Differential leukocyte counts have a long tradition as diagnostic tools in Medicine. Basophils represent a morphologically distinct granulocyte population in human blood. They are a rich source of histamine, leukotrienes, IL-4 and IL-13 (1, 2), major mediators of allergic inflammation (1). Although basophils cannot be missed in stained blood smears, their low frequency leads to an insufficient precision of visual basophil counts (3). A method based on manual counts of cells stained with toluidine blue has been described many years ago, but this technique is too laborious for routine clinical use (4). Thus, little is known about basophil counts in normal and disease conditions. Automated leukocyte differentiation analyzes several thousands of leukocytes thereby enabling in principal accurate determinations of basophil numbers (5). However, because morphological leukocyte differentiation is used as gold standard in Clinical Hematology, the validation of basophil counts has not attracted sufficient interest (6).
Using defined basophil markers and exclusions of other leukocyte populations we describe two independent methods for measuring the basophil percentage by flowcytometry in whole blood. The results are compared with data from two hematology analyzers.