Prevention of Rh Immunization

Summary Four-hundred-and-fifty µgm of Rh0(D) antibody given I.M. 24 hours before transfusion of 2 ml of Rh-positive into Rh-negative ABO compatible recipient, causes rapid removal of the transfused cells. Fifty percent of the injected RBCs disappeared from the circulation with a mean T-V2 of 8 minutes (range 4-12 min). N o circulating donor RBCs were detected in the peripheral blood 4 hours after transfusion. The destruction of trapped 51Cr-labelled cells occurs over a three-day period primarily in the liver and spleen, presumably in the reticuloendothelial cells. Once trapped in the reticuloendothelial system, intact cells do not re-enter the circulation. Chromium-51 liberated after destruction of RBCs enters the plasma and is rapidly eliminated in the urine. No untoward reaction either local or systemic occurred after intramuscular injection of Rh0(D) antibody. Clinical trials to determine the minimum effective dose of antibody for routine and "high risk" group are needed but it is likely to be well below the dose of 450 µgm used in this study.