Multicentric evaluation of two chemiluminescent immunoassays for IgG and IgM antibodies towards Rubella virus.

BACKGROUND: Screening and diagnosis of Rubella virus infection rely on testing for specific IgG and IgM. Immunoassays may yield different IgG results especially at low values, with difficulties in the evaluation of protective immunity. IgM levels decrease until negative a few weeks or months after acute infection, but individual and assay-related variability is common. OBJECTIVES: To evaluate the performance characteristics of the automated immunoassay for Rubella IgG and IgM on the Abbott ARCHITECT. STUDY DESIGN: Twelve laboratories from 7 different Italian regions assayed 6268 routine specimens, comparing qualitative results for IgG and IgM and quantitative for IgG with other widespread immunoassays. Prevalence data for IgG were disaggregated by patients' group and by age in order to evaluate vaccination coverage. RESULTS: Qualitative concordance for IgG was 97.3% vs. Abbott AxSYM, 95.0% vs. DiaSorin Liaison and 97.7% vs. Behring Enzygnost; ARCHITECT was more sensitive than Liaison and equivalent to the other assays, with a good correlation of IU/mL values with AxSYM (r=0.89). IgG prevalence was 87.1% among pregnant women, indicating a sub-optimal vaccine coverage. IgM reactivity was 1%, except in one site due to an outbreak. IgM concordance was 97.5% vs. Abbott AxSYM, 97.9% vs. DiaSorin Liaison and 97.7% vs. Behring Enzygnost; ARCHITECT was more specific than AxSYM. CONCLUSIONS: Our study confirms that in Italy Rubella vaccination coverage among pregnant women is insufficient. The new Rubella IgG and IgM assays on the ARCHITECT analyzer showed a good performance in comparison with other commercial methods. The results obtained and the good precision, indicate their suitability for routine testing