Hematology and Blood Transfusion Science
Hematology and blood transfusion science covers the complete blood count, anaemia classification, haemostasis testing and safe transfusion. The exam favours interpretation: which red cell indices point to which cause, which coagulation test explores which pathway, and which step prevents a haemolytic transfusion reaction.
Core rules
- Classify anaemia by MCV: microcytic (<80 fL), normocytic (80–100 fL), macrocytic (>100 fL). Always add the reticulocyte count to separate hypoproliferative from regenerative anaemia.
- Iron deficiency: low ferritin, high TIBC, low saturation, high RDW. Thalassaemia trait: high HbA2 on electrophoresis with a normal ferritin.
- PT and INR test the extrinsic and common pathway; APTT tests the intrinsic and common pathway. A mixing study that corrects indicates factor deficiency; failure to correct suggests an inhibitor such as lupus anticoagulant.
- Transfusion: group and screen, then crossmatch. Group O negative red cells are the emergency universal choice.
Worked example
A 28-year-old woman has Hb 8.4 g/dL, MCV 68 fL, RDW 17%, ferritin 6 ng/mL and a raised TIBC. The microcytic anaemia with depleted iron stores is iron deficiency, most likely from menstrual loss. Heavier-than-expected periods, gastrointestinal loss and pregnancy should be excluded before simply prescribing iron. If ferritin were normal or high and HbA2 raised, thalassaemia trait would be the better answer.
Traps
Diagnosing thrombocytopenia from an EDTA sample with platelet clumping (request a citrated tube and blood film); ignoring cold agglutinins that falsely raise MCV and MCHC; and transfusing without a documented pre-transfusion sample and bedside identity check.