Reducing costs in flow-cytometric counting of residual white blood cells in blood products: utilization of a single-platform bead-free flow-rate calibration method

BACKGROUND: Commercial flow‐cytometric methods for counting residual white blood cells (rWBCs) in leukoreduced blood products use calibration beads for estimation of the measured sample volume. A bead‐free flow‐rate calibration method is developed and validated. STUDY DESIGN AND METHODS: The analyzed volume was calculated by acquisition time (ACQ). Twenty‐nine spiking series of red blood cell (RBC) or platelet (PLT) products were prepared containing levels ranging from 0.08 × 106 up to 2048 × 106 WBCs/L. Nearly WBC‐free triple‐leukofiltered RBCs or PLT concentrates (PCs) served as background. Propidium iodide (PI) was used to identify rWBCs. Five RBC series were compared against a commercially available kit (LeukoSure, Beckman Coulter). Routine capabilities were tested on 41 RBC and 92 PC samples of two independent transfusion services. RESULTS: The lower detection limit in RBC was 0.08 × 106 rWBCs/L for ACQ and 0.16 for LeukoSure. Criteria for linearity, accuracy, and precision were fulfilled within the range of 0.5 × 106 to 512 × 106 WBCs/L. For PCs, all these criteria were fulfilled between 0.5 × 106 and 32 × 106 rWBCs/L (lower detection limit of 0.25) for PI. ACQ and LeukoSure agreed sufficiently (81%) when tested on routine RBCs or PCs. CONCLUSION: A residual WBC count of fewer than 0.5 × 106 WBCs/L can be accurately counted using the ACQ approach at a total reagent cost of less than 0.5€ per sample.