At-home COVID-19 tests offer a convenient way to quickly assess potential infection, providing results within minutes. Knowing how to accurately interpret these results is important for making informed decisions about your health and the well-being of those around you. This guide clarifies the process of reading your at-home COVID-19 test.
Understanding Rapid Antigen Tests
Rapid antigen tests detect specific proteins from the SARS-CoV-2 virus. These tests differ from PCR tests, which look for the virus’s genetic material and are typically processed in a laboratory. Rapid antigen tests are quicker, providing results in about 15 to 30 minutes, making them useful for identifying active infections, especially when viral load is high.
A typical rapid antigen test kit includes a collection swab, a solution, and a test cassette. After collecting a sample from the nose, the swab is mixed with the solution. This mixture is then applied to the test cassette, which contains a strip with two distinct lines: the Control (C) line and the Test (T) line. The C line confirms the test functioned correctly and that enough sample was applied. The T line detects the presence of viral proteins; if these proteins are present in the sample, a line will appear at the T position.
Interpreting Your Test Results
Interpreting rapid antigen test results involves observing the C and T lines within a specific timeframe, typically 15 to 30 minutes after applying the sample. It is important not to interpret results after this recommended window, as doing so can lead to inaccurate readings, including false positives or negatives.
A positive result is indicated by the appearance of two colored lines: one at the Control (C) and another at the Test (T) line. Even if the line at the T position is very faint, it still signifies a positive result, indicating the detection of viral antigens. The intensity of the T line does not change the result itself, though a fainter line might suggest a lower viral load or that the infection is either just beginning or nearing its end.
A negative result is shown when only the Control (C) line appears, with no line visible at the Test (T) position. This indicates that SARS-CoV-2 antigens were not detected in the sample. However, a negative result does not completely rule out an infection, particularly if symptoms are present, as rapid antigen tests are less sensitive than molecular tests like PCR.
An invalid result occurs if the Control (C) line does not appear, regardless of whether a line is present at the Test (T) position. This means the test did not function properly. Common reasons for an invalid result include incorrect sample collection, insufficient solution, using an expired test, sample contamination, or improper storage temperatures.
What to Do After Testing
If your test result is positive, you likely have COVID-19. It is advised to isolate immediately to prevent further spread of the virus, typically for at least 5 full days from the day symptoms began or the positive test was taken if asymptomatic. Informing close contacts about your positive status is also recommended so they can monitor for symptoms and get tested if needed. If symptoms worsen or become severe, such as difficulty breathing, medical attention should be sought promptly.
If your test result is negative, it suggests you may not have COVID-19, but it does not completely rule out an infection. Continued vigilance is important, especially if you have symptoms or have been exposed to someone with COVID-19. The FDA recommends repeat testing 48 hours after a negative result, and potentially a third test 48 hours after the second negative, especially if symptoms persist or you were exposed without symptoms. You should continue to practice public health precautions, such as masking in crowded indoor settings and frequent handwashing.
If your test yields an invalid result, it means the test did not work correctly. Retest using a new, unexpired kit, carefully following all instructions provided by the manufacturer. If symptoms continue or concerns persist after an invalid test, consulting a healthcare provider for further guidance or to consider a more sensitive laboratory-based test, such as a PCR test, is advisable.