Evaluation and clinical implications of the time to a positive results of antigen testing for SARS-CoV-2

J Infect Chemother. 2022 Feb;28(2):248-251. doi: 10.1016/j.jiac.2021.10.026. Epub 2021 Nov 10.

Abstract

Introduction: Antigen tests for severe acute respiratory coronavirus 2 sometimes show positive lines earlier than their specified read time, although the implication of getting the results at earlier time is not well understood.

Methods: We prospectively collected additional nasopharyngeal samples from patients who had already tested positive for SARS-CoV-2 by reverse transcription PCR. The swab was used for an antigen test, QuickNavi™-COVID19 Ag, and the time periods to get positive results were measured.

Results: In 84 of 96 (87.5%) analyzed cases, the results of QuickNavi™-COVID19 Ag were positive. The time to obtain positive results was 15.0 seconds in median (inter quartile range: 12.0-33.3, range 11-736) and was extended in samples with higher cycle thresholds (p < 0.001). Positive lines appeared within a minute in 85.7% of cases and within 5 min in 96.4%.

Conclusion: QuickNavi™-COVID19 Ag immediately showed positive results in most cases, and the time to a positive reaction may have indicated the viral load.

Keywords: Antigen test; COVID-19; QuickNavi™-COVID19 Ag; SARS-CoV-2; Time to positive results.

MeSH terms

  • COVID-19*
  • Diagnostic Tests, Routine
  • Humans
  • Nasopharynx
  • SARS-CoV-2*
  • Sensitivity and Specificity