Clinical Application of a Solid-Phase Assay for SARS-CoV-2 IgG to Predict a Neutralizing Antibody Titer

Yoonjung Kim, Joon Yong Bae, Gee Eun Lee, Heedo Park, Kitae Kwon, Hyun Ha Chang, Jeonghun Kim, Jungmin Lee, Juyoung Cho, Man Seong Park, Shin Woo Kim, Dong Il Won

Research output: Contribution to journalArticlepeer-review


Background: To assess protective immunity among a general population against severe acute respiratory syndrome coronavirus 2, the correlation of the commercially available solid-phase assay (SPA) for SARS-CoV-2 IgG with a neutralization assay must be investigated. Methods: Both the neutralization assay and SPA were performed on samples of 143 recovered coronavirus disease 2019 (COVID-19) patients. SARS-CoV-2 IgG was measured using two SPAs for the chemiluminescence immunoassay principle with different target proteins: nucleocapsid and spike protein (Architect i2000SR [Abbott] and Liaison XL [DiaSorin], respectively). The plaque reduction neutralization test (PRNT) was conducted to obtain titers for the neutralizing antibody. Results: All patients had PRNT titers ranging from 10 to 2,560. Spike Ab SPA had greater sensitivity than nucleocapsid Ab SPA (81.1% [116/143] and 70.6% [101/143], respectively, p = 0.003). The values measured for both SPAs had a positive correlation with the PRNT titers (both R = 0.77, p < 0.001). To predict a high PRNT titer (≥ 160), cutoff values of two SPAs were adjusted based on receiver-operating characteristics curve analysis. The nucleocapsid Ab SPA (cutoff index of 4.17) attained 90.3% sensitivity and 75.9% specificity, whereas the spike Ab SPA (cutoff value of 109 unit/mL) attained 87.1% sensitivity and 89.3% specificity. Therefore, the spike Ab SPA had greater specificity than the nucleocapsid Ab SPA (p = 0.003). Conclusions: The qualitative SPA for nucleocapsid Ab, as well as the quantitative SPA for spike Ab, had a modest positive correlation with the neutralization assay. However, spike Ab SPA was more suitable for neutralizing capacity.

Original languageEnglish
Pages (from-to)1911-1919
Number of pages9
JournalClinical Laboratory
Issue number9
Publication statusPublished - 2022 Sept


  • COVID-19
  • SARS-CoV-2
  • chemiluminescence immunoassay
  • neutralization assay
  • neutralizing antibody

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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