External quality assurance for CD34 cell enumeration--results of a preliminary national trial. Royal Microscopical Society Clinical Flow Cytometry Group QA Schemes.

With the development of haematopoietic stem cell (HSC) mobilisation strategies and the associated technical expertise in leukapheresis has come the need for accurate and reproducible enumeration of HSC in the peripheral blood. Enumeration of HSC is not only required for timing of the harvest but is valuable in determining that the minimum number of HSC required for successful engraftment has been collected. In order to establish a minimum number of HSC required, results from multiple institutions performing such transplants need to be assessed. Clearly, to compare results from multiple centres requires confidence in the reproducibility of the assay. We have evaluated an established EQAS method which has already been proven in the external quality assurance of CD4 measurement in clinical samples to assess the inter- and intra-laboratory reproducibility of CD34 measurement. Fifteen laboratories participated in two distributions in which 28 samples were analysed. Standardised methods were not employed, laboratories using their routine methods. Participants reported their results in terms of '% positive of total leukocytes' and 'absolute number of CD34+/microliters'. A wide range of clinical samples was despatched and analysed with CD34 cell content ranging from 0.08-19.31% positive. The coefficients of variance (CV) associated with the estimations of relative proportions and absolute numbers were maximally 100.1 and 136.6%, respectively. This study highlights the need for external quality assurance and standardisation of the methodology of this assay.