The Coombs test, also called direct antiglobulin test, is designed to detect immune-mediated erythrocyte destruction which occurs in autoimmune hemolytic anemias, and in some cases with infections and neoplastic disorders. Hemolysis in these diseases is caused by erythrocytes being coated with antibody (IgG, IgM) and/or complement components (C3). Coated erythrocytes are either lysed in the bloodstream and/or removed by phagocytes. The Coombs reagent is an antiserum to IgG, IgM, and C3 prepared in goats. After obtaining the antiserum from the goat, complement is inactivated by heat and then the antiserum is absorbed repeatedly with washed normal erythrocytes. These treatments ensure that the Coombs reagent will not react with normal erythrocytes. However, erythrocytes that are coated with IgG, IgM, and/or C3 will be agglutinated by the Coombs reagent that contains antibodies to IgG, IgM, and C3.
