How to take a RAT test and try to avoid false negative results

Who is to blame for RAT test false negatives - manufacturers or the people using them? Here's how you should be taking a RAT.

While PCR tests are still available and remain the "gold standard" for testing, many have turned to rapid antigen tests (RATs) out of convenience or as part of a requirement to return to work or school.

In New Zealand, RAT tests are now the first port of call for anyone who wants to ascertain whether or not they have Covid-19. In June, Covid-19 Response Minister Dr Ayesha Verrall said although PCR was not the primary test at the moment, the New Zealand government was ensuring it retained PCR capacity, and would retain contact-tracing networks.

RAT tests can provide results within minutes, do not require a healthcare worker or lab to process, and help to catch Covid-19 cases that otherwise would have gone undetected.

But with these benefits come a range of limitations: the biggest one being that they can provide false negative or false positive results.

Recently, some Australian doctors have warned people against relying on a negative RAT result.

Meanwhile, the makers of RATs have hit back, blaming false negatives on a lack of education about how and when to properly use the tests.

So is there any evidence that indicates the effectiveness of RATs has been impacted? And does it have to do with people using them incorrectly?

Australians face 'education gap' over using RATS

Pathology Technology Australia, the peak body for test manufacturers and suppliers, defended the performance of rapid tests against new variants of Omicron, accusing critics of "fearmongering".

"Nothing has changed, we're yet to see any evidence that clearly indicates performance has been impacted by the subvariants," chief executive and clinical biochemist Dean Whiting said in a statement.

"There is an education gap in Australia that was never filled after RATs became available."

"I think a lot of the false negative results are due to incorrectly collecting the sample," Whiting said.

Here are the essentials when taking a RAT:

Store the test at 2C-30C

The Therapeutic Goods Administration (TGA) warns that tests "may not work properly" if they have been exposed to excessive light or heat, or if the packaging is damaged.

The instructions for a RAT specifically say to store it in a cool, dry place at 2 degrees Celsius up to 30C.

Do not freeze the kit and do not store it in direct sunlight.

Check the expiration date

According to the TGA, RATs can be stored for 12 months from the date of manufacture.

Do not use the test after its expiration date.

Blow your nose

David Speers, a clinical microbiologist and head of the microbiology department at PathWest, told ABC Radio Perth this would clear any excess mucous so that it would not interfere with the results.

"What you want to do is sample the lining of the nose - you're not sampling the secretions as such," he said.

Only open the kit right before use

If you open the kit components, don't suddenly delay taking the test and leave it out until you decide to.

When you open the kit, take the test straight away.

Don't contaminate the test

Whether it is with your fingers or your kitchen tiles after dropping it (there's no five-second rule here), the tip of the swab should not touch anything.

So make sure it doesn't come into contact with any other surfaces.

Swabbing at the wrong angle and depth

You've made it to the hardest part.

It's easy for many to get the angle or depth wrong when it comes to swabbing.

Whiting said he had seen many people wave the swab around the inside of their nostrils when taking a RAT.

"This is not the way the manufacturer intended for you to use the test," he said.

"The manufacturer intended you to put the swab at least 1.5cm up your nose and swish it around five times, then do the other side."

A guide published by the Public Health Laboratory Network (PHLN) and the Department of Health says to insert the swab tip 2cm to 3cm into each nostril. New Zealand's Ministry of Health has also issued instructions on how to use a rapid antigen test.

The key is to insert the swab all the way up your nostril until you feel it rub against the back of your nose.

• RAT tip: You're not swabbing the inside of your nostril. You're swabbing the tissue further back in the nasal passages.

Rather than going directly upwards with the swab, make sure the swab passes horizontally.

Then rotate the swab gently against the walls of the nasal passage five times, for 15 seconds in each nostril.

"You will know when you're doing this correctly because it's slightly uncomfortable," Whiting said.

"If your eyes aren't watering or you're not resisting the urge to sneeze, then you're not taking the sample correctly."

Swirl the swab in the tube for 10 seconds

Hold the solution tube firmly with one hand.

Once you've inserted the swab into the tube, swirl it around in the fluid for 10 seconds.

Then pinch the swab tip through the tube to remove any remaining fluid.

For some testing kits, you will need to snap the end of the swab. The swab will indicate where to do this.

Don't add too many drops to the device

Remove the test device from its protective package and place it on a well-lit, flat surface.

Keep the tube vertical with the cap pointed down.

Squeeze three drops of liquid from the tube into the well on the device.

Some tests say two drops, while others may say four. Make sure you follow the instructions of the manufacturer of your test.

Adding too many drops or too few will affect the timeline and the test will be inaccurate.

• RAT tip: If clogging occurs, gently tap the bottom of the tube to release the blockage.

Follow the 'no earlier than 15, no later than 20' rule

Keep the test device on a flat surface.

Read the result at 15 minutes.

Do not read it earlier than this, or after 20 minutes.

After 20 minutes, the result might become inaccurate.

• RAT tip: A Control (C) line may appear in the result window within a few minutes but a Test (T) line may take as long as 15 minutes to appear.

Misreading the result

• Two lines mean you have tested positive for Covid-19
• A line at C only means you have tested negative for Covid-19
• A line at T but not C means your test is faulty
• No lines means your test is faulty

Dispose of the kit correctly

Make sure you place the swab, tube and test device into the plastic bag provided and seal everything in there.

Then you can dispose of it in the rubbish bin.

As more variants emerge and evolve over the pandemic, many are wondering whether we're likely to get a variant that can elude testing.

Epidemiologist and biostatistician from the University of South Australia Adrian Esterman said at some point in time, we would likely get a variant that was much harder to detect with existing tests.

But because of Australia's diverse population and geographical spread, Whiting believes RATs are going to remain highly useful, especially in rural and remote areas.

NZers, report your results

New Zealand's Ministry of Health asks that you report the result of your RAT test whether positive or negative at mycovidrecord.health.nz or call 0800 222 478 and press option 3.

The New Zealand government recently removed eligibility criteria for getting access to free rapid antigen tests. People are longer be required to say they have symptoms to get access to free RATs through the request a RAT website.

- ABC / RNZ