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A Flow-Cytometric Method for Assessing Leukocyte Contamination in White-Cell-Depleted Blood Products

Background: In this paper we describe a rapid, easy and reliable method for counting low levels of leukocytes in white cell-depleted blood products (platelet concentrates (PC) and packed red cells (PRC)) using flow cytometry. Material and Methods: The leukocytes nuclei are labeled by propidium iodide. The principle of the method is to add a known number of fluorescent beads to the probe containing an unknown number of leukocytes. Then, by counting simultaneously the WBC and the beads it is possible to determine the concentration of the leukocytes. The method was compared with the Nageotte hemocytometer-based technique. The leukocyte concentration was determined for each sample by flow cytometry as well as by microscopic counting, and the results were compared using Student’s t paired test and the correlation coefficient. 20 samples of PC and 15 samples of PRC were analyzed. Results: Student’s t paired test showed that there were no significant differences between the results of the methods (p = 0.2022 for PC and 0.5830 for PRC), and the correlation was very strong (r = 0.95548 for PC, 0.9453 for PRC) and highly significant (p ≤ 0.0001). Conclusion: The flow-cytometric method is suited for the routine control of the leukocyte concentration in blood products with a low level of WBC.