Assessment of commercial lateral flow immunoassays for rubella IgM detection in serum samples

Background Rubella is generally a mild exanthematous disease, but infection during early pregnancy can result in congenital rubella syndrome. Accurate and timely diagnosis is essential for surveillance and outbreak control. The use of enzyme immunoassays (EIA) for the detection of rubella-specific IgM antibodies, as recommended by WHO, is limited by infrastructure, trained staff, and transport requirements. Lateral flow immunoassay-based rapid diagnostic tests (RDTs) could aid decentralized testing, yet data on their performance are currently limited. Methods Nine commercially available rubella IgM RDTs were evaluated using a serum panel and two EIAs for comparison. The panel included serial dilutions of rubella IgM-positive controls and pooled IgM-positive sera, as well as rubella IgM-negative pooled sera, a strong IgG-positive sample, and a measles IgM-positive sample. Results Most RDTs showed substantially lower analytical sensitivity than EIAs, detecting IgM only at higher antibody concentrations. Two RDTs demonstrated an apparently higher sensitivity but reduced specificity. No interference from high rubella IgG levels was observed. Conclusion Overall, the rubella IgM RDTs included in this study displayed substantial limitations in sensitivity and/or specificity. While they may support rapid case identification in settings with limited laboratory capacity, results should be interpreted cautiously and confirmed by EIA, particularly in elimination settings.