The widespread use of rapid at-home COVID-19 tests has raised questions about their reliability, particularly as these tests age. Many individuals find themselves with tests approaching or past their printed expiration dates, leading to concerns about the accuracy of the results. This article explains why COVID-19 tests expire, what that means for their accuracy, and how to ensure reliable testing.
Why COVID Tests Expire
COVID-19 rapid antigen tests, much like medications, have a defined shelf life due to the nature of their components. These tests rely on biological reagents, such as antibodies and enzymes, which are susceptible to degradation over time. These antibodies bind to viral proteins (antigens) from SARS-CoV-2, generating a visible positive result.
As these biological components degrade, their ability to accurately detect the virus diminishes. Factors such as exposure to extreme temperatures and high humidity can accelerate this degradation process. The liquid solutions within the test kits can also evaporate, which can affect the test’s ability to function correctly. Manufacturers initially set conservative expiration dates because comprehensive long-term stability data was not immediately available when the tests were first authorized.
Accuracy of Expired Tests
The primary concern with using an expired COVID-19 rapid antigen test is a reduction in its sensitivity, which can lead to false negative results. When the reagents, particularly the antibodies, degrade, they may not effectively bind to the viral proteins even if the virus is present in the sample. This means an expired test might indicate a person is not infected when they actually are, potentially providing a false sense of security.
While the possibility of a false positive from an expired test is generally less common compared to a false negative, it can still occur due to other factors. False positives are more frequently linked to user error during sample collection or test administration, or contamination, rather than the test simply being old. Regardless of the potential direction of error, any result from a test used beyond its confirmed expiration date cannot be considered reliable.
Interpreting Results from an Expired Test
If an expired test yields a positive result, it is advisable to confirm this finding with a new, unexpired test or to seek medical advice for further verification. While some experts suggest that a positive result from an expired test is often accurate if symptoms are present, confirming it with a valid test is the safest approach.
Conversely, if an expired test shows a negative result, it does not reliably rule out an infection, especially if symptoms are present or there has been a known exposure. In such cases, retesting with an unexpired kit is essential to obtain an accurate assessment of one’s COVID-19 status. The U.S. Food and Drug Administration (FDA) advises against using expired tests that have not had their expiration dates officially extended.
Ensuring Reliable COVID Testing
To ensure the most reliable COVID-19 test results, it is important to always check the expiration date on the test kit before use. Many tests have had their expiration dates extended by the FDA. Check the FDA’s website for updated information on specific test brands and lot numbers. If a test’s date has not been extended and it is past its printed expiration, it should not be used.
Proper storage of test kits is also important for maintaining their integrity. Tests should generally be stored within a specific temperature range, typically between 36°F and 86°F (2°C to 30°C), and kept away from extreme heat, cold, or high humidity. Following the manufacturer’s instructions carefully for both storage and test administration is crucial for obtaining accurate results. Reliable, unexpired tests can be obtained from pharmacies, healthcare providers, or through government programs that offer free tests.