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Coombs Test, Indirect

The indirect Coombs reaction (indirect Coombs) is used to detect abnormal circulating antibodies in the patient's serum, which may react against the transfused red blood cells. These antibodies are different from those directed against blood groups A, B, and O. The indirect Coombs reaction is also different from the direct Coombs reaction, which detects antibodies that are already attached to the red blood cells.

In this test, the patient's serum is considered the source of the antibodies and the donor red blood cells are the cells-antigens. The serum and the red blood cells are brought together to allow any antibodies to attach to the red blood cells and then anti-human globulin is added. If the patient's serum contains antibodies that react and bind to the donor red blood cells, adhesion will occur and the test is considered positive. If no adhesion occurs then no antigen-antibody reaction has occurred. The serum may contain antibodies, but the donor red blood cells do not have the antigen to which the antibodies will react.

Possible Interpretations of Pathological Values
  • Positive indirect Coombs reaction: Erythroblastosis fetalis, hemolytic anemia (drug-induced), incompatible transfusion, Rh incompatibility during pregnancy, post-transfusion reaction.
  • Medications that may cause a positive indirect Coombs reaction: cephalosporins, chlorpromazine, insulin, isoniazid, levodopa, mefenamic acid, methyldopa, penicillin, phenytoin, procainamide, sulphinamides, tetracyclines.


Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.

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