Validation of cutoff index for diagnosing COVID-19 using HISCL^TM SARS-CoV-2Ag reagent: Current status and challenges of SARS-CoV-2 Ag test in Nagoya University Hospital

<p>For the effective isolation of SARS-CoV-2 and early treatment of coronavirus disease 2019 (COVID-19), diagnostic methods with improved operating efficiency, flexibility, and the fastest time-to-results with the highest throughput are required. The HISCL^TM SARS-CoV-2 antigen test to screen for SARS-CoV-2-infected persons has been carried out in our hospital. However, the evaluation of data showed some discrepancies in results between the antigen test and the RT-qPCR test. In this study, we evaluated the results of the SARS-CoV-2 antigen test performed in Nagoya University Hospital and validated the cutoff index (C.O.I.) using the obtained measurement data. The optimal C.O.I. was determined using a receiver operating characteristic (ROC) curve. From April 6 to January 31, there were 6,646 routine antigen tests processed, with 71 positive results (1.0 to 47,318.6 C.O.I.). In these tests, 48 patients were diagnosed as having COVID-19, and the rate of positivity concordance between the antigen and RT-qPCR tests was 67.6%. The area under the curve (AUC) was 0.93 and the optimal C.O.I. was 3.95, where the corresponding sensitivity and specificity were 85.4% and 91.3%, respectively. These results suggest that SARS-CoV-2 screening with a positive C.O.I. of 4.0 makes it possible to provide the highest sensitivity while maintaining high specificity with high throughput.</p>