Antiglobulin (Coombs') tests are used to detect nonagglutinating antibodies or complement molecules on red cell surfaces. They are used most commonly in immunohematology laboratories and blood banks for routine cross-matching, antibody screening tests, and preliminary investigations of hemolytic anemias.14,15
The tests are based on the principle that immunoglobulins (i.e., antibodies) act as antigens when injected into a nonhuman host. This principle was originally published by Moreschi in 1908, but his findings drew little notice. In 1945, Coombs' independently rediscovered the principle when he prepared antihuman serum by injecting human serum into rabbits. The rabbit antibody produced against the human globulin was then collected and purified. This antihuman globulin was used to demonstrate incomplete human antibodies that were adsorbed to red cells and did not cause visually apparent agglutination unless Coombs' rabbit serum was used. The two applications of the test currently used are (1) the direct antiglobulin test (direct Coombs') and (2) the indirect antiglobulin test (indirect Coombs').16