Head-to-head comparison of two rapid high-throughput automated electrochemiluminescence immunoassays targeting total antibodies to the SARS-CoV-2 nucleoprotein and spike protein receptor binding domain

Poljak, Mario; Valenčak, Anja Oštrbenk; Štamol, Tina; Seme, Katja

BACKGROUND: Accurate anti-SARS-CoV-2 assays are needed to inform diagnostic, therapeutic, and public health decisions. The first manufacturer-independent head-to-head comparison of two rapid high-throughput automated electrochemiluminescence double-antigen sandwich immunoassays targeting total anti-SARS-CoV-2 antibodies against two different viral proteins, Elecsys Anti-SARS-CoV-2 (Elecsys-N) and Elecsys Anti-SARS-CoV-2 S (Elecsys-S) (Roche Diagnostics), was performed in a routine setting during the exponential growth phase of the epidemic’s second wave. METHODS: The diagnostic specificity of Elecsys-N and Elecsys-S was initially evaluated on a panel of 572 pre-COVID-19 samples, showing 100% specificity of both assays. Elecsys-N/Elecsys-S head-to-head comparison used 3,416 consecutive blood samples from individuals that were tested for the presence of anti-SARS-CoV-2 within commercial out-of-pocket serologic testing. RESULTS: Elecsys-N/Elecsys-S head-to-head comparison showed overall agreement of 98.68% (3,371/3,416; 95% CI, 98.23–99.03%), positive agreement of 95.16% (884/929; 95% CI, 93.52–96.41%), and a high kappa value of 0.996 (95% CI, 0.956–0.976). Previous SARS-CoV-2 PCR positivity was identified in 14/24 (58.3%) Elecsys-N negative/Elecsys-S positive individuals and in 4/21 (19.0%) Elecsys-N positive/Elecsys-S negative individuals. CONCLUSION: The first Elecsys-N/Elecsys-S head-to-head comparison showed excellent agreement of two highly specific and rapid high-throughput automated anti-SARS-CoV-2 assays. An important question is whether laboratories offering two different antibody assays could benefit from combining the assays; if so, should use be concomitant or sequential—and, in the latter case, in which order? Based on our results, we favor concomitant over sequential Elecsys-N/Elecsys-S use when testing individuals for anti-SARS-CoV-2 antibodies in high-incidence settings; for example, during the exponential or stationary growth phase of the COVID-19 epidemic.