source : www.abc.net.au
Okay, hands up – who has a stockpile of rapid COVID antigen tests in the cupboard?
Most important points:
There is wide variation in the accuracy of rapid COVID antigen tests
Experts say we still need RATs to stop the spread of COVID and ensure timely treatment
There is a lot you can do to maximize the accuracy of RATs
As COVID continues to make the rounds, you may find yourself reaching for one of those tests. But your RAT test may leave you puzzled as to whether or not you are infected with Sars-CoV-2 if it has passed its expiration date.
Even if the test is still current – and has been stored at the correct temperature – the result may still not be accurate.
While some of the blame for this lies with not using RATs correctly, a new study suggests that manufacturers have also overestimated the accuracy of their tests.
So what’s the story and what can be done to increase test accuracy?
In 2022, a Cochrane review found huge variation in ‘sensitivity’ – the ability to accurately pick up a positive case of COVID – between different brands of RATs.
“When tests were used according to manufacturer’s instructions, the average sensitivity per brand ranged from approximately 34 percent to 93 percent,” said Emily MacLean, an epidemiologist at the University of Sydney.
She said the accuracy of the RAT in the studies was generally confirmed using PCR.
Still, the World Health Organization recommends that RATs have a minimum sensitivity of 80 percent — meaning they pick up at least 80 out of 100 positive cases and miss 20.
“So some of those RATs (studied by Cochrane) certainly did not meet the WHO target sensitivity,” Dr MacLean said.
Dr. MacLean and colleagues decided to compare the accuracy estimates from the Cochrane review with manufacturers’ claims on the small pieces of paper – the ‘instructions for use’ – found in test kits.
To minimize the impact of ‘user error’, they only included research in which people who used the tests stated that they followed the manufacturer’s instructions.
The new study of 22 tests, published in Lancet Microbe, found that manufacturers claim accuracy has been overestimated by 12 percent on average, meaning 12 additional positive cases would be missed per 100 people infected.
“Not every test exaggerates sensitivity, but more of them do than not,” Dr. MacLean said.
Evaluation of real-world tests
While RATs are evaluated before they are sold, the 2022 Cochrane review looked at how the tests actually worked when they were deployed, Dr. MacLean said.
And this is when many factors can affect accuracy.
For example, RATs are known to have lower accuracy in people with few symptoms and in people who test too early after being infected.
And as mentioned, not following the test instructions can be a problem.
For example, if you eat, smoke, brush your teeth, or chew gum before performing a spit test, accuracy may be lost.
Touching the swab or forgetting to blow your nose before a nasal test can also cause problems.
“Some tests are more robust to user error than others,” said Dr. MacLean.
Paul Griffin, director of infectious diseases at Mater Health Services in Brisbane, said it was important to understand the limitations of RATs.
“The biggest limitation is sensitivity. There is a relatively high false negative rate, meaning it can miss COVID quite easily, especially if done early or incorrectly.”
Dr. Griffin said that given that the accuracy of tests is generally assessed in “ideal conditions,” it is not surprising that they have lower accuracy in the real world.
However, experts suggest that medical professionals and people who perform regular tests are more likely to get an accurate result.
‘Tests remain important’
Although most states no longer collect RAT results, Dr. Griffin said the tests still play an important role in controlling the spread of COVID, and ensuring that effective treatment is given early enough to work properly.
“We still currently have around 200 outbreaks of COVID in aged care facilities across the country,” he said.
“It is still very important that we find people with COVID, especially those who are at high risk.”
Dr. Griffin said access to oral antivirals was dependent on a positive test, and with PCR tests now much harder to obtain, this put more importance on rapid antigen tests.
“While there is very little public talk about it these days, COVID is still around and will be for the foreseeable future,” he said, adding that everyone should consider using RATs.
“It’s the right thing to do – isolate if you have COVID.”
His advice for maximizing the accuracy of your RAT is to use the Therapeutic Goods Administration list of approved COVID-19 rapid antigen tests to find a test with the highest sensitivity possible, and then be careful about how you perform the test.
“There are subtle differences in the way they all work, so you should make sure you follow the manufacturer’s instructions provided,” said Dr. Griffin.
He also says it’s worth getting a “combination test” that detects RSVs and types of flu.
Call for more transparency in test evaluation
Jon Deeks, professor of biostatistics at the University of Birmingham, who led the Cochrane review on RAT accuracy, and co-authored the new study with Dr MacLean, is calling for a major change when it comes to test evaluation.
He says there is a lack of transparency in manufacturers’ evaluations and relatively little evidence is used to evaluate tests compared to drugs.
“We’re back about 30 years in terms of the strength of the evidence we can get,” Professor Deeks said.
However, a spokesperson for the Therapeutic Goods Administration stated that the TGA’s expectations for manufacturers were in line with the requirements of the World Health Organization (WHO) and the European Commission, and no change was proposed.
The TGA conducts ongoing independent verification of approved RATs to ensure compliance with requirements.
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source : www.abc.net.au