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A Coombs test (also known as Coombs' test, antiglobulin test or AGT) is either of two clinical blood tests used in immunohematology and immunology. The two Coombs tests are the direct Coombs test (DCT, also known as direct antiglobulin test or DAT), and the indirect Coombs test (also known as indirect antiglobulin test or IAT).

The direct Coombs test is used to test for autoimmune hemolytic anemia; i.e., a condition of a low count of red blood cells (aka RBCs) caused by immune system lysis or breaking of RBC membranes causing RBC destruction.

In certain diseases or conditions, an individual's blood may contain IgG antibodies that can specifically bind to antigens on the RBC surface membrane, and their circulating RBCs can become coated with IgG alloantibodies and/or IgG autoantibodies. Complement proteins may subsequently bind to the bound antibodies and cause RBC destruction.[1] The direct Coombs test is used to detect these antibodies or complement proteins that are bound to the surface of red blood cells; a blood sample is taken and the RBCs are washed (removing the patient's own plasma) and then incubated with antihuman globulin (also known as "Coombs reagent"). If this produces agglutination of RBCs, the direct Coombs test is positive, a visual indication that antibodies (and/or complement proteins) are bound to the surface of red blood cells.

The indirect Coombs test is used in prenatal testing of pregnant women and in testing blood prior to a blood transfusion. It detects antibodies against RBCs that are present unbound in the patient's serum. In this case, serum is extracted from the blood sample taken from the patient. Then, the serum is incubated with RBCs of known antigenicity; that is, RBCs with known reference values from other patient blood samples. If agglutination occurs, the indirect Coombs test is positive.[2]

The two Coombs tests are based on the fact that antihuman antibodies, which are produced by immunizing nonhuman species with human serum, will bind to human antibodies, commonly IgG or IgM. Animal antihuman antibodies will also bind to human antibodies that may be fixed onto antigens on the surface of red blood cells (also referred to as RBCs), and in the appropriate test tube conditions this can lead to agglutination of RBCs. The phenomenon of agglutination of RBCs is important here, because the resulting clumping of RBCs can be visualised; when clumping is seen the test is positive and when clumping is not seen the test is negative.

Common clinical uses of the Coombs test include the preparation of blood for transfusion in crossmatching, screening for atypical antibodies in the blood plasma of pregnant women as part of antenatal care, and detection of antibodies for the diagnosis of immunemediated haemolytic anemias.

Examples of alloimmune hemolysis[edit]
Hemolytic disease of the newborn (also known as HDN or erythroblastosis fetalis)
Rh D hemolytic disease of the newborn (also known as Rh disease)
ABO hemolytic disease of the newborn (the indirect Coombs test may only be weakly positive)
AntiKell hemolytic disease of the newborn
Rh c hemolytic disease of the newborn
Rh E hemolytic disease of the newborn
wikipidea
https://en.wikipedia.org/wiki/Coombs_...

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