Labs

The following is the complete blood count (CBC) the day you see the patient:
WBC (109/L) | Hb (g/dL) | MCV (fL) | MCHC (g/dL) | RDW-SD (fL) | PLT (109/L) |
---|---|---|---|---|---|
9.4 | 8.9 | 86 | 30.1 | 64.3 | 240 |
What’s what: WBC, white blood cell count; Hb, hemoglobin; MCV, mean cell volume; MCHC, mean cellular hemoglobin concentration; RDW-SD, red cell distribution width-standard deviation; platelets, PLT; Normal values: WBC 5-10 x 109/L, RBC 4-6 x 1012/L, Hb 12-16 g/dL, Hct 35-47%, MCV 80-100 fL, MCHC 32-36 g/dL, RDW-SD < 45 fL, platelets (PLT) 150-450 x 109/L
The diagnostic algorithm for anemia begins with a mean cell volume and reticulocyte count:


The following was the patient’s reticulocyte count:





The absolute reticulocyte count, which is what we want to focus on is:
0.45 x 1012/L = 450 x 109/L
Therefore, the patient has a hyperproliferative normocytic, normochromic anemia.
The patient was told she has thalassemia trait. However, her mean cell volume (MCV) is 86 fL. Does the normal MCV rule out thalassemia? If not, why?
We will take a look at the peripheral smear shortly. For now, consider the following questions:
If the patient has hemolytic anemia, what might you expect to find?
It is the indirect bilirubin that increases in hemolysis.
The following are the results of the hemolysis screen:





Hemolytic anemia may be classified in several ways. One classification is intravascular vs. extravascular. The isolated elevation in indirect bilirubin without any increase in AST and LDH is most consistent with:
Now we can conclude that the patient has a hemolytic anemia, most likely congenital given her age and long history of anemia. What are possible causes of congenital hemolytic anemia?
The following table includes the more common causes of congenital hemolytic anemia. Fill in the peripheral smear findings (in addition to polychromatophilia from reticulocytosis) and relevant diagnostic tests.
Condition | Peripheral smear | Additional tests |
---|---|---|
Sickle cell disease | ||
Thalassemia minor | ||
Hereditary spherocytosis | ||
Hereditary elliptocytosis | ||
G6PD deficiency | ||
Pyruvate kinase deficiency |
The following table includes the more common causes of congenital hemolytic anemia. Fill in the peripheral smear findings (in addition to polychromatophilia from reticulocytosis) and relevant diagnostic tests.
Condition | Peripheral smear | Additional tests |
---|---|---|
Sickle cell disease | Sickle cells, nucleated red cells, Howell-Jolly bodies | Hemoglobin electrophoresis |
Thalassemia minor | Microcytic red cells | Hemoglobin electrophoresis, DNA sequencing |
Hereditary spherocytosis | Spherocytes | EMA binding, osmotic fragility |
Hereditary elliptocytosis | Elliptocytes | Osmotic gradient ektacytometry |
G6PD deficiency | Pitted red cells | Enzyme activity |
Pyruvate kinase deficiency | Acanthocyte-like cells | Enzyme activity, DNA sequencing |
The following is similar to the peripheral smear from the patient:
What is the next test you would like to perform?
Osmotic fragility test
Specimens for red cell osmotic fragility tests are anticoagulated with EDTA. Osmotic lysis is performed using sodium chloride (NaCl) solution, 0.50 g/dL. An incubated fragility test is performed following 24-hour incubation at 37 degrees C at the following NaCl concentrations: 0.60, 0.65, and 0.75 g/dL. Results are reported and interpreted.
Spherocytes are osmotically fragile cells that rupture more easily in a hypotonic solution than do normal RBCs. Because they have a low surface area: volume ratio, they lyse at a higher osmolarity than do normal red cells. Cells that have a larger surface area: volume ratio, such as target cells or hypochromic cells are more resistant to lysing. After incubation, an increase in hemolysis is seen in spherocytes. Hereditary spherocytosis typically has greater number of spherocytes than other causes of spherocytosis. Therefore, the degree of lysis is usually more pronounced, but this is not always the case. Some rare disorders can also cause marked fragility and hereditary spherocytosis cases can display moderate fragility.
These are the results of the patient’s osmotic fragility study:


How would you interpret these data?
The following is the interpretation of this patient’s osmotic fragility test:




Collectively, the data support a diagnosis of hereditary spherocytosis.
What do you expect the mean cell hemoglobin concentration to be in patients with hereditary spherocytosis?
The increased mean cell hemoglobin concentration is evident from the loss of central pallor in spherocytic cells. Consider the following schematic of red cells. Which of the following questions is/are correct?


A recent study examining red cell indices in patients with various hemoglobinopathies found that hereditary spherocytosis is indeed associated with an elevated mean corpuscular hemoglobin concentration (MCHC). It is interesting to note that the mean cell volume (MCV) is not decreased in patients with hereditary spherocytosis. One might expect that red cells that lose surface membrane would become smaller, and indeed they appear smaller on peripheral smears. It is possible that the normal MCV reflects a population of smaller than normal spherocytes and a population of larger reticulocytes.






Here again is the patient’s complete blood count.
WBC (109/L) | Hb (g/dL) | MCV (fL) | MCHC (g/dL) | RDW-SD (fL) | PLT (109/L) |
---|---|---|---|---|---|
9.4 | 8.9 | 86 | 30.1 | 64.3 | 240 |
What’s what: WBC, white blood cell count; Hb, hemoglobin; MCV, mean cell volume; MCHC, mean cellular hemoglobin concentration; RDW-SD, red cell distribution width-standard deviation; platelets, PLT; Normal values: WBC 5-10 x 109/L, RBC 4-6 x 1012/L, Hb 12-16 g/dL, Hct 35-47%, MCV 80-100 fL, MCHC 32-36 g/dL, RDW-SD < 45 fL, platelets (PLT) 150-450 x 109/L
Note that the mean corpuscular hemoglobin concentration (MCHC) is actually on the low side. As we saw from the last slide, this is not typical for hereditary spherocytosis.
As we will see in About the Condition, hereditary spherocytosis can be classified according to its clinical severity:
% Cases | Hemoglobin (g/dL) | Reticulocytes (%) | Bilirubin (mg/dL) | |
---|---|---|---|---|
HS trait | N/A | Normal | Normal | Normal |
Mild HS | 20-30% | 11-15 | 3-6 | 1-2 |
Moderate HS | 60%-75% | 8-12 | > 6 | > 2 |
Severe HS | 5% | 6-8 | > 10 | > 3 |
Let’s look at this patient’s parameters again:
WBC (109/L) | Hb (g/dL) | MCV (fL) | MCHC (g/dL) | RDW-SD (fL) | PLT (109/L) |
---|---|---|---|---|---|
9.4 | 8.9 | 86 | 30.1 | 64.3 | 740 |






How would you classify the patient?