Beware the expired RAT

RATs being used past their expiry date add to the challenge of gathering accurate covid numbers.

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Infectious diseases experts and the Department of Health and Aged Care have warned against relying on expired rapid antigen tests as their accuracy can’t be guaranteed.

Anecdotally, many Australians still have the self-testing kits at home after millions of tests were given away towards the end of the pandemic, and the majority of these have passed their expiry date.

There were no guarantees that expired RATs were accurate, said infectious diseases physician and microbiologist Associate Professor Paul Griffin from the University of Queensland.

“We have no assurances on the accuracy of anything that’s past its use by date,” the director of infectious diseases at Mater Health Services told The Medical Republic.

RATs needed to be used “completely in accordance with the manufacturer instructions”, he said.

“As soon as you do anything that’s not specifically in complete accordance with the instructions that are included, the test result becomes essentially invalid, and that holds true for the expiry date as well,” said Professor Griffin.

“The wise thing to do is to get a new one.”

That was also the case for RATs that had been stored in high temperatures – such as in cars – as this could compromise their reliability, he said.

“Most people aren’t aware that RATs even have an expiry,” he said.

A spokesperson for the Department of Health and Aged Care said consumers were advised not to use RATs after their expiry date as the results may be inaccurate.

“Some manufacturers have continued their shelf life studies, following approval of the device with an agreed shelf life based on supporting data,” the spokesperson told The Medical Republic.

“These data can be submitted to the TGA to support extending the shelf life of the RAT beyond the initially approved shelf life.”

The TGA verifies the extended shelf-life data and publishes any approved shelf-life extensions.

The spokesperson said some batches of RATs supplied before the extended shelf life for that product was approved may be labelled with the original, shorter shelf life.

“Sponsors or distributors, with consent from the manufacturer, can relabel these devices with the extended expiry date,” said the spokesperson.

“Organisations with stock of RATs can contact their suppliers to confirm the expiry dates.”

The DoHAC spokesperson said anyone with covid symptoms should get tested as soon as symptoms develop, particularly if they were at higher risk of severe illness to allow early treatment with covid antiviral medications, if eligible.

“It is recommended that people who are eligible for covid-19 oral antiviral medication have a plan in place with their GP or nurse practitioner to enable access to covid-19 oral antiviral medication as soon as possible after a positive covid-19 test,” they said.

Isolating after a positive covid test is no longer legally required in any state or territory, and there is no requirement to report positive RATs.

The DoHAC spokesperson said states and territories were responsible for implementing public health measures.

Professor Griffin said RATs still had a role in covid detection but warned they could return false negatives.

“I think many people have lost sight of the right context in which to use them,” he said.

“If they’re positive, we can believe that result.”

But if people have covid but have no symptoms or few symptoms, the RAT can be unreliable, Professor Griffin said.

False negatives could lead to false reassurance and the further spread of covid if people think they “can do whatever they like” such as visit aged care facilities, he said.

Professor Griffin said RATs were far less sensitive than polymerase chain reaction (PCR) tests.

PCR-based testing was more difficult to access, he said, but it was extremely sensitive and far more reliable than rapid antigen testing, particularly for people in the early stages of infection or with few symptoms and a lower viral load.

There have been almost 22,500 covid notifications across Australia so far this year, figures from the National Notifiable Disease Surveillance System show (as of 18 January).

But many positive RATs were not reported, according to the Immunisation Coalition.

“The case numbers are extremely inaccurate, basically meaningless at the moment,” said Professor Griffin.

“That leaves us almost solely relying on hospitalisations, which is still a useful surrogate, but even at the moment it’s likely that the proportion of people being hospitalised is a lot less than it used to be.

“It is really hard to know just how much covid is out there.

“I’m not suggesting we return to using PCR testing sites, but encouraging PCR-based testing and making rapid antigen tests available and recording their results would still be helpful.”

Note: Since publication, copy has been updated to include information on isolation and reporting requirements.