Diagnostic performance of seven rapid IgG/IgM antibody tests and the Euroimmun IgA/IgG ELISA in COVID-19 patients

OBJECTIVES: To evaluate the diagnostic performance of seven rapid IgG/IgM tests and the Euroimmun IgA/IgG ELISA for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in COVID-19 patients. METHODS: Specificity was evaluated in 103 samples collected before January 2020. Sensitivity and time to seropositivity was evaluated in 167 samples from 94 patients with COVID-19 confirmed with RT-PCR on nasopharyngeal swab. RESULTS: Specificity (confidence interval) of lateral flow assays (LFAs) was ≥91.3% (84.0–95.5) for IgM, ≥90.3% (82.9–94.8) for IgG, and ≥85.4% (77.2–91.1) for the combination IgM OR IgG. Specificity of the ELISA was 96.1% (90.1–98.8) for IgG and only 73.8% (64.5–81.4) for IgA. Sensitivity 14–25 days after the onset of symptoms was between ≥92.1% (78.5–98.0) and 100% (95.7–100) for IgG LFA compared to 89.5% (75.3–96.4) for IgG ELISA. Positivity of IgM OR IgG for LFA resulted in a decrease in specificity compared to IgG alone without a gain in diagnostic performance, except for VivaDiag. The results for IgM varied significantly between the LFAs with an average overall agreement of only 70% compared to 89% for IgG. The average dynamic trend to seropositivity for IgM was not shorter than for IgG. At the time of hospital admission the sensitivity of LFA was <60%. CONCLUSIONS: Sensitivity for the detection of IgG antibodies 14–25 days after the onset of symptoms was ≥92.1% for all seven LFAs compared to 89.5% for the IgG ELISA. The results for IgM varied significantly, and including IgM antibodies in addition to IgG for the interpretation of LFAs did not improve the diagnostic performance.