Accuracy of Expired BinaxNOW Rapid Antigen Tests

The widespread existence of expired antigen testing kits in households and potential coronavirus outbreaks necessitates evaluating the reliability of these expired kits. Our study examined BinaxNOW COVID-19 rapid antigen tests 27 months postmanufacture and 5 months past their FDA extended expiration dates, using SARS-CoV-2 variant XBB.1.5 viral stock. We conducted testing at two concentrations, the limit of detection (LOD) and 10 times the LOD. One hundred expired and unexpired kits were tested at each concentration for a total of 400 antigen tests. At the LOD (2.32 × 10² 50% tissue culture infective dose/mL [TCID₅₀/mL]), both expired and unexpired tests displayed 100% sensitivity (95% confidence interval [CI], 96.38% to 100%), with no statistical difference (95% CI, -3.92% to 3.92%). Similarly, at 10 times the LOD, unexpired tests retained 100% sensitivity (95% CI, 96.38% to 100%), while expired tests exhibited 99% sensitivity (95% CI, 94.61% to 99.99%), demonstrating a statistically insignificant 1% difference (95% CI, -2.49% to 4.49%; P = 0.56). Expired rapid antigen tests had fainter lines than the unexpired tests at each viral concentration. The expired rapid antigen tests at the LOD were only just visible. These findings carry significant implications for waste management, cost efficiency, and supply chain resilience in pandemic readiness efforts. They also provide critical insights for formulating clinical guidelines for interpreting results from expired kits. In light of expert warnings of a potential outbreak of a severity rivaling the Omicron variant, our study underscores the importance of maximizing the utility of expired antigen testing kits in managing future health emergencies. IMPORTANCE The study examining the reliability of expired antigen testing kits in the context of COVID-19 has significant real-world implications. By demonstrating that these expired kits retain their sensitivity in detecting the virus, this work provides evidence that expired kits can still be utilized, reducing waste and optimizing resources in health care systems. These findings are especially crucial in light of potential future coronavirus outbreaks and the need to be prepared. The study's outcomes have the potential to contribute to waste management efforts, cost efficiency, and supply chain resilience, ensuring that diagnostic tests remain readily available for effective public health interventions. Furthermore, it provides critical insights for formulating clinical guidelines on interpreting results from expired kits, enhancing the accuracy of testing outcomes, and supporting informed decision-making. Ultimately, this work holds great importance in maximizing the utility of expired antigen testing kits, safeguarding public health, and enhancing pandemic readiness on a global scale.