![]() ![]() In the appropriate test tube conditions, this can lead to agglutination of RBCs and allowing for visualisation of the resulting clumps of RBCs. Additionally, these anti-human antibodies will also bind to human antibodies that may be fixed onto antigens on the surface of red blood cells (RBCs). These anti-human antibodies are produced by plasma cells of non-human animals after immunizing them with human plasma. The two Coombs tests are based on anti-human antibodies binding to human antibodies, commonly IgG or IgM. Schematic showing the direct and indirect Coombs tests If agglutination occurs, the indirect Coombs test is positive. The serum is incubated with foreign red blood cells of known antigenicity. In this case, serum is extracted from a blood sample taken from the patient. The test detects antibodies against foreign red blood cells. The indirect Coombs test is used in prenatal testing of pregnant women and in testing prior to a blood transfusion. If the red cells then agglutinate, the direct Coombs test is positive, a visual indication that antibodies or complement proteins are bound to the surface of red blood cells and may be causing destruction of those cells. To perform the test, a blood sample is taken and the red blood cells are washed (removing the patient's own plasma and unbound antibodies from the red blood cells) and then incubated with anti-human globulin ("Coombs reagent"). The direct Coombs test is used to detect antibodies or complement proteins attached to the surface of red blood cells. The direct Coombs test is used to test for autoimmune hemolytic anemia-that is, a condition where the immune system breaks down red blood cells, leading to anemia. These antibodies could act against certain red blood cells and the test can be done to diagnose reactions to a blood transfusion. The indirect Coombs detects antibodies that are floating freely in the blood. Since these antibodies sometimes destroy red blood cells, a person can be anemic and this test can help clarify the condition. ![]() The direct Coombs test detects antibodies that are stuck to the surface of the red blood cells. They are the direct and indirect Coombs tests. ![]() Blood test used in immunohematology Coombs testĪ Coombs test, also known as antiglobulin test ( AGT), is either of two blood tests used in immunohematology. ![]()
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