QUALITY ASSESSMENT OF CD34(-CELL ENUMERATION - EXPERIENCE OF THE INGDOM-NATIONAL-EXTERNAL-QUALITY-ASSESSMENT-SCHEME (UK NEQAS) USING A UNIQUE STABLE WHOLE-BLOOD PREPARATION() STEM)

CD34(+) peripheral blood stern cell (PBSC) mobilization and harvesting has rapidly replaced autologous bone marrow as a source of stem cells for transplantation. Timing and adequacy of harvests rely upon the ac curate enumeration of circulating CD34+ cells, However, previous EQA p rogrammes have reported interlaboratory CVs as high as 284%, suggestin g the need for greater standardization. In addition the routine use of fresh and/or frozen cells as analytes also introduces antigen instabi lity as a variable factor, To circumvent this problem and achieve a tr ue reflection of interlaboratory variation, we have used a novel whole blood preparation in which the antigenic profiles of PBSCs, as determ ined by flow cytometry, are retained for > 200 d. This international s cheme, currently the largest in the world, distributes aliquots of sta bilized whole blood bi-monthly to 91 laboratories in 20 countries (44 U.K., 47 overseas). Participants are required to determine the percent age and absolute values for CD34+ PBSCs using in house techniques. Ado pting such a preparation, a more accurate determination of interlabora tory variation has been possible when compared to previous EQA studies , with CVs as low as 22% and 24% for percentage and absolute counts. I n addition the programme has established that a wide range of methods are in routine use, emphasizing the urgent requirement for national/in ternational consensus guidelines.