Analytical evaluation and critical appraisal of early commercial SARS-CoV-2 immunoassays for routine use in a diagnostic laboratory.

Cramer, A.; Goodman, N.; Cross, T.; Gant, V. A.; Dziadzio, M.

BACKGROUND The objective of this study was to evaluate the performance characteristics of early commercial SARS-CoV-2 antibody assays in mild and asymptomatic subjects to enable the selection of suitable serological assays for routine diagnostic use within HCA Healthcare UK. METHODS We used serum samples from a pre-Covid era patient cohort (n=50, pre-December 2019), designated SARS-CoV-2 negative, and serum samples from a SARS-CoV-2 RT-PCR-positive cohort (n=90) taken > 14 days post symptom onset (April-May 2020). We evaluated 6 ELISA assays including one confirmation assay to investigate antibody specificity. We also evaluated one point-of-care lateral flow device and one high throughput electrochemiluminescence immunoassay. RESULTS The ELISA specificities ranged from 84-100%, with sensitivities ranging from 75.3-90.0%. The LFIA showed 100% specificity and 80% sensitivity using smaller sample numbers. The Roche CLIA immunoassay showed 100% specificity and 90.7% sensitivity. When used in conjunction, the Euroimmun nucleocapsid (NC) and spike-1 (S1) IgG ELISA assays had a sensitivity of 95.6%. The confirmation IgG assay showed 92.6% of samples tested contained both NC and S1 antibodies, 32.7% had NC, S1 and S2 and 0% had either S1 or S2 only. CONCLUSIONS These first generation assays were not calibrated against reference material and the results are reported qualitatively. The Roche assay and the Euroimmun NC and S1 assays had the best sensitivity overall in our hands. Combining the assays detecting NC and S1/S2 antibody increased diagnostic yield. A portfolio of next generation SARS-CoV-2 immunoassays will be necessary in any future studies of herd and vaccine induced immunity.