Measurement of anti-SARS-CoV-2 antibodies nucleocapsid versus spike, ECLIA versus ELISA

Objective: The aim of this study is to provide information on the comparison of the determination anti-SARS-CoV-2 antibodies by two differently designed assays, ECLIA (Roche Diagnostics) and ELISA (Euroimmun). Settings: Department of Clinical Biochemistry and Immunology Laboratory, Thomayer University Hospital Materials and Methods: We selected 134 serum samples from 90 patients, Thomayer Hospital staff, and convalescent plasma donors (33 PCR-negative and 57 PCR-positive) at various intervals from the onset of clinical symptoms (1-136 days). We examined anti-SARS-CoV-2 antibodies simultaneously by ELISA in the IgG and IgA classes (DSX) and ECLIA (Cobas e602) and statistically processed the results. By measuring control materials, positive and negative pools we evaluated selected analytical characteristics. Results: We found a high degree of agreement between ELISA and ECLIA. Specificity and sensitivity were very high in both tests, the sensitivity increasing with the distance from the beginning of the symptoms with a maximum of more than 20 days. For ECLIA, the sensitivity may be further increased by application an optimized cut-off. Antibodies persisted to a high degree after 60 days from the onset of symptoms, especially in the IgG class. Intermediate precision and repeatability suited clinical purposes. Conclusion: Both methods are very useful serological monitoring of the antibody response status to SARS-CoV-2 infection. ECLIA method using a highly immunogenic nucleocapsid antigen that captures high affinity antibodies of all classes is preferable for daily routine and the rapid screening. ELISA tests with a conservative spike protein can then be used to confirm and distinguish individual immunoglobulin classes.