Analytical and clinical performances of a SARS-CoV-2 S-RBD IgG assay: comparison with neutralization titers

Clin Chem Lab Med. 2021 Apr 14;59(8):1444-1452. doi: 10.1515/cclm-2021-0313. Print 2021 Jul 27.

Abstract

Objectives: SARS-CoV-2 serology presents an important role in several aspects of COVID-19 pandemic. Immunoassays performances have to be accurately evaluated and correlated with neutralizing antibodies. We investigated the analytical and clinical performances of a SARS-CoV-2 RBD IgG assay, automated on a high throughput platform, and the correlation of the antibodies (Ab) levels with the plaque reduction neutralization (PRNT50) Ab titers.

Methods: A series of 546 samples were evaluated by SARS-CoV-2 RBD IgG assay (Snibe diagnostics), including 171 negative and 168 positive SARS-CoV-2 subjects and a further group of 207 subjects of the COVID-19 family clusters follow-up cohort.

Results: Assay imprecision ranged from 3.98 to 12.18% being satisfactory at low and medium levels; linearity was excellent in all the measurement range. Considering specimens collected after 14 days post symptoms onset, overall sensitivity and specificity were 99.0 and 92.5%, respectively. A total of 281 leftover samples results of the PRNT50 test were available. An elevated correlation was obtained between the SARS-CoV-2 RBD IgG assay and the PRNT50 titer at univariate (ρ=0.689) and multivariate (ρ=0.712) analyses.

Conclusions: SARS-CoV-2 S-RBD IgG assay shows satisfactory analytical and clinical performances, and a strong correlation with sera neutralizing activity.

Keywords: SARS-CoV-2; antibodies; clinical performances; immunoassays; neutralization; plaque reduction neutralization test; serology.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Neutralizing / blood
  • Antibodies, Neutralizing / immunology*
  • Antibodies, Viral / blood
  • COVID-19 / pathology
  • COVID-19 / virology
  • Child
  • Female
  • Humans
  • Immunoassay / methods
  • Immunoglobulin G / blood
  • Immunoglobulin G / immunology*
  • Male
  • Middle Aged
  • Neutralization Tests / methods*
  • Protein Subunits / immunology
  • SARS-CoV-2 / isolation & purification
  • SARS-CoV-2 / metabolism*
  • Severity of Illness Index
  • Spike Glycoprotein, Coronavirus / immunology*
  • Young Adult

Substances

  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Immunoglobulin G
  • Protein Subunits
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2