Detection of rubella virus-specific IgM employing trypsin-treated human group O erythrocytes was evaluated using the method of sera fractionation on sucrose density gradients (SDG) and that of sera absorption with staphylococcal protein A. The former method proved to be highly specific and sensitive in confirming or excluding rubella by demonstration of specific IgM. In contrast, the latter method provided comparable results in only 71.43% of specimens tested by both methods while false-positive or -negative IgM results were obtained in the remaining 28.57% of specimens. In view of these results, therefore, it is recommended that all those specimens found positive for specific IgM by the protein A method must be confirmed by another procedure, possibly that of specific IgM reduction with 2-mercaptoethanol.
ABO Blood-Group System Antibodies, Viral