VALIDATION OF USE OF THE NAGEOTTE HEMOCYTOMETER TO COUNT LOW-LEVELS OF WHITE CELLS IN WHITE CELL-REDUCED PLATELET COMPONENTS

Background: Determination of the white cell (WBC) count in WBC-reduced platelet components requires methods that have a detection limit in the range of approximately 5.0 x 10(2) to 5.0 x 10(4) per mL. Study Design and Methods: With a 50-mu L Nageotte hemocytometer and bright-field microscopy (200x magnification), studies were conducted to develop and validate a method that could be used routinely with filtered and apheresis-harvested platelets. A 1-in-5 dilution of sample with a commercially available blood-diluting fluid was used because, with a lower (1-in-2) dilution, the observed number of WBCs was substantially less than the number expected at relatively high platelet counts (>1.9 x 10(9)/mL). Results: The observed and expected WBC counts in WBC-reduced platelet samples correlated well at levels between approximately 5 and 1100 WBCs per counting area (5.0 x 10(2) - 1.1 X 10(5)/mL). At levels of more than 300 to 400 WBCs per counting area, accurate counts were obtained when 10 of the 40 rectangles were counted. Conclusion: These studies provide data to confirm that the 50-mu L Nageotte hemocytometer can be used to accurately count low levels of WBCs in platelet components.