Rapid antigen tests (RATs) have found their way into homes across the country, allowing us to test for COVID-19 and get the results minutes later.
They’re easy to use and help expand the capacity of labs that process PCR tests, especially when they're under pressure to produce results quickly.
While RATs are recognised to be less accurate than PCR tests, there are some steps you can take to make sure you get an accurate result when testing at home.
When should I take a RAT?
You should take a RAT when you have symptoms of COVID-19 — fever, cough or losing your sense of taste or smell — according to Associate Professor Meru Sheel, an epidemiologist from the University of Sydney.
"That’s to do with the ability to detect the viral antigen. The more viral antigen you have, the greater ability you have to [end up with] a positive rapid antigen test."
"That doesn’t mean that an asymptomatic person may not test positive with a RAT, but the effectiveness is better for symptomatic people."
Most people develop symptoms five to six days after being in contact with a person who has active COVID-19.
Preliminary research suggests cases can be infectious for two to three days before a RAT is able to detect the virus — SARS-CoV-2 — so waiting a couple of days before you test isn't a bad idea if you're isolating anyway.
However, it's not entirely necessary to wait for symptoms to appear if you've had a known exposure, Dr Sheel suggests.
RATs can detect COVID-19 in asymptomatic people, however, it's useful to remember that the higher the viral load, the better the test will work.
How do I know my test is effective?
Australia's national drug regulator, the Therapeutic Goods Administration (TGA) has approved 47 different RATs for home use in Australia.
Of the 47 tests, they have been categorised into three sensitivity levels. These include:
- acceptable sensitivity (clinical sensitivity greater than 80 per cent) — five tests available
- high sensitivity (clinical sensitivity above 90 per cent) — 10 tests available
- very high sensitivity (clinical sensitivity above 95 per cent) — 32 tests available.
All of the TGA-approved tests need to have a clinical sensitivity of at least 80 per cent and clinical specificity of at least 98 per cent.
Higher sensitivity means there's less chance of a false negative result, while high specificity means there will be a lower rate of a false positive.
As the specificity rate is at 98 per cent, it's not very common at all to get a false positive result from a RAT.
If you buy tests online from overseas it's best to check that the RATs are approved by the TGA so that you know they provide an accurate result.
Could I have a variant that RATs don't detect?
It's highly unlikely.
Even though our population immunity has changed, due to high vaccination rates and the number of people who have now had COVID-19, Dr Sheel says the tests can still detect the different strains of the virus.
Can a RAT detect if I have a different winter virus?
Not yet, but Dr Sheel says health professionals may soon have to start testing for multiple different pathogens as other respiratory illnesses such as influenza and rhinovirus start circulating this winter.
"There’s a lot of viruses circulating. I think we’ll learn more in the coming weeks and expect some more guidance around what that looks like."
Dr Sheel says multiple pathogen testing has been done in previous winters, but this will look different now that COVID-19 is in the picture.
If you do have symptoms, no matter whether you think it's the common cold or not, you should isolate and take a RAT or PCR test.
Is there anything I shouldn't do before taking a RAT?
There are specific rules when you're taking a RAT test to make sure you get an accurate result.
The TGA says that, if you're going to take a saliva RAT, there's a number of things you can't do for up to 30 minutes beforehand, these include:
- eating
- drinking
- smoking or vaping
- brushing your teeth
- chewing gum.
With more brands of RAT tests expected to be sold in Australia, Dr Sheel says the most important thing you can do is read the instructions in the box and follow them properly.
Each RAT test may have slightly different rules to a different brand.
The tests also expire, many within 12 months, so if you've had some in your cupboard for a while, check the expiry date before you start.
What do I do if I test positive on a RAT?
If you test positive on a RAT, you must immediately isolate and register your positive result to your state or territory health department.
The rules for a positive case vary depending on where you live. Here's where you can find out exactly what you need to do:
- Australian Capital Territory
- New South Wales
- Northern Territory
- Queensland
- South Australia
- Tasmania
- Victoria
- Western Australia
Registering your result gives you access to support from health care services while you're in isolation.
Most governments require you to self-isolate for seven days and tell your household contacts that you've tested positive.
When should I get a PCR test?
RATs are a great way to get a quick indication of whether you've been exposed to COVID-19, but PCR tests produce the most reliable results.
If you suspect you have COVID-19 because you've been exposed, or you have symptoms but keep testing negative on a RAT, a PCR test can give you a more accurate result, Dr Sheel says.
A PCR test can detect COVID-19 before you're infectious, while a RAT can only detect when you're already infectious.
