Analytical and clinical validation of an ELISA for specific SARS‐CoV‐2 IgG, IgA, and IgM antibodies

Abstract

The development of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) serological tests is massive. The external validation of their performance is needed before use in clinical routine practice. Our study aims at assessing the analytical and clinical performance of two enzyme‐linked immunosorbent assay tests detecting antibodies directed against the virus nucleocapsid protein: The NovaLisa SARS‐CoV‐2 immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin M (IgM) test (NovaTec) allowing a separate detection of each antibody and the Platelia SARS‐CoV‐2 Total Ab test (Bio‐Rad) detecting total antibodies (IgM, IgA, and IgG). Two‐hundred and eight coronavirus disease 2019 samples from 48 quantitative reverse transcription‐polymerase chain reaction (RT‐qPCR) confirmed patients were used to perform the sensitivity analysis. Non‐SARS‐CoV‐2 sera (n = 79) with a potential cross‐reaction to SARS‐CoV‐2 immunoassays were included in the specificity analysis. In addition, using receiver operator characteristic curves, adapted cut‐off for improvement of the performances were proposed. The kinetics of these antibodies was also assessed over 8 weeks. Two weeks after the RT‐qPCR positive detection, the NovaLisa test shows a sensitivity and specificity of 94.9% (95% confidence interval [CI]: 83.1%‐98.6%) and 96.2% (95% CI: 89.4%‐98.7%) for IgG, of 89.7% (95% CI: 76.4%‐95.9%) and 98.7% (95% CI: 93.2%‐98.8%) for IgA, and of 48.7% (95% CI: 33.9%‐63.8%) and 98.7% (95% CI: 93.2%‐99.8%) for IgM. With the Platelia system, the specificity and sensitivity were 97.4% (95% CI: 92.1%‐99.7%) and 94.9% (95% CI: 87.7%‐98.0%) for total antibodies using the adapted cut‐offs. The NovaLisa and the Platelia tests have satisfactory analytical performances. The clinical performances are excellent for IgG, IgA, and total antibodies especially if the cut‐off is optimized.

SARS-CoV-2 Antibody Responses Are Correlated to Disease Severity in COVID-19 Convalescent Individuals

“…This suggests that a majority of individuals are lacking an early response from IgA rather than IgM. We have compared our results with a previously published report (23), in which the sensitivity for IgA and IgM for protein N are substantially higher than our results. These discordances might be explained by the different cohort samples employed in both reports.…”

Results of the first pilot external quality assessment (EQA) scheme for anti-SARS-CoV2-antibody testing

“…The analytical variability of anti-SARS-CoV-2 IgG testing between different methods did not differ substantially. This indicates that harmonization of test results from different providers could be achieved by optimizing cutoffs, as recently supposed by Plebani et al and others [14,[28][29][30]. Interestingly, some results reported by laboratories using the same commercial test system differed substantially.…”

Multi-species ELISA for the detection of antibodies against SARS-CoV-2 in animals

“…For human sera, a wide range of ELISA systems have been developed within a very short time based on different antigens that include the viral nucleocapsid (N) protein, the spike protein (S) or the S receptor-binding domain (RBD) (Beavis et al, 2020; Klumpp-Thomas et al, 2020; Tré-Hardy et al, 2020). When comparing different antigens as assay targets, considerable cross-reactivity between different coronaviruses occurred in whole-virus or N-based serological assays, while S or RBD based protocols demonstrated a much higher specificity (Chia et al, 2020; Klumpp-Thomas et al, 2020; Meyer, Drosten, & Müller, 2014).…”