Hematology
CBC and analyzers
Modern analyzers combine impedance and optical scatter, producing flags that require manual smear review. Nucleated RBCs inflate the WBC, so apply the correction: corrected WBC = WBC x 100 / (100 + nRBC per 100 WBC).
Anemia work-up
MCV classifies the anemia as microcytic, normocytic, or macrocytic. Iron deficiency shows low ferritin, high TIBC, and low saturation; anemia of chronic disease shows low iron, low TIBC, and normal-to-high ferritin. Correct the reticulocyte percentage for anemia: corrected retic % = retic % x (patient Hct / 45).
Coagulation
PT/INR monitors warfarin, aPTT monitors unfractionated heparin. A mixing study that corrects indicates factor deficiency; failure to correct indicates an inhibitor (including lupus anticoagulant or a specific factor antibody). INR = (patient PT / mean normal PT)^ISI.
Traps
- Platelet clumps or giant platelets cause a falsely low count; EDTA pseudothrombocytopenia resolves in a citrated tube.
- Cold agglutinins falsely raise MCV and MCHC; warm the sample.
- Lipemia falsely raises hemoglobin unless a plasma blank is used.
- MCHC above 36 g/dL suggests spherocytes, cold agglutinin, lipemia, or Heinz bodies.
- Automated flags never replace smear review for blasts or schistocytes.
- Classic translocations: t(9;22) BCR-ABL in CML, t(15;17) PML-RARA in APL, t(8;14) in Burkitt, t(14;18) in follicular lymphoma.
Rule of thumb
Two of three RBC indices moving in opposite directions (high MCV with high MCHC) almost always means interference, not true red cell pathology.