Study population and setting
This cross-sectional study established and compared the test performance characteristics of the Wantai SARS-CoV-2 Total Ab ELISA, the Euroimmun Anti-SARS-CoV-2 IgG and IgA ELISAs, and six point-of-care (POC) lateral flow immunoassays for IgG/IgM antibodies to SARS-CoV-2. The analysis included 30 serum samples from Danish ICU patients with confirmed SARS-CoV-infection. For negative controls, archived sera were obtained from healthy blood donors (n=10), patients with other acute viral respiratory tract infections, including other coronaviruses (n=50), and sera from patients positive for other infections including dengue virus and Epstein Barr virus (n=22).
Summary of Main Findings
The Wantai total antibody ELISA had the most accurate test performance characteristics with 93% sensitivity (the proportion of samples that are truly positive that test positive) and 100% specificity (the proportion of samples that are truly negative that test negative). The Euroimmun IgA ELISA had better sensitivity (93%) than the Euroimmun IgG ELISA (67%); however both assays had poorer specificity (93% for IgA and 96% for IgG) than the Wantai total antibody ELISA. Of the three false-positive results by the Euroimmun IgG ELISA, one serum sample came from a patient with antibodies to human coronavirus HKU1, and two samples came from patients with adenovirus antibodies, providing potential evidence of cross-reactivity. The test performance characteristics of the POC tests varied, and were generally lower than that of the ELISAs. POC test results were often discordant with ELISA results.
The study compared the performance of multiple assays in well-characterized specimens with laboratory confirmed SARS-CoV-2 infections representing a range of time since symptom onset. There was a diverse set of historical negative controls to test assay specificity, including specimens from patients with other acute viral infections including other coronaviruses.
The study had a small sample size. The study also did not include specimens from mild or asymptomatic cases with SARS-CoV-19 infection, or specimens from cases of SARS-CoV-19 infection that were no longer PCR-positive. There was a lack of serial sampling within an individual to better assess the performance of each assay over time since symptom onset.
This is the most comprehensive serologic assay validation study as of the date of publication, highlighting a significant degree of variability in serologic assay test performance characteristics of both commercially available ELISAs as well as point of care tests.