Diagnostic Accuracy of Four Serological Tests for COVID-19 and Differences in Antibody Positivity Rates Based on the Need for Treatment or Ventilator Support

Abstract

Nucleic-acid amplification test (NAT), routinely used for diagnosing coronavirus disease 2019 (COVID-19), is associated with false negative results. Alternatively, serological tests detect antibodies produced against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19. Here, we evaluated the diagnostic accuracy of a single quantum dot immunoassay and three lateral flow immunoassays for COVID-19. We also assessed differences in the antibody positivity rates between patients receiving and not receiving ventilator support and between those treated and not treated with antiviral agents and/or corticosteroids. Test accuracy was estimated by measuring the sensitivity and specificity using receiver operating characteristic curves, along with NAT; sensitivity of NAT was 68.0% (95% confidence interval [CI]: 46.5-85.1%). IgM and IgG serological test sensitivities varied from 20.0% (95% CI: 6.83-40.7%) to 100% (95% CI: 86.3-100%) and from 84% (95% CI: 63.9-95.5%) to 100% (95% CI: 86.3-100%), respectively. The nucleocapsid protein-based serological test sensitivity was up to 100% for IgM and IgG. Serological test positivity rates were higher in patients receiving ventilator support and treatment than in patients not receiving ventilator support and treatment; the positivity rates were significantly higher for IgM than for IgG with the quantum dot immunoassay (Mokobio Biotechnology; 58.3% vs. 15.5%, P＜0.05) and one of the lateral flow immunoassays (Kurabo: 83.3% vs. 30.8%, P＜0.05). Thus, accuracy of serological tests varied depending on the test kit used; nonetheless, some serological test kits might be helpful as a complementary tool in COVID-19 diagnosis. And quantitative assessment of IgM levels may be useful in predicting the severity of the disease and in determining the course of treatment.