Quality control study by the French Cytometry Association on flow cytometric DNA content and S-phase fraction (S%). The Association Française de Cytométrie.

Clinical use of flow cytometric (FCM) DNA analysis requires effective quality controls. Thirty-two laboratories with various degrees of FCM experience participated in the first phase of a quality control program organized by the Association Française de Cytométrie. All received diskettes containing ten list-mode files and ten histogram files that were derived from FCM analysis of various unfixed tumor specimens. A total of 610 responses on DNA ploidy and cell cycle were obtained with three different DNA analysis softwares: CellFit used by (44% of responses), MultiCycle (44%), and ModFit (12%). After statistical analysis, 31% of the responses were excluded from the final analysis for precise reasons. The groups were too small to carry out a valid analysis of the slight differences in the percentage of cells in the DNA synthesis phase (S%) between CellFit and MultiCycle. To estimate the influence of gating on the final cell-cycle results, five of the histogram files were derived from corresponding list-mode files, but the participating laboratories were unaware of this. A good correlation (r = 0.98) was obtained for S% values in the five paired files. The fact that 31% of the responses had to be excluded clearly reflects inadequate training in the use of these analysis softwares and, in some cases, a failure to grasp the biological meaning of the results. In contrast, the laboratories fulfilling consensus recommendations obtained remarkably homogeneous results, showing that standardization is feasible.