Demonstration by Flow Cytometry of the Numbers of Residual White Blood Cells and Platelets in Filtered Red Blood Cell Concentrates and Plasma Preparations

Background and objectives: New-generation polyester filters provide significant depletion of white blood cells (WBC) and platelets (PLT) in filtered red blood cell concentrates (FRCC) and in filtered plasma preparations (FP). The aim of this study was to elaborate a sensitive flow cytometric method for monitoring residual WBC and PLT in FRCC and FP. Materials and methods: We determined the number of WBC in 500 μl FRCC of FP using 50 μl of a combination of monoclonal antibodies (MAB) against CD45 (FITC labeled) and CD19 (PE labeled). After lysis of red blood cells, we mixed a specific number of reference beads with the remaining WBC. The number of residual WBC related to the acquisition volume was defined by the acquired reference beads. Using this method, the detection limit (DL) was 3 WBC/μl. Alternative methods used MAB against CD45 (FITC and PerCP labeled) and CD14 (PE labeled) or lymphocyte subsets such as CD3 (FITC labeled) and CD19, CD4, CD8, CD16 and CD56 (PE labeled) in combination with CD45 (PerCP labeled). The DL values were 10 WBC/μl for the CD45/CD14 staining and 0.1 WBC/μl for the determination of both CD3+ and CD19+ lymphocytes. For residual PLT in FRCC or FP, we used an FITC-conjugated MAB against CD41, with reference beads to determine the acquisition volume. PLT were demonstrated in a green-fluorescence (FL1) single histogram after gating in the forward light scatter × 90° light scatter signal dot plot. PLT counting was as described for WBC. The DL value was about 2 PLT/μl. Results: Filtration with Pall WBF-1 filters reduces WBC by 4 log and PLT by 3–4 log, resulting in cell counts which are below the critical limit for causing adverse transfusion reactions. Conclusions: Flow cytometry techniques provide a reproducible and objective tool for counting residual WBC and PLT in blood preparations compared with the Nageotte hemocytometer. Absolute numbers of leukocyte and lymphocyte subpopulations are obtainable.