A delineation of performance criteria for the differentiation of leukocytes.

Performance criteria for manual differential leukocyte counting are tentatively set following analysis of the CAP interlaboratory survey programs in hematology. It is evident that intermediate levels of discrimination of five normal leukocyte types (neutrophils, eosinophils, basophils, lymphocytes, and monocytes) can be achieved by almost all laboratories. The most sophisticated level (differentiating band from segmented neutrophils and reactive from normal lymphocytes) is still somewhat controversial. Sampling and other variables when doing 100-cell differential counts at the intermediate level of discrimination are quite predictable, and CAP Survey results closely parallel the predicted results when uniform wedge of centrifuged smears stained in an acceptable manner are used. Automated differential counters should be expected to perform at a level of discrimination at least as good as that of human examiners.