Quality assurance of CFU-GM assays: inter-laboratory variation despite standard reagents.

To investigate the hypothesis that commercial kits for CFU-GM (colony forming unit granulocyte-macrophage) assay will reduce the interlaboratory variation noted by many workers, we carried out a quality assurance exercise in 2 parts. There were 8 participants in the first study and each performed CFU-GM assays using their in-house method and a commercial kit (Stem Cell CFU Kit, Gibco) in parallel. In the second exercise there were 10 participants and each performed CFU-GM with in-house methods and with a different commercial medium (Methocult GF H4534, Stem Cell Technologies). Twelve samples of cryopreserved peripheral blood progenitor cells (PBPC) were analysed by each participant in each part of the study. A very wide range of results was found for the different in-house methods, but standardizing the clonogenic assay with the commercial kits did not reduce the variation seen. To improve the reproducibility of CFU-GM assays between laboratories, scrupulous attention should be paid to all the steps involved in the assays, as little progress will be made by using commercial medium in isolation from efforts to reduce other sources of variation.

Quality assurance of CD34+ cell estimation in leucapheresis products.

In order to examine the feasibility of an external quality assurance (QA) scheme for CD34+ cell enumeration and to identify causes of the differences between laboratories for CD34 counts, we carried out a pilot QA exercise in two parts. There were eight participating laboratories in the initial study and each performed CD34 counts using their in-house method. A series of 12 samples of cryopreserved peripheral blood progenitor cells (PBPC) were analysed by each of the eight laboratories. A very wide range of values for all the samples was found for the different in-house methods. For the second part of the study, 12 laboratories analysed a different set of 12 PBPC samples and each used the same anti-CD34 antibody (HPCA-2 PE), anti-CD45 antibodies to identify leucocytes, and counted a minimum of 50,000 events. These measures have reduced the interlaboratory variation in results but this variation is still too high to allow us to realistically compare values between centres. Overall, most centres performed comparably, but there was one centre in part one of the study which gave results that were significantly different from the other centres.