Rapid COVID-19 antigen tests are a common, convenient tool for quickly checking for SARS-CoV-2 infection at home. A key question arises about their reliability, especially when used beyond the printed expiration date. These tests are manufactured with a specific shelf life, determined by the stability of their internal components.
Why COVID Tests Expire
COVID-19 rapid antigen tests contain specific chemical reagents and SARS-CoV-2 antigen-specific antibodies designed to detect viral proteins. Over time, these biological materials can degrade, reducing the test’s ability to accurately identify the virus. Manufacturers establish an expiration date based on studies assessing how long these components remain stable and effective. The typical initial shelf life authorized by the FDA is around four to six months, though this can be extended with new data.
Improper storage conditions can accelerate the degradation of these sensitive components. Exposure to extreme temperatures (too hot or too cold) or high humidity can compromise the test’s performance before its printed expiration date. For instance, leaving tests in a hot car or an unheated shed can make them unreliable because heat damages the chemicals and antibodies. To maintain accuracy, store tests within the manufacturer’s specified temperature range, typically below 86 degrees Fahrenheit.
Test Accuracy with Expired or Improperly Stored Kits
Using an expired or improperly stored COVID-19 rapid antigen test can compromise its accuracy. While false positives from expired tests are generally considered less common, they can occur due to non-specific binding of degraded reagents. However, if an expired test shows a positive result, it is likely a true positive, indicating the antibodies were still functional enough to detect the virus.
A more significant and common risk associated with expired or compromised tests is false negatives. When the antibodies or chemical reagents degrade, they may lose their ability to bind effectively with viral proteins, even if the virus is present. This means the test might fail to detect the infection, leading to a negative result when the individual is actually infected. Such a false negative can have implications for public health, as an infected person might unknowingly spread the virus.
Interpreting Potentially Compromised Results
Before using a rapid COVID-19 test, always check the expiration date printed on the box and verify the recommended storage conditions. The U.S. Food and Drug Administration (FDA) has extended expiration dates for many tests based on new stability data from manufacturers. You can check the FDA’s website to see if your specific test’s expiration date has been extended by looking up its lot number.
If you have used an expired or improperly stored test and receive a positive result, it is generally advised to confirm this with a new, unexpired test or a more sensitive laboratory-based PCR test. If an expired test yields a negative result, but you have symptoms consistent with COVID-19 or suspect exposure, retesting with an unexpired kit within 24 to 48 hours is a prudent step. This retesting helps to increase confidence in the result, especially given the higher likelihood of false negatives with compromised tests.