Finding an older COVID-19 rapid antigen test kit with a passed expiration date is common. While the impulse may be to discard the test to avoid unreliable results, the core conflict centers on the need for timely, accurate results versus the potential for test components to degrade over time. The reliability of the test’s result is the most important factor when considering its functionality beyond the date printed on the box.
The Science of Test Expiration
COVID-19 rapid antigen tests rely on sensitive biological and chemical components that determine their shelf life. The test cassette contains specific antibodies, often linked to tiny gold nanoparticles, which are designed to bind precisely with SARS-CoV-2 proteins, creating the visible line on the test strip. Manufacturers initially establish expiration dates using stability studies, which predict how long these active components will maintain their effectiveness under ideal storage conditions.
Over an extended period, the antibodies printed on the test strip can chemically degrade, reducing their ability to accurately capture the viral protein from a sample. The liquid buffer solution, which helps extract the virus from the swab and facilitates the flow across the test strip, can also lose its chemical stability. When these components break down, the test’s sensitivity is compromised, meaning it may not detect the virus even if it is present, resulting in a false negative result. The initial expiration date ensures the test delivers results with the same accuracy as when it was first manufactured.
Checking for Authorized Expiration Date Extensions
The printed expiration date on the box is often not the final word on a test’s validity. Manufacturers have conducted further stability testing since initial production, demonstrating that test components remain stable and functional longer than originally estimated. Based on this evidence, regulatory bodies have officially granted extensions to the shelf life for specific brands and manufacturing lots.
To determine the true, current expiration date, you must perform a precise verification process. First, locate the test’s brand name and the specific lot number, typically printed on the side or bottom of the test box near the original expiration date. Next, check the relevant government website for a list of authorized at-home tests that have received shelf-life extensions.
The regulatory agency’s list often contains links or tables where you can search for your test’s specific lot number and compare it against the newly authorized expiration date. If your lot number appears on the official extension list, you can rely on the extended date, even if it is months or years past the one printed on the packaging. If the lot number is not listed, or if the test has passed the extended date, it is recommended to discard the kit.
The Role of Proper Test Storage
Even an unexpired or officially extended test can become unreliable if it has not been stored correctly. The integrity of the test’s chemical components is highly sensitive to environmental factors, particularly temperature extremes. Most rapid antigen tests are designed to be stored at room temperature, typically defined as between 59 and 86 degrees Fahrenheit.
Exposing the test kit to temperatures outside this range can rapidly compromise the reagents. For instance, leaving a test in a freezing mailbox overnight or in a scorching hot car during the summer can immediately damage the liquid buffer and the antibody-coated test strip. Once the reagents are damaged by heat or cold, the test’s performance is permanently affected, regardless of the printed or extended expiration date. Following the specific storage instructions is necessary to ensure the test performs as intended.
Interpreting Results from an Expired Test
If a person decides to use a test that is past its official, extended expiration date, the way they interpret the results must be adjusted due to the risk of reduced sensitivity. The primary concern is the possibility of a false negative result, where the test incorrectly indicates no infection. This risk is elevated because the chemical degradation of the test’s components makes it less effective at binding to and detecting lower concentrations of the viral protein.
In contrast, if an expired or compromised test returns a positive result, it is considered reliable. A positive line indicates that enough viral antigen was successfully detected to trigger the reaction, confirming the presence of the virus. If the result is negative, however, and the user has symptoms consistent with a COVID-19 infection, the result should be viewed with skepticism. In this scenario, the individual should seek retesting with a new, unexpired kit or confirm the result with a laboratory-based test.