Detection of red blood cell-bound immunoglobulin G by flow cytometry and its application in the diagnosis of autoimmune hemolytic anemia.

Detection of autoantibodies to erythrocytes is of fundamental importance in the diagnosis of autoimmune hemolytic anemia (AIHA). The routinely used direct antiglobulin test (DAT) has the disadvantage of low sensitivity. In this study, we investigated the optimal test conditions of measurement of red blood cell (RBC)-bound immunoglobulin (Ig) G by flow cytometry (FCM). We studied 64 patients with AIHA, 30 anemic patients diagnosed with other diseases, and 36 healthy individuals. In 33 AIHA patients who were found to have RBC-bound IgG, both the mean fluorescence intensity (MFI) and percentage of fluorescence-activated RBCs were remarkably increased and results of both were considered positive. In the remaining 31 AIHA patients who had positive results for RBC-bound complement C3d, the MFI and the percentage of fluorescence-activated RBCs was also increased and 17 patients (54.8%) were considered to have a positive result by this method. In anemic patients with negative DATs the results of FCM were always negative. These results could be confirmed by enzyme-linked immunosorbent assay (ELISA), and the values obtained by FCM and ELISA corresponded to titration scores of the DAT. Additionally, in 3 of the other 8 patients who were suspected to have DAT-negative AIHA, RBC-bound IgG was detected by FCM and ELISA. Our investigation demonstrates that FCM is a precise, reliable, and sensitive method of detecting RBC-bound autoantibodies and could be used as a new routine diagnostic technique for AIHA and other immune hemolytic anemias.