Diagnostic and analytical performance evaluation of ten commercial assays for detecting SARS-CoV-2 humoral immune response

Abstract

Objective: Analytical validation of newly released SARS-CoV-2 antibody assays in the clinical laboratory is crucial to ensure sufficient performance in respect to its intended use. We aimed to assess analytical and diagnostic performance of 8 (semi-)quantitative assays detecting anti-nucleocapsid IgG (Euroimmun, Id-Vet) or total Ig (Roche), anti-spike protein IgG (Euroimmun, Theradiag, DiaSorin, Thermo Fisher) or both (Theradiag) and 2 rapid lateral flow assays (LFA) (AAZ-LMB and Theradiag).

Methods: Specificity was evaluated using a cross-reactivity panel of 85 pre-pandemic serum samples. Sensitivity was determined at both the manufacturer's and a 95% specificity cut-off level, using 81 serum samples of patients with a positive rRT-PCR. Sensitivity was determined in function of time post symptoms onset.

Results: Specificity for all assays ranged from 92.9% to 100% (Roche and Thermo Fisher) with the exception of the Theradiag IgM LFA (82.4%). Sensitivity in asymptomatic patients ranged between 41.7% and 58.3%. Sensitivity on samples taken <10 days since symptom onset was low (23.3%-66.7%) and increased on samples taken between 10 and 20 days and > 20 days since symptom onset (80%-96% and 92.9%-100%, respectively). From 20 days after symptom onset, the Roche, Id-vet and Thermo Fisher assays all met the sensitivity (>95%) and specificity (>97%) targets determined by the WHO. Antibody signal response was significantly higher in the critically ill patient group.

Conclusion: Antibody detection can complement rRT-PCR for the diagnosis of COVID-19, especially in the later stage, or in asymptomatic patients for epidemiological purposes. Addition of IgM in LFAs did not improve sensitivity.

Keywords: Antibody; COVID-19; Humoral response; SARS-CoV-2; Serology.

Fig. 1

Receiver operating characteristic (ROC) curves of all (semi-)quantitative assays according to different sensitivity cohorts. A. Concerning the ‘all sensitivity cohort’ (n = 81), R-N showed significantly higher AUC than any other assay (p < 0.05); DS-S showed significantly lower AUC than any other assay (all p < 0.05) Id-N showed significantly higher AUC than TF-S (p = 0.0465). B. In the sensitivity cohort ‘asymptomatic’ (n = 12), DS-S showed significantly lower AUC than Id-N (p = 0.0357), TD-S (p = 0.0383), R-N (p = 0.0056), TF-S (p = 0.0062) and TD-SN (p = 0.0475); R-N showed significantly higher AUC than EI S (p = 0.0101) and TF-S (p = 0.0286) and Id-N showed significantly higher AUC than TF-S (p = 0.0465). C. In sensitivity cohort ‘<10 days after symptom onset’, DS-S showed significantly lower AUC than any other assay (all p < 0.05); additionally, R-N showed significantly higher AUC than EI S (p = 0.0147), EI N (p = 0.0174), TF-S (p = 0.0161) and TD-SN (p = 0.0067). D. In sensitivity cohort ‘10–20 days after symptom onset’, DS-S showed significantly lower AUC than Id-N (p = 0.0195) and R-N (p = 0.0197). E. Concerning sensitivity cohort ‘≥20 days after symptom onset’ no significantly differences in AUC were revealed (all p > 0.05).