The direct Coombs' (antiglobulin) reaction is used to detect the presence of immunoglobulin or complement on the red-cell membrane and to determine the specific class of immunoglobulin or complement present.
Technique
For this test, red cells are washed to remove nonspecific adherent globulins. Rabbit antiserum to human gamma globulin and complement are then added to the washed cells. The rabbit antibody causes agglutination results when antibody or complement is bound to the red cell. Specific antisera to IgG or complement can be used to determine which of these substances is present on the red cell. The antibody can also be eluted from the patient's red cells and used to determine the antigenic specificity of the immunoglobulin.