Automatic volumetric capillary cytometry for counting white cells in white cell-reduced plateletpheresis components

BACKGROUND: As the benefits of white cell (WBC)‐reduced blood components become increasingly apparent, the need has arisen for a simple, automated WBC‐counting technique that is sensitive to low WBC concentrations. Automated volumetric capillary cytometry was evaluated for its ability to quantify residual WBCs in WBC‐reduced plateletpheresis components. STUDY DESIGN AND METHODS: The volumetric capillary cytometry system evaluated uses a laser to excite fluorescent dye‐labeled nucleated cells. The number of nucleated cells per μL is reported. Four studies were performed: linearity, precision of results near the value of 5 × 106 WBCs per unit, the limit of detection, and correlation to the Nageotte manual counting method. RESULTS: Assay values correlated to expected values (range, 0–125 WBC/μL) with an r2 > 0.99. In the range of 5 × 106 WBCs per unit the CV was 8.5 percent, and concentration differences of 0.15 log10 were detectable. The limit of detection was 1.0 WBCs per microliter (95% upper confidence limit). The assay correlated to the Nageotte method with an r2 of 0.98, slope of 1.0, and y‐intercept of 2.0 WBCs per μL. Assay results were 10 to 15 percent higher than Nageotte results, in samples with values near 5 × 106 WBCs per unit. Technician time per sample was 2 to 3 minutes. CONCLUSION: Volumetric capillary cytometry is precise and sensitive to small differences in WBC concentration in the range of clinical interest. The device provides an efficient new method for quality assurance and control of WBC‐reduced plateletpheresis products.