Flow cytometric enumeration of CD34(+) hematopoietic stem and progenitor cells (HPC) is the reference point for undertaking apheresis and evaluation of adequacy for PBSC engraftment. An external quality assurance (EQA) scheme for CD34(+) HPC enumeration has been operational in Belgium, Netherlands and Luxemburg (Benelux) since 1995. Within this group, a multicenter survey was held to validate the state-of-the-art methodology, i.e., multiparametric definition of HPC based on light scatter, expression of CD34 and CD45, and counting beads (i.e., 'single platform ISHAGE' method).

Methods

'Real-time' EQA was used to monitor the application of the single-platform ISHAGE method by 36 participants. Three send-outs of stabilized blood with CD34(+) cell counts 35-60 cells/mL were distributed to 36 participants, who were required to assay the samples on three occasions using the standard assay and their local techniques. These results were compared with those obtained by 111-116 UK NEQAS participants testing the same specimens.

Results

Using the single platform ISHAGE method, between-laboratory coefficients of variation (CVs) as low as 10% were achieved. Intra-laboratory CVs were < 5% for &SIM; 50% of the participants. Local single-platform techniques yielded between-laboratory CVs as low as 9% in both Benelux and UK NEQAS cohorts. In contrast, the lowest between-laboratory CVs using dual-platform techniques were 17% (Benelux) and 21% (UK NEQAS), respectively.

Conclusion

The single-platform ISHAGE method for CD34(+) cell enumeration has been validated by an international group of 36 laboratories. The observed variation between laboratories allows a meaningful comparison of CD34(+) cell enumeration results.