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.