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

Abstract

Introduction The development of SARS‐CoV‐2 serological tests is massive. The external validation of their performance is needed before use in clinical routine practice. Objectives Our study aims at assessing the analytical and clinical performance of 2 ELISA tests detecting antibodies directed against the virus nucleocapsid protein: The NovaLisa® SARS‐CoV‐2 IgG, IgA, and 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). Methods Two hundred and eight COVID‐19 samples from 48 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 ROC curves, adapted cut‐off for improvement of the performances were proposed. The kinetics of these antibodies was also assessed over 8 weeks. Results Two weeks after the RT‐qPCR positive detection, the NovaLisa® test shows a sensitivity and specificity of 94.9% (95%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. Conclusion 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.