An evaluation of anti-rubella virus immunoglobulin G (IgG) immunoassays that report in international units per milliliter (IU/ml) was performed to determine their analytical performance and the degree of correlation of the test results. A total of 321 samples were characterized based on results from a hemagglutination inhibition assay. The 48 negative and 273 positive samples were used to determine the sensitivity and specificity of the assays. When equivocal results were interpreted as reactive, the sensitivity of the immunoassays ranged from 98.9 to 99.9% and the specificity ranged from 77.1 to 95.8%. All assays had positive and negative delta values of less than 2. A significant difference between the mean results of all assays was demonstrated by analysis of variance. However, post hoc analysis showed there was good correlation in the mean results expressed in IU/ml between some of the assays. Our results show the level of standardization between anti-rubella virus IgG immunoassays reporting results expressed as IU/ml has improved since a previous study in 1992, but further improvement is required.Rubella virus causes a relatively benign childhood rash and fever. However, primary maternal infection during the first trimester is associated with a 80 to 90% risk of congenital rubella syndrome (2,3,25). In developed countries, the risk of congenital rubella syndrome has been minimized through vaccination programs (22-24) and by testing pregnant women for evidence of rubella virus immunoglobulin G (IgG) at their first antenatal visit (10, 11). Since the isolation of rubella virus in 1962, rubella testing has developed continuously, with the hemagglutination inhibition (HAI) assay often being considered the reference method (4,15,29).Since the 1980s, rubella virus IgG assays have been calibrated against the same World Health Organization (WHO) international standard rubella virus serum (second standard preparation) and test results have been reported in international units per milliliter (IU/ml). The introduction of quantitative measurement of rubella virus IgG had the potential to increase standardization and facilitate the comparison between the results of different tests.In 1992, we published a multicenter evaluation comparing commercial immunoassays used to measure rubella virus IgG antibodies (9). The conclusion was that, although there was a moderate degree of correlation, reporting anti-rubella virus IgG levels in IU/ml had insufficient practical use. At that time, we concluded that the results of rubella virus antibody testing be confined to a statement concerning immunity rather than a numerical value. More than 15 years later, the assays compared in the 1992 study are no longer in common usage in Australia and have generally been replaced with random-access analyzers that perform a range of immunoassays of multiple disciplines. A comparison of six random-access and two microtiter plate (MTP) immunoassays that report anti-rubella virus IgG levels in IU/ml was undertaken to review analytical performance a...

Three automated assays (Abbott AxSYM, Bayer ADVIA Centaur, and bioMerieux VIDAS) used for the detection of rubella virus-specific immunoglobulin M were evaluated. A total of 57 samples from individuals with evidence of infection with rubella virus were used to estimate sensitivity, and 220 samples from blood donors and individuals attending an antenatal clinic who had no evidence of recent infection were used to estimate specificity. Seroconversion panels comprising an additional 31 samples from four individuals were used to determine clinical sensitivity. Samples containing potentially cross-reacting substances were also tested. The sensitivities of the three assays ranged from 84.2 to 96.5%, and the specificities ranged from 96.8 to 99.9%. The Abbott AxSYM assay detected more reactive samples than the other two assays when a panel of 57 positive samples was tested. Bayer ADVIA Centaur detected more reactive samples in the seroconversion panels than the other two assays. All three assays evaluated reported a reactive result in 1 or more of the 48 samples containing potentially cross-reacting analytes. The assays demonstrated comparable performance in testing of a well-characterized panel of samples.Infections with rubella virus (RV) are usually mild, often presenting with a maculopapular rash of the head and trunk, lymphadenopathy, a fleeting fever, and arthritis (11, 30). Studies have shown that 20 to 50% of infections are subclinical. However, serious sequelae result from maternal infection during the first trimester of pregnancy, with a 90% risk of fetal damage if the infection occurs in the first 2 months of pregnancy and a 50% risk if infection occurs in the third month (7,11,15). The teratogenic effects of infection in utero include ocular defects (cataracts, retinopathy, and glaucoma), partial or complete cochlear deafness, and mental retardation associated with microcephaly or encephalitis (7,15,30). The effects of congenital rubella syndrome are lifelong. In adulthood, affected individuals have been reported to have increased levels of diabetes, osteoporosis, and thyroid disorders (9).Typically infection occurs via the respiratory route, with viral replication occurring in the nasopharynx. The incubation period is 2 to 3 weeks, with viremia occurring during the second week. Symptoms are usually apparent at the time of the viremia and for several days after the rash appears. Rubella virus can be isolated from nasopharyngeal samples for as long as 2 weeks after the rash (6, 30). The antibody response also coincides with the viremia (30). RV-specific immunoglobulin M (RV IgM) is detectable after the incubation period, usually at the time of the maculopapular rash. RV IgM usually declines to undetectable levels after approximately 8 weeks. RV IgG levels rise more slowly, reach a peak several weeks after symptoms disappear, and persist for life (30). As the RV IgG response matures, the avidity of the antibody reaction to RV increases (25,26).Diagnosis of primary RV infection in adults can be difficult (1, 6...