The SARS-CoV-2 pandemic continues to spread, largely uncontrolled in some regions. Efforts such mask wearing and physical distancing have become politicized, rather than simply viewed as mitigation and containment measures to reduce ongoing transmission. Clinical and public health laboratories have faced incredible challenges with sourcing supplies and reagents  and staff burnout related to record test volumes. Some experts have suggested using antigen tests for more frequent, less expensive testing at the point-of-care .
The BinaxNOW COVID-19 antigen test was granted EUA from the FDA on August 26, 2020, and intended for use in patients within the first 7 days of symptom onset . This lateral flow immunochromatographic assay emplys antibodies specific to antigens expressed in the nucelocapsid protein of SARS-CoV-2. Unlike other antigen-based tests, this is read visually and requires no equipment or instrumentation. Reports on the performance characteristics of the BinaxNOW RDT have been mixed. Notably when first released, the RDT had a 97.1% PPA when compared to an EUA RT-PCR assay . Subsequently, the BinaxNOW RDT has also been made available for prescription home use with a self-collected swab, and demonstrated a 91.7% PPA compared to RT-PCR . Since the initial release, the manufacturer has amended the performance characteristics as a result of larger prospective trials. The product insert now indicates a PPA for the RDT is 84.6% compared to RT-PCR.
In our study, we noted a significantly lower PPA of 68% compared to the data reported by the manufacturer. Our findings are similar to others. In one study involving 2,339 healthcare workers, the BinaxNOW had a sensitivity and specificity of 56.6% and 99.9%, respectively . In a sub-group analysis, the reported sensitivity was 83.3% among symptomatic patients. In another study at two community testing sites, the reported overall sensitivity of the RDT was 52.5%, with an increase to 64.2% among symptomatic patients . We had no RDT positives in our asymptomatic healthcare workers, and are unable to make conclusions of its performance. We also identified that RDT results are more likely to be discordant with NAAT results with higher CN. Our observation is consistent with findings from other recent studies [17, 18].
Frequent antigen testing has been suggested as one alternative to identify contagious patients at risk for spreading SARS-CoV-2 . Some suggest samples with high CN or cycle thresholds but negative antigen results are presumably non-infectious. However, There are conflicting data in the literature, and replication-competent virus has been cultured from symptomatic and asymptomatic persons with a range of cycle thresholds as determined by NAAT [16, 20].
Our study does have limitations. First we enrolled a small number participants, therefore our findings may not be generalizable. Second, we did not perform repeat antigen testing in patients with discordant results, therefore we are unable to assess the utility in more frequent antigen testing to identify patients that subsequently develop COVID-19. In conclusion, our results indicate that the BinaxNOW can reliably detects SARS-CoV-2 viral antigens in specimens with high concentrations of viral RNA.