Rapid COVID-19 Antigen Test Results: How Do I Interpret Them?
The COVID-19 Antigen Rapid Test is a rapid membrane-based lateral flow immunoassay for the qualitative detection of SARS-CoV-2 antigens in human nasopharyngeal swab specimens. Using a rapid COVID-19 antigen test allows you to detect the presence of SARS-CoV-2 virus antigens in your body and take initial preventive isolation measures to reduce the further spread of the virus. These tests are particularly useful in identifying a person who is at or near the peak of infection. So the question is, how do I interpret the rapid antigen test result?
Structure of COVID-19 Antigen Rapid Test Cassette
The COVID-19 Antigen Test Cassette is coated with two lines (control line and test line). If the sample contains SARS-CoV-2 antigens, they will bind to the SARS-CoV-2 antibodies coated on the test line region (T) and generate a coloured line on the test strip, indicating a positive result. If antigens are not present in the sample, no coloured line will appear in the test line region (T), indicating a negative result. As a procedural control, a coloured line will always appear in the control line region (C), indicating that the test procedure was successful and the test components performed as expected.
Valid Rapid Antigen Test Results
- Positive Result: Two coloured lines appear.
One coloured line should always appear in the Control (C) region and another line should be in the Test (T) region. A positive result indicates the detection of SARS-CoV-2 antigens in the sample. A positive antigen test result is considered accurate when instructions are followed carefully, but there is a higher chance of false-negative results, meaning it is possible to be infected with the virus but still get a negative result.
- Negative result: a coloured line appears in the control region (C). No line appears in the test region (T).
As with the positive result, a coloured line must always appear in the Control region (C) for the test to be valid. A negative result indicates that the detection threshold for SARS-CoV-2 antigens in the sample has not been reached. The possibility of infection still exists if the concentration of antigens in the sample is too low to be detected by the rapid antigen test.
- Invalid Result: Control line does not appear.
Insufficient diluent volume or incorrect procedural techniques are the most likely reasons for the absence of the control line. Review the procedure and repeat the test with a new device. Antigen tests are relatively inexpensive and most can be used at the point of care. Most currently licensed tests to return results in approximately 15 minutes.
Antigen tests for SARS-CoV-2 are generally less sensitive than real-time reverse transcription-polymerase chain reaction (RT-PCR) and other nucleic acid amplification tests (NAATs) for the presence of acid. viral nucleic. However, RT-PCR can detect levels of viral nucleic acid that cannot be cultured, suggesting that the presence of viral nucleic acid does not always indicate infectivity.
Note: Please interpret the result of the rapid antigen and antibody tests within 15 to 30 minutes. The result is invalid if you check again in a few hours.