Evaluation of Eight Anti-Rubella Virus Immunoglobulin G Immunoassays That Report Results in International Units per Milliliter

Abstract

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...

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