Reactivity of nonsensitized control erythrocytes in rubella passive hemagglutination assays

Two commercially available, nonsensitized control erythrocytes for use in rubella antibody passive hemagglutination assays detected nonspecific reactions in 10 of 600 (1.7%) and 9 of 500 (1.8%) sera tested. Reactive sera were positive with one or the other cell type, but not both. The probability of obtaining a false-positive result owing to a nonspecific passive hemagglutination reaction was estimated to be 0.17% for either cell type.