leukemia/lymphomas

Reactive (secondary):

  • Viral or bacterial infection
  • Corticosteroids
  • Malignancy
  • Postsplenectomy state
  • Autoimmune disorders (such as inflammatory bowel disease or sarcoidosis)
  • Vasculitides

Clonal (primary):

  • Monocytic leukemia
  • Chronic myelomonocytic leukemia
  • Mastocytosis
  • Infections
    • Viral infections (most common cause)
      • HIV
      • Cytomegalovirus
      • EBV
      • HPV6
      • Parainfluenza virus
      • Parvovirus B19
    • Bacterial infections, especially in cases of:
      • Overwhelming infection (sepsis)
      • Salmonella
      • Brucellosis
    • Malaria
  • Certain drugs – can occur at any time during treatment; most common culprits include:
    • Chemotherapy agents
    • Antiepileptics (e.g. valproate, carbamazepine)
    • Antipsychotics (e.g. clozapine)
    • Anti-thyroid drugs
    • Antibiotics
    • Anti-inflammatory drugs

Myelodysplastic syndrome

Myeloproliferative neoplasm

Differential counts of neutrophils, eosinophils, basophils, lymphocytes, and monocytes, typically performed by modern automated hematology analyzers.

A band neutrophil is a young neutrophil with deeply indented nucleus. The nucleus is indented to more that half the distance to the farthest nuclear margin. Chromatin is consistently present between edges of nuclear membrane, but in no area is it condensed to a single filament. Normally comprise < 10% of circulating white cells. Increased numbers in left shift (as occurs with inflammation and infection) and myeloproliferative neoplasms.

From Shutterstock, with permission.
Peripheral smear showing band neutrophil in center. From Shutterstock, with permission.

Döhle bodies appear as single or multiple blue or gray-blue inclusions of variable size (0.1 to 5.0 μm) and shape (round or elongated or crescent shaped) in the cytoplasm of neutrophils, bands, or metamyelocytes. They are often found in the periphery of the cytoplasm, near the cell membrane. Seen in conditions associated with increase cytokine release such as infection, burns, trauma, and administration of G-CSF.

Peripheral smear showing Dohle body (arrow) in a neutrophil

A leukemoid reaction is defined by a leukocyte count greater than 50,000 cells/μL, caused by reactive causes outside the bone marrow. Learn more here.

4-11 x 109/L

Smudge cells are remnants of fragile lymphocytes that are generated during preparation of peripheral smear. They lack any identifiable cytoplasmic membrane or nuclear structure. They contain dense nuclear material and or chromatic strands. They are characteristic of chronic lymphocytic leukemia.

Neutropenia that is acquired in adulthood but eludes a specific diagnosis is termed chronic idiopathic neutropenia (CIN). It is a diagnosis of exclusion that can only be made after a thorough and unrevealing search for other causes, including negative testing for autoimmune disease and nutritional deficiency and a normal bone marrow examination with normal cytogenetics. Its pathogenesis is unknown.

Learn more here.

Benign, stable course often in middle-aged women with rare evolution to myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Diagnosis of exclusion. Term is often used synonymously with autoimmune-mediated neutropenia since there are no definitive tests to diagnose the latter.

Mild, chronic neutropenia, usually with an ANC >1000 in a patient with no history of recurrent infections. Affects mostly individuals of African or Arabic ancestry, but also seen in people from the Middle East or Crete. Learn more here.

Cyclic neutropenia (CN) is a rare autosomal dominant disease characterized by episodes of self-limited neutropenia that recur every 2 to 5 weeks. The cycles are of varying length but are very consistent within each patient. Unlike SCN, there is no increased risk of developing AML. CN results from mutations in ELANE.

Learn more here.

Persistent blood eosinophil count >1.5 x 109/L (on 2 examinations over ≥ 1 month without evidence of organ damage). Learn more here.

White blood cell count (WBC) > 100 x 109/L, usually seen in leukemias and myeloproliferative disorders, though may rarely occur as a reactive condition.

LeukocytosisWhite blood cell (WBC) count > 11 × 109/L.
Leukemoid reactionIncreased WBC count (typically > 50-100 × 109/L) that occurs in response to reactive causes.
HyperleukocytosisWBC > 100 × 109/L, usually found in leukemias and myeloproliferative disorders.
LeukoerythroblastosisImmature neutrophil precursors (with or without leukocytosis) and nucleated red blood cells in peripheral blood, indicative of severe disruption of the marrow by overwhelming infection, myelofibrosis, or bone marrow invasion due to malignancy.

