Evaluation of automated basophil counting by using fluorescence-labelled monoclonal antibodies

The shortcomings of current methods of basophil enumeration detract from the clinical value of the basophil count. Moreover, sophisticated and costly techniques of automated basophil counting hardly can be validated for lack of a suitable reference method. We investigated whether a flow cytometric technique using double staining with fluorescence-labelled monoclonal antibodies (mAb) CD45-FITC and CD14-PE on a Coulter Epics Profile II could be used to evaluate basophil counting performance of hematology analyzers. The technique was compared with the 800-cell manual differential, the Coulter STKS, and the Cobas Argos 5 Diff. Precision: STKS, Argos and Profile II showed a precision analogous to a 2,173, 2,250-, and 14,705-cell differential, respectively, illustrating the superiority of automated methods. Accuracy (150 normal and abnormal samples): Using the Profile II as reference the STKS showed a notably weaker correlation than the Argos (r = 0.581 and 0.718, respectively), although this difference was nearly concealed when the imprecise manual differential served as reference (r = 0.517 and 0.562, respectively). The Profile II correlated relatively well with the manual differential (r = 0.730). Analyzing 137 healthy adult subjects, we obtained a reference range of 0.33 to 1.35% (0.020 to 0.102 x 10⁹ basophils/L) for the mAb-based method. These data would recommend mAb-based basophil counting as a valuable tool for instrument evaluation. However, an observed bias of 0.09% against the manual differential suggests that modifications are necessary before this technique can be considered as new reference method.