Indirect Coombs test

a test routinely performed in cross-matching blood or in the investigation of a transfusion reaction, based on sensitisation of erythrocytes in vitro In the indirect Coombs test, a patient's serum (test serum) is incubated with a suspension of donor erythrocytes (or erythrocytes of known antigenic composition). If specific antibodies are present, they become attached to the antigen in the donor cells (sensitization of red cells). After a washing step with saline, Coombs antihuman globulin is added to cause agglutination of sensitized cells. Appearance of agglutination at this point indicates that the test serum had indeed antibodies specific for antigens on the surface of donor or panel erythrocytes.