Background: WBC counting, an essential part of quality monitoring of WBC-reduced blood components, is carried out logistically within 48-72 h of collection. The between-laboratory variability and effects of 24-48 h storage were investigated using three major counting technologies.
Study design and methods: Samples of RBC and platelets with WBC in the range 0-50/microl were transported by courier. WBC counting was performed on days 1 and 2, by IMAGN 2000, flow cytometry and Nageotte, initially using local protocols and then using a national flow protocol. Up to 15 laboratories participated in each exercise.
Results: For "real failed leucodepleted" red cell products, higher levels of variability were observed for flow and Nageotte, as compared to IMAGN. For spiked RBC samples at critical decision making point (3-20 WBC/microl), between-laboratory the coefficients of variation (CVs) were low for IMAGN and were the highest for Nageotte. Flow cytometry CVs were generally high but improved subsequent to standardisation of sampling and the gating strategy. A similar pattern in the variability of results was observed for platelet concentrates. Sign tests using all samples (carried out for each method in each exercise; 25 in total) demonstrated no overall tendency for larger WBC counts to be recorded on day 1 when compared to day 2, although this difference was significant (p < 0.001) in certain cases depending on the nature of the spiked product.
Conclusions: We conclude that while a good performance is achieved using validated automated technologies for low residual leucocyte counting, the unification of reagents and standardisation of sampling and gating strategies are essential in obtaining interchangeable results. Unfixed RBC and platelet samples can generally be stored for 48 h before WBC counting.