Highlights The sensitivity of commercial SARS CoV-2 IgG antibody tests was 64.4–93.2 %. Positivity rate was higher with sera obtained 4 weeks than 2−3 weeks after RNA testing. Antibody tests based on nucleoprotein and glycoprotein showed similar sensitivity. Nucleoprotein- and glycoprotein-based antibody tests reacted with different sera.
SARS CoV-2 antibody assays measure antibodies against the viral nucleoprotein (NP) or spike protein. The study examined if testing of antibodies against both antigens increases the diagnostic sensitivity. Sera (N=98) from infected individuals were tested with ELISAs based on the NP, receptor-binding domain (RBD), or both proteins. The AUROCs were 0.958 (NP), 0.991 (RBD), and 0.992 (NP/RBD). The RBD- and NP/RBD-based ELISAs showed better performance than the NP-based assay. Simultaneous testing for antibodies against NP and RBD increased the number of true and false positives. If maximum diagnostic sensitivity is required, the NP/RBD-based ELISA is preferable. Otherwise, the RBD-based ELISA is sufficient.
SARS-CoV-2-specific IgM antibodies wane during the first three months after infection and IgG antibody levels decline. This may limit the ability of antibody tests to identify previous SARS-CoV-2 infection at later time points. To examine if the diagnostic sensitivity of antibody tests falls off, we compared the sensitivity of two nucleoprotein-based antibody tests, the Roche Elecsis II Anti-SARS-CoV-2 and the Abbott SARS-CoV-2 IgG assay and three glycoprotein-based tests, the Abbott SARS-CoV-2 IgG II Quant, Siemens Atellica IM COV2T and Euroimmun SARS-CoV-2 assay with 53 sera obtained 6 months after SARS-CoV-2 infection. The sensitivity of the Roche, Abbott SARS-CoV-2 IgG II Quant and Siemens antibody assays was 94.3% (95% confidence interval (CI) 84.3-98.8 %), 98.1 % (95% CI: 89.9-100 %) and 100 % (95% CI: 93.3-100 %). The sensitivity of the N-based Abbott SARS-CoV-2 IgG and the glycoprotein-based Euroimmun ELISA was 45.3 % (95% CI: 31.6-59.6 %) and 83.3 % (95% CI: 70.2-91.9 %). The nucleoprotein-based Roche and the glycoprotein-based Abbott receptor binding domain (RBD) and Siemens tests were more sensitive than the N-based Abbott and the Euroimmun antibody tests (p=0.0001 to p=0.039). The N-based Abbott antibody test was less sensitive 6 months than 4-10 weeks after SARS-CoV-2 infection (p = 0.0001). The findings show that most SARS-CoV-2 antibody assays correctly identified previous infection 6 months after infection. The sensitivity of pan-Ig antibody tests was not reduced at 6 months when IgM antibodies have usually disappeared. However, one of the nucleoprotein-based antibody tests significantly lost diagnostic sensitivity over time.
SARS-CoV-2-specific IgM antibodies wane during the first three months after infection and IgG antibody levels decline. This may limit the ability of antibody tests to identify previous SARS CoV-2 infection at later time points. To examine if the sensitivity of antibody tests falls off, we compared the sensitivity of two nucleoprotein-based antibody tests, the Roche Elecsis II Anti-SARS-CoV-2 and the Abbott SARS-CoV-2 IgG assay and three glycoprotein-based tests, the Abbott SARS-CoV-2 IgG II Quant, Siemens Atellica IM COV2T and Euroimmun SARS-CoV-2 assay with 56 sera obtained 6-8 months after SARS-CoV-2 infection. The sensitivity of the Roche, Abbott SARS-CoV-2 IgG II Quant and Siemens antibody assays was 94.6 % (95% confidence interval (CI) 85.1-98.9 %), 98.2 % (95% CI: 90.4-99.9 %) and 100 % (95% CI: 93.6-100 %). The sensitivity of the N-based Abbott SARS-CoV-2 IgG and the glycoprotein-based Euroimmun ELISA was 48.2 % (95% CI: 34.7-62.0 %) and 83.9 % (95% CI: 71.7-92.4 %). The nucleoprotein-based Roche and the glycoprotein-based Abbott RBD and Siemens tests were more sensitive than the N-based Abbott and the Euroimmun antibody tests (p=0.0001 to p=0.039). The N-based Abbott antibody test was less sensitive 6-8 months than 4-10 weeks after SARS-CoV-2 infection (p = 0.0002). The findings show that most SARS CoV-2 antibody assays correctly identified previous infection 6-8 months after infection. The sensitivity of pan-Ig antibody tests was not reduced at 6-8 months when IgM antibodies have usually disappeared. However, one of the nucleoprotein-based antibody tests significantly lost sensitivity over time.
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