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CSMLS MLT Exam study materials
CSMLS MLT Exam study resources

CSMLS MLT Exam: Hematology: CBC, Morphology and Coagulation

CSMLS MLT Exam · Work through your exam, one topic at a time.

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Hematology: CBC, Morphology and Coagulation

Hematology questions test your ability to move from a complete blood count to a mechanism. The exam expects confident use of red cell indices, reticulocyte production, film morphology, and coagulation mixing studies, plus recognition of spurious results caused by specimen problems.

Core rules

  • Indices are calculated, not measured: MCV (fL) = Hct (L/L) x 1000 / RBC (x10^12/L); MCH (pg) = Hb (g/L) / RBC (x10^12/L); MCHC (g/L) = Hb (g/L) / Hct (L/L). Reference MCV 80-100 fL, MCH 27-33 pg, MCHC 320-360 g/L.
  • Anaemia classification: microcytic (iron deficiency, thalassaemia, anaemia of chronic disease, sideroblastic), normocytic (acute blood loss, haemolysis, renal disease, marrow failure), macrocytic (B12/folate, alcohol, liver disease, hypothyroidism, myelodysplasia).
  • Corrected reticulocyte count = retic % x (patient Hct / normal Hct); the retic production index further divides by maturation factor (about 2 when Hct is 0.25).
  • Coagulation: PT/INR monitors warfarin (extrinsic, factor VII); aPTT monitors heparin (intrinsic). A 1:1 mixing study that corrects immediately indicates factor deficiency; failure to correct, or correction only after incubation, indicates an inhibitor such as a lupus anticoagulant or factor VIII antibody.

Worked example

Hb 80 g/L, Hct 0.24 L/L, RBC 3.0 x10^12/L. MCV = 0.24 x 1000 / 3.0 = 80 fL. MCH = 80 / 3.0 = 26.7 pg. MCHC = 80 / 0.24 = 333 g/L. Reasoning: all three indices sit within or at the lower edge of reference limits, so this is a normocytic normochromic anaemia, and the workup turns to reticulocyte count, renal function and haemolysis markers rather than iron studies.

Traps that cost marks

  • Cold agglutinins falsely raise MCV and can push MCHC above 360 g/L; warm the sample at 37 degrees C and re-run.
  • EDTA-induced platelet clumping gives a spuriously low platelet count; check the film for clumps and redraw in citrate (correct the count for dilution).
  • MCHC above 370 g/L almost always signals an artefact: haemolysis in vitro, lipaemia, or a clotted sample.
  • Rouleaux (high protein) versus true agglutination (cold antibody) must be distinguished on film and by saline replacement.
  • Myeloperoxidase, Sudan Black B and specific esterase identify myeloid lineage; TdT marks immature lymphoid cells.