Red Blood Cell Inclusions

Introduction

• Red blood cell (RBC) inclusions include:
  • Those visible by Wright-Giemsa staining:
    • Nucleated RBC
    • Howell–Jolly bodies (nuclear fragments)
    • Pappenheimer bodies (iron-containing autophagosomes)
    • Cabot rings (mitotic spindle remnants)
    • Basophilic stippling (aggregates of ribosomes)
    • Hb C crystals
    • Parasites
  • Those visible by other stains:
    • Iron stains:
      • Siderosomes (iron-containing inclusions)
      • Confirmation of Pappenheimer bodies 
    • Intravital stains:
      • Heinz bodies (denatured globin)
      • HbH inclusions
  • Most RBC inclusions are found in young RBCs (reticulocytes).
  • The inclusions represent nuclear or cytoplasmic remnants.
  • They must be distinguished from:
    • Stain precipitate
    • Bubbles
    • Dirt on slide
    • Overlying platelets

Nucleated red blood cells

• Represents the presence of normoblasts in the peripheral blood, typically at orthochromatophilic stage of maturation. 
• Typically enumerated and reported as number of nucleated red blood cells (nRBCs) per 100 white blood cells. 
• Not necessary to distinguish the exact stage of maturation in the peripheral blood. The term nRBC encompasses all normoblasts circulating in the peripheral blood, regardless of maturation stage.
• Compared with a lymphocyte, the nRBC has:
  • Pinkish cytoplasmic color
  • Lower N:C ratio
  • Dark purple chromatic color
  • Coarse condensation of chromatin (pyknotic)
• Physiologically present at birth, generally disappear within 3-5 days.
• May be seen in:
  • Bone marrow replacement processes including:
    • Metastatic tumor
    • Marrow infiltration with leukemia/lymphoma
    • Marrow fibrosis
    • Marrow granulomas
  • Rapid RBC production, for example hemolytic anemias

Howell-Jolly Bodies

• Spherical, dark purple with Wright’s stain, vary widely in size and usually eccentrically located in the cell.
• Compared with Pappenheimer body:
  • Larger
  • Rounder 
  • Do not form tight clusters in pairs or tetrads
• Nuclear remnants or the result of abnormal mitosis in which a single chromosome fails to participate in the interphase nucleus and becomes detached:
  • The likelihood of the latter happening increases if the nucleus contains > 4N number of chromosomes prior to cell division as occurs in megaloblastic anemia. 
• Normally the spleen removes any Howell-Jolly body, hence their presence in the setting of asplenia. 
• Seen in:
  • Hyposplenism
  • Asplenism
  • Severe hemolytic anemia
  • Megaloblastic anemia

Basophilic Stippling

• Consists of multiple, uniform, evenly distributed fine or coarse dark dots (granules) scattered within the cytoplasm of RBCs.
• Two types of basophilic stippling:
  • Course:
    • RBC has variably sized (up to large) basophilic ‘granular’ discolorations across its entire cytoplasm on a Wright-stained film.
    • Never a normal finding; suggests impaired hemoglobin synthesis.
    • Seen in:
      • Thalassemia
      • Lead poisoning
      • Myelodysplastic syndrome
      • Sideroblastic anemia 
      • Congenital dyserythropoietic anemia
  • Fine:
    • RBC has small, uniform, punctate basophilic dots across its entire cytoplasm, on a Wright-stained film.
    • Associated with reticulocytosis; usually found in red cells that are larger and more polychromatophilic (purple) compared with neighboring non-stippled RBCs.
    • Of no clinical consequence.
• Stippled cells are created when reticulocytes from patients with incomplete RNA degeneration (or abnormal ribosomes) are dried slowly or stained supravitally with new methylene blue:
  • The RNA-containing ribosomes of reticulocytes aggregate during these processes and thus become visible as stippling.
  • In lead poisoning and thalassemia, the altered reticulocyte ribosomes have a greater propensity to aggregate, forming larger granules (coarse stippling). 

Pappenheimer bodies

• Pappenheimer bodies, or siderotic granules, appear in Wright-stained preparations as small, irregular basophilic (purple) coccoid granules < 1 um in diameter, sometimes clustered, and generally located near the cell periphery.
• Compared with basophilic stippling, Pappenheimer bodies occupy only one portion or region of the RBC.
• Compared with Howell-Jolly bodies, Pappenheimer bodies are:
  • Smaller
  • Less round, more angular
  • Form tight clusters in pairs or tetrads
• Wright Giemsa stains the protein matrix of the granules, while Prussian blue stains the nonheme iron component.
• Cells containing Pappenheimer bodies are termed siderocytes.
• Created when autophagosomes in RBCs digest abnormal iron-containing mitochondria.
• The autophagosomes are normally discharged from the cytoplasm or removed by the pitting action of the spleen.
• Seen in anemias which have in common a defect of incorporation of iron into the hemoglobin molecule.
• Observed in:
  • Asplenia
  • Megaloblastic anemia
  • Thalassemia
  • Hemolytic anemia
  • Sideroblastic anemia
  • Congenital dyserythropoietic anemia

Cabot Rings

• Appear as thread-like red or purple loops which may be single, double, or twisted as a figure-of-eight:
• Seen in:
  • Megaloblastic anemia
  • Severe anemia
  • Leukemia
  • Lead poisoning
  • Other causes of dyserythropoiesis

References

• JAMA. 1966;198(2):151-156

• Int J Hematol. 2013 Jun;35(3):351-7