As a new COVID wave moves across the country, many Australians are rifling through medicine cabinets in search of rapid antigen tests (RATs) at the first sign of a cough.
It’s a wise precaution, but is that test you’ve had for months still effective? Probably, but there’s one important factor you need to consider – temperature.
The Therapeutic Goods Administration (TGA) is conducting a post-market review of the tests, but anyone with kits stored at home should follow some basic guidelines before using them.
Checking the expiry date is not a bad starting point, but it won’t give you the full story.
There are two reasons for that. One, many RATs manufactured in the earlier days of the pandemic were labelled with expiry/expiration dates of four to six months from production. But with the collection of longer-term data, these timeframes have been extended to 12 months and beyond.
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Graham Gordon, CEO of Gardian, the Australian supplier of GardianT3 Covid-19’ rapid antigen tests, explains the change. “GardianT3 Covid-19 rapid antigen tests were extended to 18 months, based on clinical and analytical evidence,” he says. “The Therapeutic Goods Administration assessed the efficacy of GardianT3 saliva-based tests via post market research and concluded the expiry date of GardianT3’s had an extended shelf life of 18 months.”
That sounds quite straightforward, but Mr Gordon adds a cautionary note. “Simply checking the expiry date of your rapid antigen tests is not enough. There are other factors such as how the tests have been stored that need to be taken into account.”
The most important of those factors, he says, is storage temperature. “If tests are not stored at the correct temperature of 2°C to 30°C, this can render the test unusable. The test could display a false negative or invalid test result.”
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Importantly, this includes temperatures that are too cold, as well as too hot.
“If the test is exposed to very hot or cold temperatures,” says Mr Gordon, “it will degrade faster than if it’s kept at more stable temperatures. Test performance may also be impacted if the test is used in outdoor temperatures below freezing. At high altitude or in the middle of winter for example, or in a very hot or humid environment, such as the harsh Australian summer.”
Mr Gordon extends that warning to those who may have moved house and had RATs placed in storage units, even temporarily. “You may think that storing tests in a storage unit is safe, but unless air conditioned or temperature controlled, you may find that these tests are now unusable,” he says.
Why is the storage temperature so important?
There are two main reasons for this. The first is that the test strip that forms part of each RAT is coated with antibodies that will change colour when they come into contract with nucleocapsid protein – one of the most abundant markers of COVID. These antibodies are very sensitive and prone to damage if exposed to extreme temperatures.
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Likewise, the test solution also contains chemicals that could be influenced by extreme temperatures.
If your RATs have been stored in a space that hasn’t been exposed to temperatures outside the 2°C to 30°C range and within the recommended use period, they should still be effective. But if you are unsure in any way, Mr Gordon recommends invoking the old adage: ‘If in doubt, throw it out.’
Do you have rapid antigen tests at home? Are you sure they’ve been stored within the correct temperature range? Why not share your experience and thoughts in the comments section below?
