Evaluation of the Elecsys SARS-CoV-2 antigen assay for the detection of SARS-CoV-2 in nasopharyngeal swabs.

https://doi.org/10.1016/j.jcv.2021.104991Get rights and content

Highlights

  • Antigen assays for the detection of SARS-CoV-2 are relatively inexpensive and take less time than RT-PCR.

    The automated Elecsys® SARS-CoV-2 antigen was evaluated compared to the gold standard RT-PCR

  • Overall sensitivity of the automated Ag test was 65,85% but could be increased to 100% for Ct values < 25, overall specificity was 100%.

  • The automated Elecsys antigen assay performance should be improved prior to be used in a SARS-Cov-2 screening strategy.

Abstract

Aims

The aim of this study was to evaluate the performance of the automated Elecsys® SARS-CoV-2 antigen assay compared to RT-PCR taken as the gold standard for SARS-CoV-2 detection.

Methods

225 nasopharyngeal swabs were randomly collected among which 123 were tested positive and 102 negatives for SARS-CoV-2 based on RT-PCR. Antigen dosing were performed on a Cobas 8000 e801 analyzer.

Results

The antigen test diagnosed SARS-CoV-2 infection status with an overall sensitivity of 65,85% (95% CI 56,76–74,16%), a specificity of 100% (95% CI 96,49–100%) with a Cut-off value ≥ 1. When the cut-off value for the antigen assay was set to > 0,673 COI, the accuracy reached its highest level with a sensitivity of 74,8% (95% CI 66,2 – 82,2%) and a specificity of 97,1% (95% CI 91,6 – 99,4%). Imprecision was estimated in accordance with manufacturer's claims.

Conclusions

We obtained an overall sensitivity of 65,85% (95% CI 56,76–74,16%) and a specificity of 100% (95% CI 96,49–100%), slightly higher than the results reported by the manufacturer. Yet, it remains relatively low comparatively to what is generally acceptable for these antigenic assays (a relative sensitivity of 80%). We also noticed that the accuracy could reach its highest level if the cut-off is set above 0,673 which is lower than established by the manufacturer. Thus, our results suggest that the Elecsys® SARS-CoV-2 Antigen assays, should be improved prior to be used in a SARS-Cov-2 screening strategy. However, if one antigenic assay could demonstrate acceptable performance, it might be centralized in clinical laboratories, keeping the RT-PCR in a second phase for confirmation.

Keywords

Automated antigen immunoassay
Sensitivity
SARS-CoV-2 testing strategy
COVID-19

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