Comparison of two fully automated tests detecting antibodies against nucleocapsid N and spike S1/S2 proteins in COVID-19

Flinck, Heini; Rauhio, Anne; Luukinen, Bruno; Lehtimäki, Terho; Haapala, Anna-Maija; Seiskari, Tapio; Aittoniemi, Janne

Automated assays for detecting SARS-CoV-2 antibodies in COVID-19 diagnostics have recently come available. We compared the performance of the Elecsys® Anti-SARS-CoV-2 and LIAISON® SARS-CoV-2 S1/S2 IgG tests. The seroconversion panel comprised of 120 samples from 13 hospitalized COVID-19 patients. For the sensitivity and specificity testing, samples from COVID-19 outpatients >15 days after positive NAAT result (n = 35), and serum control samples collected before the COVID-19 era (n = 161) were included in the material. Samples for the detection of possible cross-reactions were also tested. Based on our results, the SARS-CoV-2 antibodies can be quite reliable detected 2 weeks after NAAT positivity and 3 weeks after the symptom onset with both tests. However, since some COVID-19 patients were positive only with Elecsys®, the antibodies should be screened against N-antigen (Elecsys®), and reactive samples confirmed with S antigen (LIAISON®), but the both results should be reported. In some COVID-19 patients the serology can remain negative.