Prospective Study of 1,308 Nasopharyngeal Swabs from 1,033 Patients using the LUMIPULSE SARS-CoV-2 Antigen Test: Comparison with RT-qPCR

Hirotsu, Yosuke; Maejima, Makoto; Shibusawa, Masahiro; Amemiya, Kenji; Nagakubo, Yuki; Hosaka, Kazuhiro; Sueki, Hitomi; Hayakawa, Miyoko; Mochizuki, Hitoshi; Tsutsui, Toshiharu; Kakizaki, Yumiko; Miyashita, Yoshihiro; Omata, Masao

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.