Quality assurance by a commercial flow cytometry method of leucodepletion of whole blood donations: initial application of universal testing and proposals for a batch-release sampling plan

We have used the Becton-Dickinson LeucoCOUNT test to monitor residual leuco cytes in whole blood by flow cytometry following leucodepletion filtration. This test was found to be quick, robust and reliable, and allowed measurem ent of residual leucocytes down to 2.25 x 10(4) leucocytes per unit, which was found to match approximately the limit of filter proficiency. The resul ts of testing > 1000 units showed a lognormal distribution with means betwe en log(10) 4.864 (0.73 x 10(5)) and log(10) 5.016 (1.04 x 10(5)) leucocytes per unit in the three different homogeneous groups of filtered units studi ed. The numbers of units with residual leucocytes exceeding the 5 x 10(6) u pper threshold were 1/577, 2/457 and 0/87 in these groups. The filtration p rocesses were validated according to the published BEST working party guide lines and were well within the 99% confidence and 95% tolerance target for the 5 x 10(6) upper threshold set for the UK. A sampling plan based on Brit ish Standard BS 6001 with elimination of outliers by the extreme studentize d deviate (Grubbs' test) was evaluated on random samples from these groups and has been adopted locally as a prospective batch-release criterion for r elease of leucodepleted blood.