A rapid antigen test (RAT) is a chemical test that detects the presence of the COVID virus in the body. It's effectively a portable chemistry laboratory on a strip of plastic that detects viral proteins in a sample of nasal secretions or saliva.
Present within the RAT are antibodies that are able to bind to specific parts of the SARS-CoV-2 virus (called epitopes). If a nasal or salivary sample collected contains viral particles, these then attach to the antibodies through these epitopes.
When this occurs, the antibodies, which also have a fluorescent marker attached to them, are able to attach to other antibodies that are affixed on the surface of the RAT test. They then light up and indicate a positive result.
A key difference between a RAT and the gold-standard polymerase chain reaction (PCR) test is that while a RAT tests directly for viral particles, a PCR tests for the presence of viral genetic material.
The key advantages of a RAT are that it is much cheaper and quicker than the PCR test. Instead of queuing at a testing centre, it is possible for testing can be completed outside a health care setting and you get the result in about 15 minutes.
The disadvantage, however, is that RATs have a lower accuracy than PCR tests. However, it's important to note that any RAT approved for use in Australia must meet certain standards of accuracy.
This includes being required to have a sensitivity (how well a test detects COVID-19) of at least 80 per cent and a specificity (how well a test can confirm the absence of COVID-19) of at least 98 per cent.
While not perfect, this level of performance makes RATs excellent as screening tests.
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