Rapid antigen COVID-19 tests are a common tool for quickly assessing potential infection status. These tests detect specific viral proteins, known as antigens, providing results within 15 to 30 minutes. Understanding how to use and interpret these at-home test kits is important for informed health decisions and preventing further spread.
The Control Line’s Function
The “C” line on a rapid COVID-19 test stands for “Control” and confirms the test’s validity. This line is designed to appear regardless of whether viral antigens are present in the sample, acting as an internal procedural check. Its appearance confirms correct test performance, sufficient sample application, and proper reagent function.
The control line contains specific antibodies that bind to components of the test solution, ensuring that the liquid has flowed properly across the test strip through a process called capillary action. If the control line does not appear within the specified timeframe, the test result is invalid. In such cases, discard the test and use a new kit to obtain a reliable result.
Reading Your COVID Test Results
Interpreting the results of a rapid COVID-19 test involves observing both the “C” (Control) line and the “T” (Test) line. The “T” line indicates the presence of SARS-CoV-2 viral antigens. If the “T” line appears, it suggests that viral antigens have been detected in the sample.
A valid negative result is indicated by the presence of a colored line only at the “C” position, with no line appearing at the “T” position. This outcome suggests that the test worked correctly, but no viral antigens were detected. For a valid positive result, both the “C” line and the “T” line must appear. Even a very faint “T” line, regardless of its intensity, should be interpreted as a positive result. An invalid result occurs if the “C” line is absent, regardless of whether a “T” line is visible. This signifies a test malfunction, and the result cannot be trusted.
Next Steps After Testing
Taking appropriate action after interpreting your rapid COVID-19 test result is important. If you receive a positive result, you are likely contagious. It is advised to isolate yourself at home and avoid contact with other people for a period, typically 5 days if you are 18 or older, or 3 days if under 18, from the day you took the test. Informing close contacts and considering a consultation with a healthcare professional, especially if symptoms worsen, is also recommended.
If your test result is negative, it means the test did not detect the virus, but it does not completely rule out an infection, especially if you have symptoms or were exposed. Continued vigilance, including mask-wearing and re-testing, is advised. The FDA recommends retesting 48 hours after a negative result. For an invalid result, discard the faulty test and retest immediately with a new, unexpired kit, following manufacturer’s instructions.