Definition: Either of two tests for detecting red blood cell antibodies: the direct test, for detecting sensitized red blood cells in erythroblastosis fetalis and in acquired hemolytic anemia; and the indirect test, for cross-matching blood or investigating transfusion reactions. Also called antiglobulin test.

Explanation: The Coombs Test (also Coombs' Test) is a blood test used to determine whether there are red blood cell antibodies, which leads usually to hemolysis, especially in Rh disease. Coombs antibody is an anti-human globulin. It was first described in 1945 by Cambridge immunologists Robin Coombs, Arthur Mourant and Rob Race. The test is also used in screening blood prior to blood transfusion.

Two types of the test exist:

* Indirect Coombs test - also known as the indirect antiglobulin test (IAT). This is used in the matching of blood products. It detects immunoproteins present on red blood cell membranes, by adding a polyspecific antiserum which contains antibodies specific for human immunoglobulins and complement to agglutinate the cells.
* Direct Coombs test - also known as the direct antiglobulin test (DAT). It detects antibodies capable of attaching to normal red blood cells, by incubating normal red blood cells in the serum, washing the cells, and then using a polyspecific antiserum which contains antibodies specific for human immunoglobulins and complement to agglutinate the cells. The DAT is used to determine if the patient has immune-mediated hemolysis (antibody-mediated destruction of red blood cells), as occurs in Rh disease.

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