Rapid COVID-19 antigen tests have become a widely used tool for quick self-assessment of SARS-CoV-2 infection. Understanding how to correctly interpret these tests is important for personal health decisions and to help limit community spread. These at-home tests offer a convenient way to determine infection status, providing results within minutes.
Components of a Rapid Test
A standard rapid antigen test kit includes a test cassette containing a nitrocellulose test strip. This strip features two distinct lines: the Control (C) line and the Test (T) line. The Control line serves as an internal check, confirming that the test has functioned correctly and enough sample has flowed through the device. The Test line is where SARS-CoV-2 antigens, if present in the sample, bind to specific antibodies, indicating a positive result.
When a sample is applied to the test cassette, it travels along the strip through capillary action. If SARS-CoV-2 antigens are present, they interact with labeled antibodies and become visible at the Test line. The Control line will always appear if the test process is valid.
Deciphering Your Test Lines
Interpret rapid COVID-19 test results by observing the presence and location of lines on the test cassette within the manufacturer’s specified timeframe (usually 15-30 minutes).
A positive result is indicated by the appearance of two lines: one at the Control (C) region and another at the Test (T) region. Even a very faint line at the Test (T) region indicates a positive result.
A negative result is shown by the presence of only one colored line, appearing solely at the Control (C) region, with no line visible at the Test (T) region.
An invalid result occurs if no line appears at the Control (C) region, or if no lines appear at all.
Next Steps After Testing
If a test shows a positive result, you likely have COVID-19. Isolate at home for at least five days from the onset of symptoms or the date of the positive test if asymptomatic. Inform close contacts and monitor symptoms, seeking medical advice if they worsen.
If a test yields a negative result, it suggests that the virus was not detected at the time of testing, but it does not completely rule out an infection. It is advisable to continue practicing public health precautions, such as mask-wearing, and consider retesting at least 48 hours later, especially if symptoms persist or if there was known exposure.
For an invalid result, where the control line did not appear, the test should be considered inconclusive. In this instance, it is necessary to retest immediately using a new kit and carefully following all instructions to ensure accuracy.
Common Reasons for Unclear Results
Several factors can lead to an unclear or invalid result on a rapid COVID-19 test. One common reason is improper sample collection, such as not swabbing adequately to gather enough viral material. Incorrect application of the buffer solution, including using too little or too much, can also prevent the test from running correctly.
Reading the test result outside the specified time window, either too early or too late, can also lead to misinterpretation. The test should be read within the timeframe indicated in the instructions, typically 15-30 minutes, as results may become inaccurate if left for too long. Additionally, using an expired test kit or one that has been stored improperly can compromise the integrity of the test components, leading to unreliable outcomes.