•Normal: 7.5 μm diameter. Roughly the size of the nucleus of a small lymphocyte.
•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 haemoglobin 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; abetali-po-proteinemia, 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
Parasites: characteristic intracytoplasmic inclusions; malaria, babesiosis.
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.
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, Chediak-Higashi anomaly.
- Auer rods: eosinophilic, rod like 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-Huet anomaly, pseudo–Pelger-Huet or acquired Pelger-Huet 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 μm in diameter,they may not be counted as platelets by electronic counters.