1. Following large transfusions of low titer group O blood into patients of group A, B, and AB it was not possible to demonstrate foreign isohemolysins or incomplete antibodies in the serum of recipients. Cold isoagglutinins were frequently demonstrated immediately after the transfusion, but they usually disappeared rapidly. Its several patients the titer of foreign anti-A isoagglutinin was quite high and the antibody persisted in the circulation for several days. It was suggested that the persistence of these agglutinins may have been possible because there was a relatively small amount of A substance in the body of the recipient. Where the transfused isoagglutinins persisted the patients were found to be nonsecretors or weak secretors of A substance in the saliva.

2. In most of these patients there was evidence of a selective destruction of recipient red cells after the transfusion of O blood. This was probably due to the activity of transfused isoantibodies in the plasma of the O blood. This hemolytic activity was observed where it was not possible to demonstrate the presence of foreign isoantibodies. It is suggested that there may exist forms of antibody that cannot be demonstrated by laboratory methods. These antibodies manifest themselves only by causing destruction of red cells in vivo.

3. Clinically the hemolytic disease on the basis of such transfused isoantibodies while causing destruction of native red cells did not threaten the lives or impede the recovery of these patients. No reactions were encountered and none were heard of in Korea that might have been ascribed to a dangerous universal donor. The partition of group O blood into high titer and low titer on the basis of dilution of 1:200 to 1:256 has proved in practice to be safe.

4. The persistence of foreign antibodies after a large transfusion of group O blood may make it impossible to cross match the patient’s blood with blood of his hereditary group. Severe transfusion reactions have occurred when group specific blood has been given following large transfusions of group O blood. It has been recommended that after a large transfusion of group O blood has been given, group specific blood should not be used for at least two weeks.

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