A benign condition diagnosed in young adults, with some resemblance to autoimmune neutropenia in children and the so-called ethnic neutropenia:

  • Occurs in young adults.
  • Because of the lack of any definitive tests, the diagnoses “autoimmune neutropenia” and “idiopathic neutropenia” are used nearly synonymously.
  • Neutropenia may be mild, moderate or severe; may be associated with profound reduction in neutrophil count (< 0.5 x 109/L).
  • Usually detected incidentally on a complete blood count.
  • Those with severe neutropenia may develop recurrent fevers, upper respiratory infections and skin infections, but the infections are readily treated with antibiotics in most cases.
  • The ANC may normalize during infections.
  • Rarely associated with other organ-specific autoimmune diseases.
  • Lasts several years or even life-long, with a female predominance (80% women).

Learn more here.

Immature neutrophil precursors – in absence or presence of elevated white count – and nucleated red blood cells (RBCs) in the peripheral blood, indicative of severe disruption of the marrow by overwhelming infection, myelofibrosis, or bone marrow invasion due to cancer. Tear drop shaped RBCs are also often present. Learn more here.

Intravascular accumulation of white blood cells (WBCs) causing obstruction of blood flow in patients with hyperleukocytosis (defined as WBC count >100 x 109/L), especially those with acute leukemia, in which the white cells are “stickier” compared to reactive causes or those with chronic lymphocytic leukemia (CLL). May lead to organ compromise. Learn more here.

A heterogeneous group of clonal disorders characterized by ineffective hematopoiesis leading to peripheral blood cytopenias and an increased risk of transformation to acute myeloid leukemia.

Reactive (polyclonal) eosinophilia secondary to malignancy

  • A heterogeneous syndrome, caused by inherited mutations in several neutrophil-specific genes, most commonly the primary granule protein gene neutrophil elastase (ELANE).
  • Characterized by agranulocytosis and recurrent, severe infections that begin during infancy.
  • 10% to 30% lifetime risk of developing acute myelogenous leukemia.

learn more here.

Homozygosity of the single nucleotide polymorphism (SNP) rs2814778 located in the promoter region of the Duffy Antigen Receptor for Chemokines (DARC) also named Atypical chemokine receptor 1 (ACKR1) gene. This variant codes the Duffy negative [Fy(a-b-)] blood group. The Duffy positive phenotype is found in only 0.2% of Africans and 99.3% of Europeans. Duffy null polymorphism associated with protection against invasion of red blood cells by Plasmodium vivax malaria. Mechanism of lack of DARC and associated neutropenia unknown.

According to Donadieu et al:

Although this clinically insignificant variant most often seen in those of African descent has historically been called ‘benign ethnic neutropenia,’ we feel this name is problematic as it implies that ethnicity is causative and that this is a disease that requires intervention. We advocate for an alternative name such as chronic benign neutropenia, Duffy null associated neutrophil count, or typical neutrophil count with Fy (a-b-) status that reflects the genetic underpinning of this variant and highlights that it is not a disease state. Consensus has yet to be reached for an alternative name or expected ranges of normal neutrophil counts.

Autosomal dominant disorder usually caused by mutation in primary granule protein gene elastase, neutrophil expressed (ELANE, formerly ELA2), which encodes neutrophil elastase.

  • Autosomal dominant causes include mutations in:
    • ELANE
    • GFI1, which encodes transcriptional repressor oncoprotein GFI1 thus repressing CEBPACEBPE and ELANE, important regulators of myeloid differentiation and neutrophil function
    • CSF3R
  • Autosomal recessive causes include mutations in:
    • HAX1, which encodes an antiapoptotic gene (also called Kostmann syndrome)
    • G6PC3, which encodes a neutrophil-specific catalytic subunit of glucose-6-phosphatase
    • VPS45
    • JAGN1
    • CSF3R
  • Unidentified genetic cause in up to 30% of SCN patients.

