Hematopathology: Blood, Marrow, Nodes and Coagulation
Hematopathology tests anemia classification, leukemias, lymphomas, plasma-cell neoplasms and coagulation. The exam emphasizes peripheral smear, marrow morphology, immunophenotype and molecular findings.
Core rules
- Microcytic anemia: iron deficiency, thalassemia, anemia of chronic disease and sideroblastic anemia. Ferritin is usually low in iron deficiency and normal or high in inflammation.
- Macrocytic anemia: B12/folate deficiency, liver disease, alcohol, hypothyroidism and myelodysplasia.
- Acute leukemia has blasts; chronic leukemia has mature-appearing cells. Flow cytometry defines lineage and clonality.
- Lymphoma diagnosis requires architecture, morphology and immunophenotype; Hodgkin lymphoma has Reed-Sternberg cells in an inflammatory background.
- Multiple myeloma requires clonal plasma cells plus CRAB features or a myeloma-defining event.
- Coagulation tests: PT measures extrinsic/common pathway; APTT measures intrinsic/common pathway; mixing studies help detect inhibitors.
Worked example
A 52-year-old man has fatigue, splenomegaly and WBC 85,000/uL with left shift, basophilia and thrombocytosis. Marrow shows hypercellularity with myeloid hyperplasia. FISH detects t(9;22) BCR-ABL1. This is chronic myeloid leukemia, chronic phase. Reasoning: leukoerythroblastic features and basophilia suggest a myeloproliferative neoplasm, and BCR-ABL1 confirms CML. A leukemoid reaction lacks BCR-ABL1 and basophilia.
Traps
Do not diagnose iron deficiency from low MCV alone. Thalassemia trait often has high RBC count and normal ferritin. APL is associated with DIC, not just bleeding. CLL is CD5-positive; mantle cell lymphoma is CD5-positive but cyclin D1-positive. Smoldering myeloma has no CRAB features.