[Leukocyte differential of the Coulter VCS. Evaluation and modalities of use in comparison with the Coulter STKR and manual count].

The Coulter VCS is a flow cytometer which performs, from a 100 microliter blood sample, a full five-part differential by assessing the volume (V), high frequency conductivity (C) and laser light scatter (S) on each white cell counted. The authors evaluated the Coulter VCS and compared its results with those of the Coulter STKR (three-part differential) and of the manual count. Reproducibility (ten replicate analyses on six different normal samples) was studied by the three methods and showed coefficients of variation closed to the manufacturer's specifications except for monocytes. The correlation coefficients obtained from 345 normal samples were the following: VCS/manual count: 0.97 for neutrophils, 0.70 for eosinophils, 0.97 for lymphocytes and 0.57 for monocytes; VCS/STKR: 0.99 for granulocytes, 0.99 for lymphocytes and 0.70 for monocytes. Comparisons of means displayed statistical differences for some cell categories but without clinical consequences. The flag analysis of 313 abnormal samples showed a false positive rate of 3.1 p. cent for the VCS and 1.8 p. cent for the STKR, the false negative rate was 2.1 p. cent for the VCS and 3.6 p. cent for the STKR. Starting from total blood count parameters, the authors propose guidelines for appropriate use of the different leucocyte differential methods.