Direct Antiglobulin Test (DAT)

The DAT is a serologic test to detect red blood cells (RBCs) that are coated with complement and/or antibodies in-vivo (in the body). Among physicians caring for patients at the bedside, this test is often referred to as the “Direct Coombs Test,” which makes we blood bank nerds nervous, but that’s ok!

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. A baby with hemolytic disease of the newborn will usually have a positive DAT. It’s very important to remember that the DAT is typically done in response to some event or clinical concern. Routine DATs on hospitalized patients are not recommended, as so many of them are unimportant (i.e., evaluation of the positive DAT does not lead to a significant clinical issue). The “evaluation” I just mentioned might include procedures like elution or adsorption, to name a few.

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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