True volumetric method for flow cytometric enumeration of CD34+ stem cells and its agreement with a standard bead-based single-platform protocol

Background aims. Stem cells are commonly enumerated with bead-based methods in blood and marrow progenitor cell transplantation centers. We compared the International Society of Hematotherapy and Graft Engineering (ISHAGE) bead-based method with a true volumetric one that obviates the use of fluorescent beads for enumeration. Methods. From 31 samples, including 15 peripheral blood samples and 16 leukapheresis products, CD34(+) cells were enumerated with the single-platform bead-based ISHAGE method and a true volumetric method. After exclusion of two outliers, one from the peripheral blood group and the other from the leukapheresis group, the results were compared. Results. In the peripheral blood category, no significant difference was observed. However, a proportional systematic error was seen in the leukapheresis group. The systematic error was corrected in the leukapheresis group using a regression line equation. The 95% confidence interval of differences was [-5.83, 2.18] for the peripheral blood and [-38.40, 38.77] for the leukapheresis group after correction of the systematic error. Conclusions. The true volumetric method is a simple and reliable approach that can be used instead of the more popular bead-based procedures.