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 fo r 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 iodi de. The principle of the method is to add a known number of fluorescent bea ds to the probe containing an unknown number of leukocytes. Then, by counti ng simultaneously the WBC and the beads it is possible to determine the con centration of the leukocytes. The method was compared with the Nageotte hem ocytometer-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 coe fficient. 20 samples of PC and 15 samples of PRC were analyzed. Results: St udent's t paired test showed that there were no significant differences bet ween 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 h ighly significant (p less than or equal to 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.