Clinical And Analytical Performance Of An Automated Serological Test That Identifies S1/S2 Neutralizing IgG In COVID-19 Patients Semiquantitatively

J Clin Microbiol. 2020 Jun 24;JCM.01224-20. doi: 10.1128/JCM.01224-20. Online ahead of print.


Background: In the COVID-19 pandemic, highly selective serological testing is essential to define exposure to SARS-CoV-2 virus. Many tests have been developed, yet with variable speed to first result, and of unknown quality, particularly when considering the prediction of neutralizing capacity.

Objectives/methods: 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 chemiluminescent assay. Clinical and analytical performance of the test were validated in an observational study using residual samples (>1500) with positive or negative COVID-19 diagnosis.

Results: The LIAISON® SARS-CoV-2 S1/S2 IgG assay proved to be highly selective and specific, and offers semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The assay's diagnostic sensitivity was 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 <5 % coefficient of variation. Assay performance at 2 different cut-offs was evaluated to optimize predictive values.

Conclusions: 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 minutes 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 plasma for safe therapeutic use.