Solid phase anti-IgM ELISA for detection of rubella specific IgM antibodies

IgM in the test sample was bound to anti-IgM on a solid phase consisting of a polystyrene microtest plate and rubella specific IgM antibody subsequently detected by incubation with crude rubella virus antigen and anti-rubella conjugate. High levels of rubella specific IgG, which decreased the sensitivity of an indirect ELISA for rubella IgM, did not interfere in the anti-IgM ELISA, whereas non-rubella IgM interfered by a competition for the anti-IgM on the solid phase. False-positive results owing to IgM rheumatoid factor could be prevented by the addition of aggregated IgG 0.1 mg/ml to the serum diluent. The median duration of the antibody response detected by the solid phase anti-IgM assay was 60 days (range 24-140) in test of serial serum samples from 17 patients with rubella. The assay appears suitable for routine diagnosis of postnatal rubella and will probably be particularly valuable for diagnosis of prenatal rubella.