Validation of the Nordic flow cytometry standard for CD34+ cell enumeration in blood and autografts: report from the third workshop. Nordic Stem Cell Laboratory Group.

Following two workshops on standardization of enumeration of CD34+ cells in blood and leukapheresis products, the Nordic Stem Cell Laboratory Group (NSCL-G) evaluated the Milan/Mulhouse/Nordic standard in clinical practice during the third workshop (WS-III). This report documents an acceptable interlaboratory variation in the most clinically active laboratories, with a coefficient of variation (CV) below 0.19 in 7 of 8 analyses performed. The introduction of a pan-CD45 antibody in the analysis did not improve the CV. Comparison of two different CD34 class II antibodies on a total of 99 samples and procedures with and without washing on a total of 96 samples revealed a significant correlation (r2 >0.99) for all analyses. Finally, subset analysis of uncommitted and lineage-specific progenitors revealed major gating difficulties, indicating that further improvements are necessary. In an analysis of more than 600 patients undergoing mobilization and harvest of blood progenitors, with about 500 patients autografted, we found a significant correlation between blood levels of CD34+ cells and recovery of CD34+ cells from each harvest as well as between CD34+ cell number reinfused and time to neutrophil and platelet recovery. This report documents for the first time that the very simple Milan/Mulhouse method (termed The Nordic Standard) can be used by a group of laboratories to obtain important clinical information. Consequently, we consider this method as the conventional method in quality assessment of autografts, which should provide a benchmark for development of second-generation improvements.