Evaluation of two novel enzyme immunoassays using recombinant antigens to detect cytomegalovirus-specific immunoglobulin M in sera from pregnant women

Background: Two novel enzyme linked immunosorbent assays (ELISA) (Abbott IMx CMV IgM 2.0, and Cobas Core CMV IgM EIA recomb, research version) which use recombinant antigens to detect cytomegalovirus (CMV)-specific IgM antibodies were evaluated. Objectives: A new ELISA is normally evaluated against a gold standard commercial kit, which in this case does not exist. We therefore evaluated the two novel recombinant ELISA against four conventional ELISAs and a recently developed CMV IgM immunoblot containing four purified viral and four recombinant proteins. Study design: A total of 280 sera from pregnant women and 42 potentially cross-reactive sera were investigated using the six ELISAs, including 101 sera which were also tested using the new IgM immunoblot. Results: Relative sensitivity, relative specificity and overall agreement differed according to the reference assay. The Cobas Core CMV EIA recomb showed much higher agreement with the ELISA consensus, and the IMx CMV IgM 2.0 with the immunoblot. Conclusion: The evaluation of these new IgM assays in terms of their agreement with either commercial ELISA kits or the IgM immunoblot demonstrates that the question ‘which reference method?’ is still open. However the recombinant IgM assays may improve the diagnosis of CMV infection in pregnancy since the recombinant technology offers helpful tools for identifying diagnostically relevant proteins and allows the use of standardized pure preparations of antigens. For serological diagnosis of CMV infection in pregnancy two IgM assays that can be relied upon should be performed. IgM positive sera should be tested with supplementary assays to differentiate primary from non-primary infection.