Comparative evaluation of three flow cytometers for reticulocyte enumeration

Flow cytometric determination of reticulocytosis is progressively replacing the manual microscopic method. We evaluated three flow cytometers (Becton Dickinson FACScan, Coulter EPICS Profile II, Ortho Cytoron Absolute) for reticulocyte enumeration, using thiazole orange. For each sample, 30,000 cells were analysed. In order to comparatively evaluate the three instruments, reticulocytes were counted by manually gating the erythroid population and evaluating the gated population for fluorescence characteristics. The different instruments showed good linearity and precision. No carry-over was observed. Orthogonal regression analysis of reticulocyte counts of 100 healthy blood donor samples and 108 haematological patient samples showed a good mutual comparability between all three instruments tested, although the paired t-test showed a significant difference between the Cytoron and both the FACScan and the Profile. Despite minor statistical differences, the three instruments can be considered equivalent for daily routine reticulocyte enumeration.