Clinical and Analytical Performance of an Automated Serological Test That Identifies S1/S2-Neutralizing IgG in COVID-19 Patients Semiquantitatively

Fabrizio Bonelli, Antonella Sarasini, Claudia Zierold, Mariella Calleri, Alice Bonetti, Chiara Vismara, Frank A. Blocki, Luca Pallavicini, Alberto Chinali, Daniela Campisi, Elena Percivalle, Anna Pia DiNapoli, Carlo Federico Perno, Fausto Baldanti

Research output: Contribution to journalArticlepeer-review


In the coronavirus (CoV) disease 2019 (COVID-19) pandemic, highly selective serological testing is essential to define exposure to severe acute respiratory syndrome CoV 2 (SARS-CoV-2). Many tests have been developed, yet with variable speeds to first results, and are of unknown quality, particularly when considering the prediction of neutralizing capacity. The LIAISON SARS-CoV-2 S1/S2 IgG assay was designed to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized automated chemiluminescence assay. The clinical and analytical performances of the test were validated in an observational study using residual samples (>1,500) with a positive or negative COVID-19 diagnosis. The LIAISON SARS-CoV-2 S1/S2 IgG assay proved to be highly selective and specific and offered semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The assay's diagnostic sensitivities were 91.3% and 95.7% at >5 or ≥15 days from diagnosis, respectively, and 100% when assessed against a neutralizing assay. The assay's specificity ranged between 97% and 98.5%. The average imprecision of the assay was a <5% coefficient of variation. Assay performance at 2 different cutoffs was evaluated to optimize predictive values. The automated LIAISON SARS-CoV-2 S1/S2 IgG assay brings efficient, sensitive, specific, and precise serological testing to the laboratory, with the capacity to test large amounts of samples per day; first results are available within 35 min, with a throughput of 170 tests/hour. The semiquantitative results provided by the test also associate with the presence of neutralizing antibodies and may provide a useful tool for the large-scale screening of convalescent-phase plasma for safe therapeutic use.

Original languageEnglish
JournalJournal of Clinical Microbiology
Issue number9
Publication statusPublished - Aug 24 2020


  • CLIA
  • COVID-19
  • diagnostics
  • immunoassays
  • immunoserology
  • neutralization assay
  • neutralizing antibodies
  • SARS-CoV-2
  • spike

ASJC Scopus subject areas

  • Microbiology (medical)


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