Comparison of six commercially available SARS-CoV-2 antibody assays – choice of assay depends on intended use

Nilsson, Anna Christine; Holm, Dorte Kinggaard; Justesen, Ulrik Stenz; Gorm-Jensen, Thøger; Andersen, Nanna Skaarup; Øvrehus, Anne; Johansen, Isik Somuncu; Michelsen, Jens; Sprogøe, Ulrik; Lillevang, Søren Thue

Objectives Evaluate six commercial serological assays for detection of IgA, IgM or IgG SARS-CoV-2 antibodies in different disease severities. Methods Three lateral flow tests (LFTs) (Acro IgM/IgG, CTK IgM/IgG, Livzon IgM/IgG) and three ELISA assays (Euroimmun IgA and IgG, Wantai IgM) were included. Application was evaluated in samples from 57 SARS-CoV-2 RT-PCR positive patients stratified according to disease severity. Specificity was assessed using historical samples from 200 blood donors. Results While IgM LFTs failed to detect SARS-CoV-2 antibodies in 37–84% of non-hospitalised cases, the Wantai IgM ELISA detected antibodies in 79%. The Euroimmun IgG ELISA detected antibodies in 95% of non-hospitalised subjects. IgA, IgM and IgG ELISA levels were initially low, increased over time and correlated with disease severity. LFT sensitivity declined in samples taken >28 days after symptom onset/resolution. The Livzon IgG LFT had the highest specificity (98.5%), followed by the Euroimmun IgG ELISA (96.2%). The specificity for Euroimmun IgA ELISA improved (≥97.5%) using a custom cut-off value (4.0). Conclusions The sensitive and semi-quantitative ELISA assays are most appropriate for serologic detection of SARS-CoV-2 infection in mild cases. Livzon LFT and Euroimmun ELISA had the highest specificity among the IgG assays, making them most suitable for seroprevalence studies.