Rapid antigen COVID-19 tests offer a quick way to check for the virus at home, providing results within 15 to 30 minutes. Understanding the lines on these tests is important for interpreting results and taking appropriate next steps. These visual cues indicate if the test functioned correctly and if viral proteins were detected.
Understanding the Control Line
The ‘C’ on a rapid antigen test signifies the Control line. This line confirms the test kit is functioning correctly, indicating the sample moved properly and reagents are active. The Control line must always appear, regardless of virus detection, to ensure test validity. If it doesn’t become visible, the result is invalid and cannot be trusted. This can occur if the sample was applied incorrectly, the test expired, or was stored improperly.
Interpreting Test Results
Interpreting rapid antigen test results requires observing both the Control (‘C’) line and the Test (‘T’) line. The ‘T’ line appears when specific viral antigens from the SARS-CoV-2 virus are detected in the sample. These antigens serve as an early indicator of infection.
A valid negative result occurs when the ‘C’ line is present, but no ‘T’ line appears. This indicates that the test worked, but no SARS-CoV-2 antigens were detected at a level the test could register. It is important to note that a negative antigen test does not completely rule out an infection, especially early in the infection or if symptoms are absent, as these tests are less sensitive than laboratory-based PCR tests.
A valid positive result shows both the ‘C’ and ‘T’ lines. Even a faint ‘T’ line indicates a positive result, meaning viral antigens were detected. This suggests an active COVID-19 infection, and the individual is likely contagious. Any visible ‘T’ line signifies a positive outcome, regardless of its intensity.
An invalid result occurs if the ‘C’ line does not appear, even if a ‘T’ line is present. This means the test did not perform as intended, and the result cannot be relied upon. In such cases, discard the test and perform a new one with a fresh kit, carefully following all instructions.
Next Steps After Testing
After obtaining a rapid antigen test result, specific actions are recommended. If positive, it is highly probable the individual has COVID-19. Isolate immediately to prevent further spread, following public health guidelines. Also, monitor symptoms and contact a healthcare provider for guidance or if symptoms worsen.
For a negative test result, especially if symptoms are present or there has been a known exposure, caution is still necessary. Rapid antigen tests can sometimes miss early infections or detect lower viral loads. Public health recommendations often suggest repeat testing 48 hours after an initial negative result, particularly if symptoms persist or if there was an exposure. If symptoms continue to worsen despite negative antigen tests, consulting a healthcare professional for a more sensitive PCR test or to investigate other potential illnesses is advisable.
If an invalid result occurs, the immediate next step is to retest using a brand new test kit. It is important to carefully review and follow the manufacturer’s instructions for sample collection and test execution to avoid another invalid result. If symptoms persist after an invalid test, seeking advice from a healthcare professional is important, as they may recommend a laboratory-based molecular test for a more definitive diagnosis.