A comparison of the Coulter STKS, Coulter S+IV, and manual analysis of white blood cell differential counts in a human immunodeficiency virus-infected population.

The white blood cell differential counts obtained by manual analysis and those obtained by automated analysis using Coulter STKS and Coulter S+IV cell counters (Coulter Electronics, Hialeah, FL) in a human immunodeficiency virus (HIV)-infected population were compared. Linear correlation analyses showed the STKS to be less accurate than the S+IV in determinations of the lymphocyte and granulocyte count. This finding was confirmed by difference analyses and by determining the number of measurements that fell outside of 95% confidence limits. Similar analyses were also done on patients not known to be HIV infected, and there was no disparity found between the STKS and S+IV in that group. In the HIV-infected population, the discrepancy between the manual and automated granulocyte counts performed on the STKS, but not on the S+IV, increased with increasing red blood cell mean corpuscular volume. Physicians caring for, and investigators performing studies on, HIV-infected patients should be aware of the potential for falsely low granulocyte numbers when using the differential from the STKS.