Accuracy of Expired BinaxNOW Rapid Antigen Tests (preprint)

The widespread existence of expired antigen testing kits in households and potential coronavirus outbreaks necessitate evaluating the reliability of these expired kits. Our study examined BinaxNOW COVID-19 rapid antigen tests 27 months post-manufacture 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. 100 expired and unexpired kits were tested at each concentration for a total of 400 antigen tests. At the LoD (2.32x10^2 TCID50/mL), both expired and unexpired tests displayed 100% sensitivity (95% 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 antigens tests at 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.

Assessment of the Performance of Expired and Unexpired BinaxNOW COVID Rapid Antigen Test Kits Using Positive and Negative Controls (preprint)

Rapid antigen tests are widely used to diagnose infection with SARS-CoV-2, and millions of kits have been distributed for free by government agencies. However, unused and expired kits beyond their final expiration dates remain prevalent in people's homes. This study aimed to determine the accuracy of expired BinaxNOW COVID rapid antigen test kits. 100 expired and 100 unexpired test kits were checked for sensitivity and specificity using positive and negative controls, respectively. The results showed that there was no change in the sensitivity and specificity of BinaxNOW COVID rapid antigen test kits four months beyond the manufacturer-extended expiration date when using manufacturer-provided positive controls. The findings provide confidence in the accuracy of expired test kits, which could potentially reduce waste and strengthen supply chain resilience for pandemic preparedness. Further research utilizing actual human specimens can help determine the true accuracy of expired rapid antigen test kits in clinical use.