Preparation of test cells for the antiglobulin test.

Erythrocytes may be coated with blood group antibodies with or without reacting complement or sometimes apparently with complement alone. This may occur in vivo in such conditions as autoimmune acquired haemolytic anaemia, haemolytic disease of the newborn, or after transfusions of incompatible blood. It may occur in vitro also by the deliberate sensitization of erythrocytes during laboratory serological investigations. Blood group antibodies may be of immunoglobulin types gammaM, gammaA, or gammaG; we have never seen gammaD antibodies. The presence of these antibodies on the erythrocyte surface, together with complement components or the presence of complement components alone, may be detected by the direct antiglobulin test where sensitization occurs in vivo or by the indirect antiglobulin test where there is sensitization in vitro.