Absolute neutrophil count of 0.2 × 109/L or less

Basophil count > 0.1 x 109/L

White cell count > 11 x 109/L

Monocyte count > > 0.8-1.0 × 109/L

Neutrophil count > 7-7.7 × 109/L

Reactive (secondary):

  • Drug reactions
  • Allergy/hypersensitivity reaction
  • Infections (especially tissue-invasive parasites, such as strongyloides)
  • Cancer
  • Sarcoidosis
  • Connective tissue diseases
  • Adrenal insufficiency
  • Pulmonary diseases such as eosinophilia pneumonia

Clonal (primary):

  • Chronic eosinophilic leukemia
  • Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRAPDGFRB, or FGFR1, or with PCM1-JAK2
  • Other acute and chronic primary bone marrow processes such as myeloproliferative neoplasms

Reactive (secondary):

  • Infection
  • Chronic inflammation
  • Smoking
  • Stress
  • Obesity
  • Drugs, for example:
    • Corticosteroids
    • Beta-agonists
    • Lithium
    • Epinephrine
  • Endocrine disorders:
    • Hypercortisolism
    • Thyroid storm
    • Pre-eclampsia
  • Post-splenectomy state
  • Bone marrow stimulation
  • Nonhematologic malignancy
  • Inherited disorders

Clonal (primary):

  • Chronic neutrophilic leukemia
  • Chronic myelogenous leukemia
  • Essential thrombocytosis (ET)
  • Polycythemia vera (PV)
  • Blood eosinophilia is defined as peripheral blood eosinophil count > 0.5 × 10 9/L.
  • Blood hypereosinophilia is persistent eosinophil count > 1.5 × 109/L on 2 examinations over ≥ 1 month without evidence of organ damage.
  • Hypereosinophilic syndrome is hypereosinophilia of any cause (reactive or clonal) associated with clear evidence of hypereosinophilia-related organ damage.

Learn more here.

  • Defined as immature neutrophil count (myelocytes + metamyelocytes + promyelocytes)/total neutrophil count.
  • Used as an indicator of a granulocyte left shift.

In adults, neutropenia is estimated to occur in about 1% of the non-African population and 5–8% of those of African
origin. Read more here.

Congenital neutropenia is extremely rare, with an estimated prevalence of 10-5. Learn more here.

Toxic granulation is the presence of large purple or dark blue cytoplasmic granules (primary granules) in neutrophils, bands, and metamyelocytes. The granules have increased staining density compared to normal neutrophils. Seen in conditions associated with increase cytokine release such as infection, burns, trauma, and G-CSF administration.

Only 1–5% of the total granulocytes in the body are circulating. Read more here.

Neutropenia reported to occur in up to 50% of patients with SLE.

Counts may vary considerably over short periods of time, associated with:

  • Activity
  • Exercise
  • Eating
  • Time

Learn more here.


Typically 5-10 days. Learn more here.

No. Normal complement concentrations do not exclude aHUS because low levels of circulating C3 have low sensitivity (about 30% of patients with aHUS), whereas high concentrations of circulating C5a and soluble C5b-9 might have insufficient specificity.

Learn more here.

Yes, especially in primary thrombocytosis, because platelet glycoprotein 1b binds to circulating von Willebrand factor, leading to acquired von Willebrand syndrome.

No, the pathogenesis of iron deficiency-associated thrombocytosis remains unclear, but may involve increased commitment of bipotential (erythroid/megakaryocytic) progenitor cells to the megakaryocytic lineage. Learn more here.

Yes, they are 20-25% lower in individuals with type O blood group. 14% of individuals with type O blood have vWF levels ≤ 50 units/dL. Learn more here.

According to the 2019 ASH guideline, <30 x 109/L:

According to the 2019 International Consensus Report, <20-30 x 109/L:

ADAMTS13 activity level

No. In unconfirmed aHUS, serum/plasma complement factor levels may suggest the diagnosis but they are not diagnostic.

Yes, and in fact they are now recommended as an option in the latest American Society of Hematology (ASH) guideline, especially for those who are not at high risk of bleeding and who do not have extensive clot burden:

At minimum, all critically ill non-bleeding patients with DIC should receive prophylactic anticoagulation for venous thromboembolism.

Regarding therapeutic doses of heparin, the 2013 ISTH harmonization guideline states:

Anticoagulant treatment may be a rational approach based on the notion that DIC is characterized by extensive activation of coagulation. Although experimental studies have shown that heparin can at least partly inhibit the activation of coagulation in DIC, there are no RCTs demonstrating that the use of heparin in patients with DIC results in an improvement in clinically relevant outcomes… therapeutic doses of heparin should be considered in cases of DIC where thrombosis predominates (low quality evidence). The use of low molecular weight heparin (LMWH) is preferred to the use of unfractionated heparin (UFH) in these cases (low quality evidence).

Yes! Proposed mechanisms include:

  • Formation of platelet-white cell complexes
  • Direct effect of pathogens on platelet activation and aggregation
  • Hemophagocytosis
  • Reduced platelet production

Learn more here.

