Prospective study of 1308 nasopharyngeal swabs from 1033 patients using the LUMIPULSE SARS-CoV-2 antigen test: Comparison with RT-qPCR

Abstract

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

Methods: In total, 1033 nasopharyngeal swab samples were collected from 1033 individuals, and an additional 275 follow-up samples were collected from 43 patients who subsequently tested positive for coronavirus disease 2019 (COVID-19). All 1308 samples were subjected to quantitative RT-PCR (RT-qPCR) and the antigen test. The antibody response was investigated for patients with discordant results to clarify if seroconversion had occurred.

Results: RT-qPCR identified 990 samples as negative and 43 as positive, while the antigen test identified 992 samples as negative, 37 as positive and four as inconclusive. The overall concordance rate was 99.7% (1026/1029). 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 99.7% (989/992), respectively, after exclusion of the four inconclusive results. The kappa coefficient was 0.960 (95% confidence interval 0.892-0.960), suggesting excellent agreement between the two tests. Seropositivity in five of seven patients with discordant results suggested that the discrepancy was caused by samples collected during the late phase of infection. Using follow-up samples, correlation was observed between the antigen level and the viral load or cycle threshold value. The concordance rate between these test results tended to be high among samples collected 0-9 days after symptom onset, but this decreased gradually in samples collected thereafter.

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

Keywords: Antigen; COVID-19; LUMIPULSE; RT-qPCR; SARS-CoV-2.

Figure 1

Prospective study of the antigen levels in 1033 initial samples collected from 1033 individuals. The dot plots show the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antigen levels in the samples identified by polymerase chain reaction (PCR) as negative (n = 990) or positive (n = 43). Among the 43 PCR-positive individuals, 36 were symptomatic and seven were asymptomatic. The two dashed lines indicate the decision threshold for the LUMIPULSE antigen test. The lower dashed line indicates 0 log₁₀ pg/mL (1 pg/mL) and the upper dashed line indicates 1 log₁₀ pg/mL (10 pg/mL).

Figure 2

Correlation between the antigen level and viral load or threshold cycle (Ct) value. In the study cohort, 43 patients with coronavirus disease 2019 were identified. A total of 318 samples were collected from these patients, including 43 initial and 275 follow-up samples. The dot plots show the correlation between the antigen level as determined in the LUMIPULSE antigen test and the viral load (A) or Ct value (B) as determined on quantitative reverse transcription polymerase chain reaction. SARS-CoV-2, severe acute respiratory syndrome coronavirus-2.

Figure 3

Effect of the timing of sample collection since symptom onset on test results. In total, 250 samples were collected from 36 symptomatic patients with coronavirus disease 2019 for 30 days after symptom onset, and these samples were subjected to both the LUMIPULSE antigen test and quantitative reverse transcription polymerase chain reaction (RT-qPCR). (A) Positive result ratio was calculated by the number of positive samples on RT-qPCR or antigen test during the period since symptom onset divided by the total number of samples tested in that period. (B) The concordance ratio indicates the percentage of samples with equivalent results from the antigen test and RT-qPCR when excluding samples with inconclusive antigen test results.