A rapid and reliable flow cytometric routine method for counting leucocytes in leucocyte-depleted platelet concentrates

Background and Objectives To ensure a proper quality control it is important to use a reliable method to count low numbers of leucocytes in leucocyte-reduced platelet concentrates (PCs). Materials and Methods A modified flow cytometric method for counting low numbers of leucocytes, based on a reference population contained in tubes with an exact number of fluorescent beads and staining with propidium iodide was used. To increase the number of events, the original sample volume was increased. Results There was a good correlation in the number of leucocytes (r = 0.99) between the modified flow cytometric method and microscopy of samples from unfiltered and expected numbers from serially diluted PCs. Samples from leucocyte-reduced PCs obtained by apheresis or filtered buffy coats showed no correlation between results from the modified flow cytometric method and microscopy (Nageotte). Conclusion Counting by microscopy gave a lower number of leucocytes than the modified flow cytometric method when counting a low number of cells. However, analysis of the serially diluted PCs proved that the modified flow cytometric method was reliable and rapid, making it suitable for clinical routine use.