The direct antiglobulin test: A critical step in the evaluation of hemolysis

Abstract

The direct antiglobulin test (DAT) is a laboratory test that detects immunoglobulin and/or complement on the surface of red blood cells. The utility of the DAT is to sort hemolysis into an immune or nonimmune etiology. As with all tests, DAT results must be viewed in light of clinical and other laboratory data. This review highlights the most common clinical situations where the DAT can help classify causes of hemolysis, including autoimmune hemolytic anemia, transfusion-related hemolysis, hemolytic disease of the fetus/newborn, drug-induced hemolytic anemia, passenger lymphocyte syndrome, and DAT-negative hemolytic anemia. In addition, the pitfalls and limitations of the test are addressed. False reactions may occur with improper technique, including improper washing, centrifugation, and specimen agitation at the time of result interpretation. Patient factors, such as spontaneous red blood cell agglutination, may also contribute to false results. Am. J. Hematol. 87:707-709, 2012. V

Lyse or not to lyse: Clinical significance of red blood cell autoantibodies

“…Several explanations for these DAT positives without hemolysis have been suggested. Some may be due to technical problems such as a poor washing technique or over-centrifugation [13], but this is probably only a minority. Elevated total serum IgG levels also have been suggested to cause a positive DAT [3,14].…”

“…Finally, the negative results could in some cases be due to inappropriate handling of the samples such as e.g. poor washing technique or improper agitation [13]. It should be noted that DAT-negative AIHA in general is characterized with less severe hemolysis than DAT-positive AIHA [21].…”

Autoimmune Hemolytic Anemia:Focusing on Therapy According to Classification

“…At the next step, monospecific reagents are used to detect anti-C3d and IgG separately. The presence of only C3d may indicate IgM type antibody [15,16].…”

Autoimmune Hemolytic Anemia and Red Blood Cell Autoantibodies

“…The sensitivity of a positive DAT for RBC autoantibodies can depend on the reagents used as well as the technical expertise of the personnel performing the test. 4 Rare IgA RBC autoantibodies will not be detected by routine DAT testing.…”