2022 Volume 71 Issue 2 Pages 250-256
Purpose and method: We determined whether the quantitative antigen test (LUMIPULSE SARS-CoV-2 antigen test) can be used as a screening test for asymptomatic patients and as a negative confirmation test at discharge. In this study, we compared the quantitative antigen and RT-PCR tests in hospitalized patients diagnosed as having COVID-19 from whom two nasopharyngeal swabs were collected at the same time (n = 156). We also examined the negative confirmation and estimation of infectivity based on the amount of antigen. Results: The positive agreement rate of the quantitative antigen test was 97.4% (111/114), the negative agreement rate was 42.9% (18/42), and the overall agreement rate was 82.7% (129/156). In the negative confirmation, the cut-off value of the amount of antigen corresponding to a negative finding by the RT-PCR test was 8.82 pg/mL. In the estimation of infectivity, the cut-off value of the amount of antigen corresponding to the Ct value of ≥ 35 was 89.73 pg/mL. Discussion: The cut-off value of the amount of antigen determined by the quantitative antigen test in the negative confirmation of COVID-19 patients was 8.82 pg/mL, which was higher than the cut-off value of 1.34 pg/mL recommended by the manufacturer. Therefore, if 1.34 pg/mL is used as the cut-off value for negative confirmation in COVID-19 patients, the quantitative antigen test may take longer to show a negative result than the RT-PCR test. In addition, the cut-off value of the amount of antigen corresponding to the Ct value of ≥ 35 was 89.73 pg/mL in the estimation of the infectivity of the virus. In estimating the infectivity based on the amount of antigen, further studies including virus culture are necessary.
