Rubella immunity: comparison of hemagglutination inhibition and radioimmunoassay antibody methods.

A threshold (1:10) rubella antibody hemagglutination inhibition (HAI) titer was obtained for 288 of 6537 (4.4%) obstetric patients. Random sera from 84 of these patients were compared for rubella antibody by both HAI and a very sensitive radioimmunoassay (RIA) technique. By RIA, 17% of the sera had no detectable rubella antibody, suggesting that those patients were truly susceptible to rubella. In addition, 8 of 55 paired prevaccine and postvaccine sera with titer increases demonstrated by HAI were analyzed by RIA. Seven of the 8 prevaccine sera were shown to have no rubella virus antibody by RIA, and RIA showed seroconversion in all 8 postvaccine sera.