An immunological lab test to detect antibodies which attack the red blood cells of its own body (called autoantibodies). The test is important to the diagnosis of certain blood disorders. The test first reacts red blood cells with serum from the test individual, then with antibodies to the autoantibodies. If the autoantibodies exist, they will bind to the red blood cells. When the antibodies to the autoantibodies are added, they will bind the autoantibodies (still attached to the red blood cells) and cause the red blood cells to clump together. Large clumps of red blood cells indicate that the autoantibodies exist; absence of the clumps indicates that they don't.