Clinical aspects of Rh immunization. Philip Levine Award Address.

Abstract

A single injection of Rh-positive erythrocytes is sufficient to induce a primary antibody response in about 70% of Rh-negative subjects. In the remaining 30%, so-called “non-responders,” Rh-positive erythrocytes, even after repeated injections, have a strictly normal survival. In Rh-negative responders, primary Rh sensitization can be completely prevented by the injection of approximately 25 µ g. anti-Rh per ml. Rh-positive erythrocytes; the extent to which the minimum effective dose, expressed in this way, varies with the absolute amount of cells injected has not been defined. When Rh-negative women are given 250 µ g. of anti-Rh following delivery of a first Rh-positive pregnancy, it might be expected that Rh sensitization, as judged by the appearance of anti-Rh within the following few months or during a succeeding Rh-positive pregnancy, would be observed only in those cases in which transplacental hemorrhage exceeded 10 ml., i.e. , in about 0.3%. In fact, the failure rate is about 1.5%. It is probable that sensitization to Rh during pregnancy accounts for most of the apparent failures of suppressive therapy given after delivery.