Winter transport, agglutinated red cells, and a platelet count of 52
A 71-year-old woman presents to the emergency department in January with three days of fatigue. Blood is collected at 06:40 into a 4 mL K2 EDTA tube, carried through an unheated outdoor corridor at about −5 °C for 20 minutes, and analysed at 08:15. Results: RBC 2.02 ×10¹²/L, haemoglobin 12.8 g/dL, haematocrit 38.4%, MCV 190 fL, MCHC 33.3 g/dL, WBC 7.4 ×10⁹/L, platelets 52 ×10⁹/L with the analyser flag "platelet clumps". The film shows large grape-like clusters of red cells and several platelet clumps; no schistocytes. Yesterday's platelet count was 231 ×10⁹/L. The patient is on no anticoagulant and has no bleeding.
1. Which of these values are spurious and which is trustworthy? Show the arithmetic that exposes the problem.
Read the worked answer
Calculate the derived indices. MCH = 12.8 ÷ 2.02 = 63 pg. A true MCH of 63 pg is physiologically implausible; values above roughly 40 pg essentially do not occur. That mismatch says the red cell count is falsely low, not that the haemoglobin is falsely high.
Haemoglobin is measured spectrophotometrically after red cells are lysed, so it is the most robust parameter here and 12.8 g/dL is probably the real value. Cold agglutinins clump red cells; the analyser counts each clump as one large particle, so RBC falls and MCV rises, and the haematocrit computed from them is wrong. The blood also sat at −5 °C, which promotes the phenomenon.
The platelet count of 52 ×10⁹/L with a clump flag, clumps on the film, and a count of 231 yesterday is pseudothrombocytopenia from EDTA-dependent agglutination, not thrombocytopenia. Reporting 52 could lead to a platelet transfusion or delay surgery.
2. What must the laboratory assistant do before any result is released, and in what sequence?
Read the worked answer
Red cells. Warm the specimen to 37 °C for about 15 minutes, mix gently, and rerun; ideally run a prewarmed aliquot so the analyser does not cool it again. Expect the RBC to rise and the MCV to fall to a believable figure. Confirm with a microhaematocrit if the analyser result stays implausible. Compare the corrected Hct to the Hgb: they should now agree.
Platelets. Do not simply repeat the EDTA tube - it will clump again. Recollect in sodium citrate (correct the count by about 1.1 for the dilution) or lithium heparin, and ask for the film to be reviewed for a platelet estimate.
Do not release any value until the corrected numbers are in hand. Both problems can be fixed within the hour; the temptation is to report the haemoglobin and move on, but a half-reported CBC with a false platelet count still drives clinical decisions.
3. How should the final report read, and what comment is appropriate?
Read the worked answer
Report the corrected values with a comment naming the phenomenon and the method, for example:
"Red cell agglutination present on film; specimen warmed at 37 °C and re-analysed before reporting. Platelet count performed on a sodium citrate specimen because of EDTA-induced platelet clumping; result corrected for dilution. Platelet estimate on film is adequate."
Include the corrected platelet count and the film estimate, not the EDTA number. If the clinician needs a baseline, note that earlier EDTA counts may also be unreliable and that a citrate or heparin tube should be used for future monitoring. Keep the raw EDTA results in the record for audit but not on the cumulative report graph, where a false drop to 52 will be read as a real event. The comment also protects the laboratory if the patient is later investigated for a bleeding disorder.