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.
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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.
- Hassan Vally is an associate professor in epidemiology at Deakin University
- Correction: A recent column that mentioned the Adani coal mine referred to groundwater usage as 12,000 megalitres per day. The correct source of the water is floodwater from the Suttor River, and the correct value is approval to purchase up to 12,500 megalitres per year. Groundwater will be extracted from local aquifers within the coal seams, not from the Great Artesian Basin.
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