Definition of "Coombs test"

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Coombs test (aka antiglobulin test, AGT) are 2 blood tests used in immunohematology.

Patient information

Coombs test, has that got anything to do with honeycombs ;P?
Not really . Another name for it is the antiglobulin test.

Antiglobulin? What is this?
Antiglobulin is an antibody against gamma globulin, which includes your antibodies (which are also called immunoglobulins).

Types
  • Indirect Coombs test (aka indirect antiglobulin test, IAT), is used in prenatal testing of a woman, and in testing blood prior to transfusion. It detects antibodies against RBC's present UNBOUNDED in the Pt's serum. Serum is extracted from the Pt, and incubated with RBC's of known antigenicity. If agglutination occurs, the indirect Coombs test is positive, indicating the presence of RBC antibodies
  • Direct Coombs test (aka direct antiglobulin test, DAT), used to test for autoimmune hemolytic anemia (i.e. low RBC, due to hemolysis). In autoimmune hemolytic disease, the Pt's circulating RBC's may be COATED with IgG autoantibodies, marking them for destruction by complement proteins. DAT is used to detect these antibodies bound to the RBC's. A blood sample is taken and the RBC's are washed, removing the Pt's own plasma. It is then incubated with Coombs reagant. If this produces agglutination of RBC's, the test is positive, indicating the IgG autoantibodies are bound to the RBC's surface

Patient information

There are different types of tests for antibodies against your body's antibodies?
Yep, so there's direct and indirect. So both test for antibodies against RBC's. Indirect tests this by looking for free flowing antibodies against RBC's. Direct tests it by searching for antibodies stuck to the surface of RBC's. The difference is that with the indirect test, your body actually KNOWS that it is foreign, so if you want to check for an AUTOIMMUNE problem (i.e. body attacking itself), you want to use the direct Coombs test.

See also

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Definition of Coombs test | Autoprac


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