Association of the Serum Levels of the Nucleocapsid Antigen of SARS-CoV-2 With the Diagnosis, Disease Severity, and Antibody Titers in Patients With COVID-19: A Retrospective Cross-Sectional Study

• Published in: Frontiers in microbiology Vol. 12; p. 791489
• Main Authors: Yokoyama, Rin, Kurano, Makoto, Nakano, Yuki, Morita, Yoshifumi, Ohmiya, Hiroko, Kishi, Yoshiro, Okada, Jun, Qian, Chungen, Xia, Fuzhen, He, Fan, Zheng, Liang, Yu, Yi, Mizoguchi, Miyuki, Higurashi, Yoshimi, Harada, Sohei, Jubishi, Daisuke, Okamoto, Koh, Moriya, Kyoji, Kodama, Tatsuhiko, Yatomi, Yutaka
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 09.12.2021
• Subjects: coronavirus disease 2019; COVID-19; diagnosis; Microbiology; N antigen; nucleocapsid antigen; severity; COVID-19; severity; antibody titer; nucleocapsid antigen; coronavirus disease 2019; N antigen; diagnosis
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2021.791489

Several types of laboratory tests for COVID-19 have been established to date; however, the clinical significance of the serum SARS-CoV-2 nucleocapsid (N) antigen levels remains to be fully elucidated. In the present study, we attempted to elucidate the usefulness and clinical significance of the serum N antigen levels. We measured the serum N antigen levels in 391 serum samples collected from symptomatic patients with a confirmed diagnosis of COVID-19 and 96 serum samples collected from patients with non-COVID-19, using a fully automated chemiluminescence immunoassay analyzer. Receiver operating characteristic analysis identified the optimal cutoff value of the serum N antigen level (cutoff index, based on Youden's index) as 0.255, which yielded a sensitivity and specificity for the diagnosis of COVID-19 of 91.0 and 81.3%, respectively. The serum N antigen levels were significantly higher in the patient groups with moderate and severe COVID-19 than with mild disease. Moreover, a significant negative correlation was observed between the serum N antigen levels and the SARS-CoV-2 IgG antibody titers, especially in patients with severe COVID-19. Serum N antigen testing might be useful both for the diagnosis of COVID-19 and for obtaining a better understanding of the clinical features of the disease.