Hematology: Indices, Anemia Classification, Morphology, and Flow Cytometry
The hematology section covers the CBC and derived indices, anemia classification, peripheral morphology, and the immunophenotype of hematologic neoplasms.
Indices and the reticulocyte response
MCV = Hct/RBC × 10; MCH = Hgb/RBC × 10; MCHC = Hgb/Hct × 100. The reticulocyte count must be corrected for anemia: corrected retic % = retic % × (patient Hct ÷ 45), and the reticulocyte production index divides further by a maturation factor (about 2 for Hct 25–35%). A high corrected retic indicates blood loss or hemolysis with an intact marrow; a low one points to production failure.
Anemia by MCV
Microcytic: iron deficiency (low ferritin, high TIBC, high RDW), thalassemia (normal or high ferritin, normal RDW, target cells, microcytosis out of proportion to anemia), anemia of chronic disease, sideroblastic anemia. Normocytic: blood loss, hemolysis, renal disease, aplastic anemia. Macrocytic: B12/folate deficiency, alcohol, liver disease, hypothyroidism, MDS, and reticulocytosis.
Morphology and flow cytometry
Schistocytes suggest microangiopathy; spherocytes suggest immune hemolysis or hereditary spherocytosis; rouleaux suggest a paraprotein; basophilic stippling suggests lead toxicity or thalassemia. Flow cytometry assigns lineage: CD34/CD117 immaturity, MPO myeloid, CD3 T cells, CD19/CD20 B cells, CD5 with CD23 in CLL, CD10 in follicular lymphoma and ALL, CD38/CD138 plasma cells.
Worked example
Hemoglobin 7.5 g/dL, hematocrit 22%, retic 12%. Corrected retic = 12 × (22/45) = 5.9%, a strong marrow response. With a normal MCV, elevated indirect bilirubin, and elevated LDH, the picture is hemolytic anemia; a DAT then separates immune from non-immune causes.
Traps that cost marks
Cold agglutinins falsely elevate MCV and MCHC - recheck at 37 °C. EDTA-induced platelet clumping causes pseudothrombocytopenia; examine the smear before reporting. Do not interpret indices from a lipemic or hemolyzed sample without a smear review.