PA13.2-4 | Performing Common Haematological Tests: Hb, RBC/WBC, DLC — Summary & Reflection

REFLECT

Think about a scenario in your CP posting: you receive an automated CBC showing WBC 25,000, platelet 400,000, with a 'left shift? blast?' flag. The patient is a 60-year-old man admitted for fever of 3 days. Walk yourself through: (1) What pre-analytical checks do you do? (2) Do you report the result before smear review? (3) What cells are you specifically looking for on the smear? (4) If you find 15% blasts, what do you do next? Write your answers in your log before moving to the summary.

KEY TAKEAWAYS

Core procedural framework for PA13.4:

• Hb: Cyanmethemoglobin at 540 nm is the gold standard (CV <1%); Sahli's is field use only (CV 5–10%, inaccurate for HbF).
• RBC count (manual): Hayem's fluid 1:200 dilution → Neubauer chamber → count 5 small squares → multiply by 10,000 → cells/µL.
• WBC count (manual): Turk's fluid 1:20 dilution → 4 large corner squares → multiply by 50 → cells/µL. Automated: impedance + light scatter. Watch for NRBC inflation and platelet clump artefacts.
• DLC: Wedge smear → Leishman stain → battlements scan in monolayer body (never the tail) → 100-cell count → report % and absolute counts.
• QC: Daily 3-level controls, Levey-Jennings chart, delta checks on every patient result.
• Key traps: Clotted EDTA (low counts), storage artefact (high MCV), DLC at tail (false neutrophilia), EDTA pseudothrombocytopenia (platelet clumps → repeat in citrate).
• Smear review rule: Any flag, any clinical suspicion, any platelet/WBC outside normal range → smear before reporting. Normal automated result in a well patient with no flags = report directly.

After this module and your CP lab session, you should be able to pipette, count, calculate, stain, scan, and — critically — know when the number in front of you is wrong before it reaches a patient.