Chapter 61: Examination of Blood Smears and Bone Marrow

BLOOD SMEARS

ERYTHROCYTE (RBC) MORPHOLOGY

• Normal: 7.5 μm diameter. Roughly the size of the nucleus of a small lymphocyte.

• Reticulocytes (Wright’s stain): large, grayish-blue, admixed with pink (polychromasia).

• Anisocytosis: variation in RBC size; large cells imply delay in erythroid precursor DNA synthesis caused by folate or B₁₂ deficiency or drug effect; small cells imply a defect in hemoglobin synthesis caused by iron deficiency or abnormal hemoglobin genes. The automated red cell distribution width (RDW) is a measure of anisocytosis.

• Poikilocytosis: abnormal RBC shapes; the following are examples:

  1. Acanthocytes (spur cells): irregularly spiculated; abetalipoproteinemia, severe liver disease, rarely anorexia nervosa.

  2. Echinocytes (burr cells): regularly shaped, uniformly distributed spiny projections; uremia, RBC volume loss.

  3. Elliptocytes: elliptical; hereditary elliptocytosis.

  4. Schistocytes (schizocytes): fragmented cells of varying sizes and shapes; microangiopathic or macroangiopathic hemolytic anemia.

  5. Sickled cells: elongated, crescentic; sickle cell anemias.

  6. Spherocytes: small hyperchromic cells lacking normal central pallor; hereditary spherocytosis, extravascular hemolysis as in autoimmune hemolytic anemia, G6PD deficiency.

  7. Target cells: central and outer rim staining with intervening ring of pallor; liver disease, thalassemia, hemoglobin C, and sickle C diseases.

  8. Teardrop cells: myelofibrosis, other infiltrative processes of marrow (e.g., carcinoma).

  9. Rouleaux formation: alignment of RBCs in stacks; may be artifactual or due to paraproteinemia (e.g., multiple myeloma, macroglobulinemia).

RBC INCLUSIONS

• Howell-Jolly bodies: 1-μm-diameter basophilic cytoplasmic inclusion that represents a residual nuclear fragment, usually single; asplenic pts.

• Basophilic stippling: multiple, punctate basophilic cytoplasmic inclusions composed of precipitated mitochondria and ribosomes; lead poisoning, thalassemia, myelofibrosis.

• Pappenheimer (iron) bodies: iron-containing granules usually composed of mitochondria and ribosomes resemble basophilic stippling but also stain with Prussian blue; lead poisoning, other sideroblastic anemias.

• Heinz bodies: spherical inclusions of precipitated hemoglobin seen only with supravital stains, such as crystal violet; G6PD deficiency (after oxidant stress such as infection, certain drugs), unstable hemoglobin variants.

• Parasites: characteristic intracytoplasmic inclusions; malaria, babesiosis.

LEUKOCYTE INCLUSIONS AND NUCLEAR CONTOUR ABNORMALITIES

• Toxic granulations: dark cytoplasmic granules; bacterial infection.

• Döhle bodies: 1- to 2-μm blue, oval cytoplasmic inclusions; bacterial infection, Chédiak-Higashi anomaly.

• Auer rods: eosinophilic, rodlike cytoplasmic inclusions; acute myeloid leukemia (some cases).

• Hypersegmentation: neutrophil nuclei contain more than the usual 2–4 lobes; usually >5% have ≥5 lobes or a single cell with 7 lobes is adequate to make the diagnosis; folate or B₁₂ deficiency, drug effects.

• Hyposegmentation: neutrophil nuclei contain fewer lobes than normal, either one or two: Pelger-Hüet anomaly, pseudo–Pelger-Hüet or acquired Pelger-Hüet anomaly in acute leukemia.

PLATELET ABNORMALITIES

• Platelet clumping: an in vitro artifact—is often readily detectable on smear; can lead to falsely low platelet count by automated cell counters.

• Giant platelets: can be a sign of a very young platelet or increased platelet production or abnormal karyocyte maturation; if the platelets are >5–6 ...