A New Test (Blocking Test) for Rh Sensitization. ∗

Abstract

As was first shown by Wiener and Peters, 1 sensitization of Rh-negative individuals against the Rh factor can often be detected by in vitro tests for anti-Rh agglutinins in the individual's plasma. However, it was soon found 2 , 3 that there are many Rh-negative patients who are strongly sensitized to the Rh factor, as proved by the occurrence of an intragroup hemolytic transfusion reaction or a baby with erythroblastosis (hemolytic disease of the fetus and newborn), yet the plasma does not contain demonstrable anti-Rh agglutinins. The purpose of this paper is to describe a new in vitro test, the “blocking test,” with the aid of which Rh sensitization can be detected in many of these problem cases.

The first blocking experiments were tried in 1941, when retests of some of the stored post-transfusion sera from the patients described by Wiener and Peters the year before showed these sera to be no longer active. It occurred to the writer that the antibodies might still be present and capable of combining with the test cells but incapable of agglutinating the cells. When the mixture of test cells and apparently inactive serum was first allowed to combine and subsequently active (capable of agglutinating Rh+ cells in control experiments), anti-Rh serum was added, it was found that the test cells were not agglutinated, apparently because the action of the active agglutinin had been blocked. However, the results obtained were irregular, and therefore experiments on this “blocking test” for Rh antibodies, which is a counterpart of the inhibition test for haptens and group-specific substances, were temporarily abandoned. Recently, when more satisfactory anti-Rh testing sera became available, the experiments were resumed.