Should rapid antigen tests be first-line for COVID-19 testing? Results of a prospective urban cohort study

BACKGROUND: A highly accurate, rapid, and low-cost COVID-19 test is essential for guiding isolation measures. To date, the most widely used tests are either nucleic acid amplification tests or antigen tests. The objective of this study is to further assess the diagnostic performance of the Binax-CoV2 rapid antigen test in comparison to the current gold standard reverse transcription quantitative polymerase chain reaction (RT-qPCR), with additional analysis of symptomatology and cycle threshold utility. METHODS: This is a prospective cohort study performed between November and December 2020. Individuals who presented to COVID-19 testing events and received both RT-qPCR and a rapid antigent test were included. Testing occurred at the emergency department of an urban hospital and at a community mobile unit. No fees or appointments were required. Individuals self-reported the presence or absence of symptoms and history of positive COVID-19 test within the previous two weeks. Trained staff collected two subsequent nasopharyngeal swabs of both nares. One set of swabs underwent RT-qPCR and the other underwent Binax-CoV2 assay per manufacturer guidelines. RESULTS: A total of 390 patients were included, of which 302 were from the community site. Of these 302, 42 (14%) were RT-qPCR positive. Of the 42 RT-qPCR positive, 30 (71.4%) were also positive by Binax-CoV2. The Binax-CoV2 test had a sensitivity of 71.4% (95% CI: 55%–84%) and a specificity of 99.6% (95% CI: 98%–100%) in this population. Performance of the Binax-CoV2 test performed better in individuals with higher viral load. For symptomatic patients with cycle threshold < 20, sensitivity reached 100%. CONCLUSIONS: The Binax-CoV2 assay’s specificity and sensitivity in individuals with high viral load makes it a suitable first-line test for detecting COVID-19. However, given the assay’s measured sensitivity, a negative result on the Binax-CoV2 assay may warrant additional testing with more sensitive tests, such as the RT-qPCR. This is particularly the case with high clinical suspicion for an active SARS-CoV-2 infection even after a negative Binax-CoV2 result.