Hematopathology
Hematopathology questions usually begin with a CBC and require reasoning from morphology, immunophenotype, and genetics simultaneously. Master the anemia algorithm: MCV plus reticulocyte count first, then iron studies (ferritin is an acute-phase reactant; soluble transferrin receptor helps when inflammation confounds), then hemoglobin analysis (elevated HbA2 supports beta-thalassemia trait, but iron deficiency can normalize it).
Know the defining lesions: JAK2 V617F, CALR, and MPL in myeloproliferative neoplasms, with BCR-ABL1 excluded for essential thrombocythemia and primary myelofibrosis; BCR-ABL1 for CML; recurrent translocations in AML, with PML-RARA demanding urgent ATRA. Separate CLL (CD5+, CD23+, dim surface immunoglobulin) from mantle cell lymphoma (CD5+, cyclin D1+, t(11;14)) and hairy cell leukemia (CD11c, CD25, CD103, BRAF V600E). Plasma cell myeloma requires SLiM-CRAB criteria, not merely increased plasma cells. In coagulation, a prolonged PTT that corrects with normal plasma suggests factor deficiency; failure to correct suggests an inhibitor.
Traps
- Calling a reactive lymphocytosis clonal without demonstrating light-chain restriction.
- Overdiagnosing myelodysplasia when B12 or copper deficiency explains the dysplasia.
- Mistaking schistocytes from a mechanical valve for TTP.
- Forgetting that DIC lowers fibrinogen while TTP typically leaves PT/INR normal.
Worked example. Platelets 25 × 10^9/L, schistocytes, LDH 900 U/L, undetectable haptoglobin, normal creatinine, normal PT/INR: this constellation suggests TTP. Send ADAMTS13 and start plasma exchange immediately rather than waiting for the result, because untreated mortality is high.