MANUAL AND AUTOMATED METHODS FOR THE DETERMINATION OF LEUKOCYTE COUNTS AT EXTREME LOW-LEVELS - COMPARATIVE-EVALUATION OF THE NAGEOTTE CHAMBER AND THE ABBOTT CELL DYN-3500 ANALYZER

Leukodepleted or leukocyte-poor blood products (fresh-frozen plasma, p acked red cell and platelet concentrates in particular) are widely use d in current clinical practice. However, because the monitoring of leu kodepletion efficiency is generally carried out (if at all) using the labour-intensive and relatively inaccurate manual Nageotte chamber tec hnique, it is clear that any increased demand for leukodepletion monit oring would be difficult, if not impossible, to meet. As the need to i dentify an automated alternative to the Nageotte technique is importan t, this study was undertaken to evaluate such a possibility. White blo od cells were enumerated in a representative series of filtered and no n-filtered human blood components by both microscopic counting in the Nageotte chamber, and with the Abbott CD3500 automated haematology ana lyser. For the Nageotte estimate, a single analysis was made in accord ance with standard procedures, whereas the automated analysis was achi eved by making six replicate counts and determining the mean of four r eplicates after excluding the highest and lowest estimates. To determi ne linearity limits of the manual and automated procedures, freshly is olated leukocytes were admired with cell-free plasmapheresis plasma. R easonable reproducibility (mean CV 10% for cell counts exceeding 100 c ells/mu L) and good linearity (r>0.9) were observed for CD3500 determi nations in four separate experiments. The manual and automated measure ments also correlated well (r>0.9) with no obvious inter-method bias f or cell counts up to 40 cells/mu L although there was some suggestion of lower absolute CD3500 counts in the range 40-130 cells/mu L. For th e comparative studies with filtered and non-filtered blood products, n o significant method bias was seen with 70 individual red cell concent rates, but systematically higher CD3500 white blood cell counts were o bserved in the series of 68 platelet concentrates (probably due to the presence of platelet clumps). This study concludes that automation of white cell counts in blood products with the CD3500 analyser is feasi ble for quality control in the preparation of fresh-frozen plasma and red cell concentrates but is limited for the analysis of filtered plat elet concentrates. (C) 1997 Elsevier Science Ltd.