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-microL 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-microL Nageotte hemocytometer can be used to accurately count low levels of WBCs in platelet components.