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COVID-19 rapid antigen tests (RATs) have been widely used for diagnosis of COVID-19. The World Health Organization (WHO) COVID-19 Case Definition states that a person with a positive RAT (also known as an antigen rapid diagnostic test or Antigen-RDT) can be considered a "confirmed case of SARS-CoV-2 infection" in two ways. [10]
A COVID-19 Rapid Antigen test(top) with a Covid-19 Rapid Antigen and a Influenza A&B Rapid Antigen Test(bottom) A rapid antigen test (RAT), sometimes called a rapid antigen detection test (RADT), antigen rapid test (ART), or loosely just a rapid test, is a rapid diagnostic test suitable for point-of-care testing that directly detects the presence or absence of an antigen.
The antigen test checks for a protein on the virus and needs a certain amount of the virus to show a positive result. It typically turns negative within five to 14 days after infection."
In the most basic sense, there are four possible outcomes for a COVID-19 test, whether it’s molecular PCR or rapid antigen: true positive, true negative, false positive, and false negative.
A person may test positive because they are still shedding viable virus, or it could be viral debris that is being picked up by the test, says Amesh A. Adalja, M.D., senior scholar at the Johns ...
A rapid antigen test quickly searches for antigens, protein fragments that are found on the surface of or within a virus. Antigen tests can be analyzed within a few minutes. Antigen tests are less accurate than PCR tests. It has a low false positive rate, but a higher false negative rate.
Most people will stop testing positive on a rapid antigen COVID-19 test within about 10 days, Cardona says. "Within 10 days after your initial positive test, you should convert back to negative ...
If an antibody is already bound to an antigen, that antibody and that antigen cannot bind to the test. Antibody tests therefore cannot detect that specific antibody molecule. Due to this binding, if the amounts of antigen and antibody in the blood are equal, each antibody molecule will be in a complex and be undetectable by standard techniques.