Automated differential leucocyte counters: an evaluation of the Hemalog D and A comparison with the Hematrak. I. Principles of operation; reproducibility and accuracy on normal blood samples.

The precision and accuracy of the Hemalog D, which uses cytochemical identification of cells in suspension, and of the Hematrak, which uses image recognition of cells on a stained blood film, have been compared counting normal blood samples. The Hemalog D showed superior precision for all cell types, as would be expected since 10,000 cells are counted per sample; however, the precision for monocytes was worse than expected for the number of cells counted. The precision of the Hematrak was equivalent or superior to that of a manual count of the same number of cells but showed the poor precision inevitable when only 100 cells are counted. With respect to accuracy, both automated counters showed statistically significant differences from manual counts and from each other in counting neutrophils, lymphocytes and eosinophils, bu the differences were not sufficiently great to be of practical importance. The Hematrak counted monocytes accurately (though imprecisely) whereas the Hemalog D overestimated monocytes on average by 2.3%, or 40% of the mean monocyte percentage. This was consequent on the counting of esterase positive neutrophils as monocytes, and the difference from the manual count was sufficient to be of some practical importance. The Hemalog D counted basophils both accurately and precisely. The precision of manual and Hematrak basophil counts was poor; the accuracy of the Hematrak basophil count was dependent on the quality of the stain and that of the manual basophil count was dependent on the quality of the stain and the attentiveness of the technologist. For other cell types in blood samples from normal volunteers, the Hematrak was versatile and accuracy was not greatly affected by the use of May-Grünwald-Giemsa rather than Wright's stain, nor by the use of hand spread rather than machine spread films.