Large-volume hemocytometer chamber for accurate counting of white cells (WBCs) in WBC-reduced platelets: validation and application for quality control of WBC-reduced platelets prepared by apheresis and filtration.

A detailed description is provided of a method using a large-volume (50 microL) hemocytometer to count very low numbers of white cells (WBCs) in platelet components. A method employing a Nageotte hemocytometer uses crystal violet stain and a standard microscope with a reading time of 5 to 10 minutes. The method is validated by using serial dilutions of known concentrations of WBCs in platelets and by correlation with a flow cytometric technique. The interobserver coefficient of variation was 11.9 percent for WBC concentrations > 2 per microL. Use of the method for the evaluation of 203 WBC-reduced platelet components prepared by apheresis or by filtration revealed that over 94 percent of components had WBC content < 5 x 10(6). This method could easily be applied in the routine quality control of WBC-reduced platelet components and in clinical studies employing these components.