Background: Molecular detection of SARS-CoV-2 in respiratory samples is the gold standard for COVID-19 diagnosis but it has a long turnaround time and struggles to detect low viral loads. Serology could help to diagnose suspected cases which lack molecular confirmation. Two case reports are presented as illustration.
Objectives: The aim of this study was to evaluate the performance of several commercial assays for COVID-19 serology. We illustrated the added value of COVID-19 serology testing in suspect COVID-19 cases with negative molecular test.
Study design: Twenty-three sera from 7 patients with a confirmed molecular diagnosis of SARS-CoV-2 were tested using 14 commercial assays. Additionally, 10 pre-pandemic sera and 9 potentially cross-reactive sera were selected. We calculated sensitivity and specificity. Furthermore, we discuss the diagnostic relevance of COVID-19 serology in a retrospective cohort of 145 COVID-19 cases in which repetitive molecular and serological SARS-CoV-2 tests were applied.
Results: The interpretation of the pooled sensitivity of IgM/A and IgG resulted in the highest values (range 14-71% on day 2-7; 88-94% on day 8-18). Overall, the specificity of the assays was high (range 79-100%). Among 145 retrospective cases, 3 cases (2%) remained negative after sequential molecular testing but positive on final SARS-CoV-2 serology.
Conclusion: Sensitivity of COVID-19 serological diagnosis was variable but consistently increased at >7 days after symptom onset. Specificity was high. Our data suggest that serology can complement molecular testing for diagnosis of COVID-19, especially for patients presenting the 2nd week after symptom onset or later.
Keywords: COVID-19; SARS-CoV-2; diagnosis; performance; serology.