At-home COVID-19 antigen tests have become a common tool for individuals to quickly check for SARS-CoV-2 infection. A frequent question arises when these tests approach or pass their printed expiration date. Understanding the accuracy of these tests is important for individual health decisions and public health.
Understanding Test Expiration
COVID-19 antigen tests rely on biological components, primarily antibodies and chemical reagents, to detect the virus. These sensitive materials degrade over time, leading to expiration dates.
Environmental factors such as temperature, humidity, and chemical instability can accelerate this degradation. For instance, antibodies can lose their ability to effectively capture viral antigens. Similarly, the liquid solutions in the test kits might evaporate, leading to insufficient volume for the test to run properly. Manufacturers establish these expiration dates based on stability studies to ensure proper performance.
Accuracy and Reliability of Expired Tests
Using an expired COVID-19 test increases the potential for inaccurate results, especially false negatives. This occurs because the degraded components, such as the antibodies, may no longer effectively bind to the viral antigen. The chemical reaction necessary for a positive result might not occur, or the signal might be too weak to be detected, resulting in a negative reading despite the virus’s presence.
A false negative result carries several implications, as an individual might unknowingly spread the virus to others. It can also delay appropriate medical care or isolation measures, potentially worsening symptoms or contributing to community transmission. While an expired test is more likely to yield a false negative, a positive result from an expired test is generally considered reliable. This is because if the test components are degraded, they are less likely to produce any signal, making a positive indication more significant.
Official Guidance and Practical Advice
Health authorities generally advise against using COVID-19 tests past their expiration date. However, first check if the expiration date for your specific test kit has been extended by regulatory bodies. Many manufacturers have conducted additional stability studies, leading the Food and Drug Administration (FDA) to authorize extended expiration dates for numerous at-home COVID-19 tests. This information is typically available on the FDA’s website, where you can search by manufacturer and test name to verify if your test’s shelf life has been updated.
If your test’s expiration date has not been extended, it is best to use a new, unexpired test. If you have used an expired test and received a negative result but still experience symptoms or have had a known exposure, retesting with an unexpired test is recommended. Proper storage, usually within a specific temperature range and away from extreme heat or humidity, also helps maintain the test’s integrity.