Flow‐Cytometric Method for Counting Very Low Numbers of Leukocytes in Platelet Products1

Abstract
We provide a detailed description of a new method for counting very low numbers of leukocytes present in platelet products. The method uses fluorescent staining of leukocyte DNA using propidium iodide and flow cytometry. The assay is accurate over a range of leukocyte concentrations from 0.1 to 10 WBC/.mu.l. We validated the method using specially designed studies and applied it to the measurement of leukocyte content in leukocyte-depleted platelet products prepared by apheresis or filtration. This method should prove useful in studies which address the clinical impact of leukocyte-depleted platelet products.