Abstract The Coombs' test, also known as the antiglobulin test, is used most frequently in veterinary medicine as an aid in the diagnosis of immune-mediated hemolytic anemia. The test also is used widely in human medicine to screen for red blood cell alloantibodies. Polyspecific reagents for veterinary use typically contain anti-IgG, anti-IgM, and anti-C3. Monospecific reagents also are available. False-positive and false-negative test results can be obtained. Inadequate sensitivity of the standard test in human and veterinary medicine has necessitated development of alternate, more sensitive technologies.