Quality monitoring of haemapheresis platelet concentrates: sampling in EDTA helps with the standardization and improves the consistency.

At the North London Blood Transfusion Centre, all haemapheresis platelet concentrates (PC) are tested in duplicate by a Technicon H-1 analyser to provide accurate information on the cell separator performance and on the cellular content of packs before issue. Repeated counting on fresh samples (within 4 h) reveals spontaneous aggregation (SA), which causes inconsistency in the estimated platelet yields and invalidates the cellular indices. Preliminary work showed that sampling into EDTA eliminated SA. Further studies on the effect of EDTA were undertaken as follows: (i) using the same PCS preparations (n = 7) stored conventionally and sampled daily in tubes with and without EDTA, and (ii) using fresh V50 and CS3000 PC to assess the difference on samples routinely collected in EDTA tubes for 2 months compared to those collected without EDTA in the previous 2 months. EDTA improved concordance of duplicate counts in fresh products. The increase in platelet yield in V50 and CS3000 preparations (12-22% respectively) was associated with a concomitant decrease (60-74%) in erythrocyte contamination. The variation in leucocyte count (3-5%) was less pronounced but the percentage differential was affected. There was also a systematic increase (8-11%) in mean platelet volume (MPV) due to EDTA. In PCS preparations the EDTA-induced variation in the cellular indices remained essentially in the same order (2-6%), while the MPV decreased progressively on storage. The difference in MPV can be used to assess the storage stability of various PC preparations. The implication of a double sampling technique (CPDA-1 and EDTA/CPDA-1) in the quality monitoring of haemapheresis procedures is substantial.