Thrombocytopenia is absent at presentation in 15–20% of patients.

Learn more here.

Patients with type 2B vWD may have thrombocytopenia. Learn more here.

No, they are not different between the two conditions.

No significant difference in thrombopoietin (TPO) levels was found between the two groups of patients, indicating that serum TPO levels cannot differentiate between primary and reactive thrombocytosis. No significant correlation was found between platelet count and TPO levels in either ET-PV or reactive thrombocytosis. Source.

Learn more here.

Caplacizumab does not affect ADAMTS levels or ADAMTS13 antibody production. It is an anti–von Willebrand factor humanized, bivalent variable-domain-only immunoglobulin fragment that inhibits interaction between von Willebrand factor multimers and platelets.

Yes, it is much more common in later stages of cirrhosis (about 5% prevalence with I-IV fibrosis vs. 65% in patients with stage III-IV fibrosis). Learn more here.

CCI = posttransfusion count increment (CI; posttransfusion platelet count – pretransfusion platelet count) × body surface area (in m2)/number of platelets transfused

See calculator.

Posttransfusion platelet count – pretransfusion platelet count

By apheresis or from whole blood by platelet-rich plasma or buffy coat methods.

They are pinched off from proplatelet tips and released into the circulation. Learn more here.

They are stored in gas-permeable storage bags with gentle agitation at 20-24 degrees C (68-75.2 degrees F).

2-4 × 0.5 micrometers with mean volume of 7-11 fL.

15%-20% of patients presenting with acute lymphoblastic leukemia, > 90% of patients presenting with acute promyelocytic leukemia.

About 1%

Over 95% of patients with DIC have thrombocytopenia.

Occurs in about 50-60% of such patients.

About 8%-68% of patients at time of admission, up to 50% of patients during stay in ICU. Learn more here.

Thrombocytosis occurs in about 10-15% of patients with iron deficiency anemia. Learn more here.

They block platelet aggregation by inhibiting fibrinogen binding to glycoprotein GPIIb/III on the platelet surface.

DDAVP 0.3 mcg/kg IV in 30-50 mL normal saline over 30 minutes. May be repeated 12-24 hours after first dose, depending on how well the patient responds, but no more than 2-3 doses should be given in order to avoid tachyphylaxis.

Steroids decrease platelet clearance and increase platelet production. Also, steroids may reduce bleeding, independent of their effect on platelet counts, by a direct stabilizing effect on blood vessels. Learn more here.

1 unit vWF:RCo/kg infused will result in recovery of 1.5-2 units vWF:RCo/dL in adults; 50 units vWF:RCo/kg will give a recovery of 75-100 units vWF:RCo/dL.

Direct toxic effect on the bone marrow. Learn more here.

Aspirin inhibits cyclooxygenase 1 (COX1), thereby decreasing production of thromboxane A, a major mediator of platelet activation.

DDAVP increases the release of vWF and factor VIII from endothelial cell stores by releasing vWF from cytoplasmic organelles called Weibel-Palade bodies.

Removes autoantibodies and replenishes ADAMTS13 levels.

Rarely below 30-40 × 109/L

70%-80% of cases

Thrombosis occurs in one-third to one-half of patients with HIT. It may occur in veins, arteries or microvessels.

Platelet count < 100 × 109/L in absence of other causes of thrombocytopenia.

From the 2019 International Consensus Report

aPTT; adjust to 1.5-3.0 times baseline.

aPTT; adjust to 1.5-2.5 times baseline.

DDAVP may be administered IV, subcutaneously, or by nasal spray.

No one laboratory test is specific for DIC. Clinical practice guidelines recommend using a clinical scoring system, such as the ISTH scoring system, which includes consideration of the platelet count, D-dimers, fibrinogen and the prothrombin time.

Learn more here.

Based on clinical presentation (thrombocytopenia and/or thrombosis in temporal association with heparin therapy without other obvious causes) plus presence of platelet-activating antiplatelet factor 4 (PF4)/heparin antibodies. Clinical prediction scores, especially the 4T score, are helpful in estimating the pretest probability of HIT and determining whether heparin should be discontinued and if further testing for antibodies should be carried out.

Low Corrected Count Increment (CCI) < 1 hour after transfusion suggests immune-mediated platelet refractoriness. Most studies define refractoriness as a CCI of <5,000 after 2 sequential transfusions. However, a CCI of <7,500 or a PPR of <30% are also accepted values. Learn more here.