Direct Antiglobulin Test
Serologic test to detect red blood cells (RBCs) that are coated with complement and/or antibodies in-vivo (in the body). The test is also known as the “Direct Coombs” test or simply by the abbreviation “DAT.” The test tube version of the DAT is done by washing a patient sample of red cells to rid the sample of unbound antibody and complement, adding anti-human globulin (AHG), centrifuging briefly, and examining for agglutination. A positive DAT does not necessarily mean anything, as a large percentage of people with positive DAT’s have no problem at all. However, positive DATs are seen in adult patients with acute and delayed hemolytic transfusion reactions, autoantibodies (including those associated with warm and cold autoimmune hemolytic anemias), and certain drug-induced hemolytic events, to name a few. Babies with hemolytic disease of the newborn usually have positive DATs. A positive DAT can be evaluated further by many different methods, including elution and adsorption.
For more on the DAT, please listen to my friend Sue Johnson discuss it on the Blood Bank Guy Essentials Podcast, episode 028. Also, the DAT is often confused with the IAT; see my blog post on this confusion for more details.
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