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.