VARIABILITY IN ABSOLUTE LYMPHOCYTE COUNTS OBTAINED BY AUTOMATED CELL COUNTERS

There is increasing interest in the absolute lymphocyte count. This is partly driven by the need to obtain absolute values for lymphocyte su bsets such as absolute CD4(+) counts in human immunodeficiency virus ( HIV)-infected persons. The absolute total lymphocyte count is usually determined in the routine hematology laboratory on a separate sample f rom the same patient specimen and then combined with percentage result s from flow cytometry to obtain the absolute value of the lymphocyte s ubsets. We have studied analytic variability in the absolute lymphocyt e determination and compared it to the variability of the total white blood count (WBC). In a series of 524 specimens, four different automa ted methods were compared to each other and to the traditional eye cou nt differential, The automated methods were four widely used automated cell counters (Technicon H1, TOA NE8000, Coulter STKS, and Abbott CD 3000). The results indicate that analytic variability in the absolute lymphocyte counts, due, primarily, to method variability, is significa nt and is larger than the variability typically observed on interlabor atory trials of relative CD4 counts. These method biases cannot easily be reduced by calibration, since the cell classification algorithms a re built-in features of the various cell counters. Analytic variabilit y of the absolute lymphocyte counts was found to be 12.4% compared wit h analytic variability of only 4.9% for total WBC counts on the same s amples. Our data suggest that more precise results would be obtained i f flow cytometry results expressed each phenotype as a fraction of the leukocytes as well as total lymphocytes, Conversion to absolute value s could then be accomplished through determination of the total WBC in the routine hematology laboratory. (C) 1995 Wiley-Liss, Inc.