Performance of the VITROS (R) Immunodiagnostic Products Sars-Cov-2 Antigen Assay

Background/Case Studies: This study was designed to assess the clinical and analytical performance of the VITROS Immunodiagnostic Products SARS-CoV-2 Antigen assay (VITROS SARS-CoV-2 Antigen) on the VITROS 3600 Immunodiagnostic System and the VITROS 5600/ XT 7600 Integrated Systems. Study Design/Methods: Detection of SARS-CoV-2 nucleocapsid protein in the VITROS SARS-CoV-2 Antigen assay is achieved using monoclonal anti-SARSCoV- 2 nucleocapsid antibodies coated onto the well. Sample is added to the coated well in the first stage of the reaction, and SARS-CoV-2 nucleocapsid antigen from the sample is captured. After washing, HRP conjugated monoclonal anti-SARS-CoV-2 nucleocapsid antibodies are added. Following a final wash, bound HRP conjugates are detected using the VITROS signal reagent. The assay cut-off for VITROS SARS-CoV-2 Antigen is 1.00;values above the cut-off are Reactive for SARS-CoV-2 antigen and values below 1.00 are Non-reactive. All VITROS testing was performed at the Ortho Clinical Diagnostics R&D lab, located in Rochester, NY, USA. RTPCR testing of clinical specimen was performed at an external clinical laboratory. Clinical performance was evaluated using 152 paired nasopharyngeal and nasal specimen that were collected in the United States between September and November 2020. Samples were stored frozen between the time of collection and testing and were from patients suspected of having contracted SARS-CoV-2 within seven days of symptom onset. Data were analyzed to calculate the positive percent agreement (PPA) and negative percent agreement to RT-PCR result. Analytical specificity was assessed by testing patient matrix spiked with inactivated organisms known to cause other respiratory infections. Exogenous compounds with potential to be present in upper respiratory specimen collected from patients suffering from upper respiratory infection were also tested for potential interference with the VITROS assay. Results/Findings: PPA for the VITROS assay in nasopharyngeal specimen was 86.2% overall and 94.8% in samples with RT-PCR cycle threshold (Ct) less than 30. PPA for nasal specimen was 83.1% overall and 92.3% in samples with RT-PCR Ct less than 30. Other respiratory organisms and potentially interfering substances were shown to not impact test results. Conclusions: The VITROS SARS-CoV-2 Antigen assay demonstrates excellent clinical agreement with RT-PCR and can be used as an aid in identifying individuals with active SARS-CoV-2 infection.