Effectiveness of prophylactic Rh immunosuppression after transfusion with D-positive blood

In a published investigation 42 D-negative men were transfused with single units of D-positive R1r (CDe/cde) blood to mimic the D-incompatible transfusion accidents occasionally seen in young D-negative women. Twenty-two men received no therapy and 20 were treated with Rh immunoglobulin in a calculated dose of 20 mug of anti-Rh per milliliter of infused red cells. The reported incidence of serologic D alloimmunization was 81.8 per cent in control and zero per cent in treated recipients. Posttransfusion 51Cr clearance studies with a challenge with the use of 5 ml. of D-positive cells from the same donor at five months in these identical subjects vary from the results based upon the presence of circulating anti-D active antibody. Exponential immune clearance curves occurred in two control and nine treated recipients. As the first evidence of D alloimmunization is an immune Cr clearance curve followed at some later time by circulating active anti-D antibodies, these data could suggest that Rh immunization actually was 90.9 per cent in untreated control subjects and 45 per cent in treated men. The dose of passive Rh immunoglobulin effective in prophylaxis of transfusion Rh immunization of a D-negative person is still not definitely established, but apparently it is greater than 20 mug of anti-Rh per milliliter of D-positive erythrocytes received.