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.
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