BACKGROUND: Reverse-transcription PCR (RT-PCR) is the gold standard for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection . Previously, we demonstrated the accuracy of the quantitative LUMIPULSE SARS-CoV-2 antigen test using samples collected retrospectively . Here, the antigen test was clinically validated using prospective samples .

METHODS: A total of 1,033 nasopharyngeal swab samples were collected 1,033 individuals and an additional 275 follow-up samples were collected from 43 patients who later tested positive for COVID-19 . All 1,308 samples were subjected to quantitative RT-PCR (RT-qPCR) and the LUMIPULSE antigen test . Antibody response was investigated for patients with discordant results to clarify whether seroconversion had occurred .

RESULTS: RT-qPCR identified 990 samples as negative and 43 as positive, while the antigen test identified 992 as negative , 37 as positive, and 4 as inconclusive . The overall concordance rate was 99.7% (1,026/1,029). The sensitivity, specificity, positive predictive value and negative predictive value of the antigen test were 92.5% (37/40), 100% (989/989), 100% (37/37) and of 99.7% (989/992), respectively, after excluding the four inconclusive results . The kappa coefficient was 0.960 (95% confidence interval , 0.892-0.960), suggesting excellent agreement between the two tests . The seropositive in five out of the seven patients with discordant results suggested that the discrepancy was caused by samples collected during the late phase of infection . Using the follow-up samples, we observed a correlation between the antigen level and the viral load or threshold cycle (Ct) value . The concordance rate between these test results tended to be high among samples collected up to 9 days after symptom onset but this gradually decreased thereafter .

CONCLUSIONS: This prospective study demonstrated that the LUMIPULSE antigen test is a highly accurate diagnostic for SARS-CoV-2.