False Positive Result of the Direct Antiglobulin Test (DAT): The Role of the Elevated Level of Immunoglobulin G

Direct antiglobulin test (DAT) is a test that shows antibodies bound to the surface antigens of erythrocytes. In this article, our aim was to investigate whether a correlation exists between a DAT positive test and serum immunoglobulin (Ig) levels. In our clinic, all DAT positive patients were retrospectively studied. Patients who had not received a blood transfusion within the last three months and who were evaluated for Ig levels were enrolled in the study (n = 15). Of these subjects, 15 showed a DAT positive result. Ten patients did not show any clinical or laboratory signs of hemolysis, while five patients exhibited signs and symptoms of autoimmune hemolytic anemia (AIHA). While all subjects showed a DAT positive test result (Ig G +/- C-3), four patients without AIHA, and three patients with AIHA showed a positive indirect antiglobulin test (IAT). In patients with a higher level of immunoglobulin G (IgG), the treatment of the concomitant disease resulted in normalization of the IgG level and led to a negative DAT test. The conditions that lead to an elevation of Ig should be reviewed in patients who displayed a DAT positive test without hemolysis and who had not previously received a blood transfusion.