Schoolchildren have discovered that applying orange juice to a Covid lateral flow test can generate a fake “positive” result.
The phenomenon – which has been verified through an experiment by the Guardian – is not a result of the juice containing the virus. Rather it appears to be linked to its acidity, which essentially breaks the test. The effect has allegedly also been seen with a number of other foods and drinks including ketchup and Coca-Cola.
One UK science teacher said they were shown the orange juice effect by their students. “They say it’s a great way to get two weeks off school,” they said.
Prof Andrea Sella of University College London said the discovery was not surprising. “If someone deliberately mucks up the protocol then of course you’ll get a duff result. But I would add that it’s not a ‘false positive’ in the true sense. Because false positives are ones that take place in spite of adherence to the protocol.”
The “trick” has also been featured on TikTok, with videos of people trying out different fluids. According to the i newspaper, there have been more than 6.5m views of videos uploaded to the social media platform under the search term #fakecovidtest.
Jon Deeks, a professor of biostatistics at the University of Birmingham, criticised the practice. “False positives affect not just that child but their family and their bubble at school, so [it is a] pretty selfish thing to do. There are less harmful ways to fake a day off school,” he said.
Writing in the Conversation, Mark Lorch, a professor of science communication and chemistry at the University of Hull, said it was possible to spot a “faked” positive test by washing it with a buffer solution that restores the correct pH to the device. After this process the “positive” line in a faked test disappears, revealing the negative result.
While the faking of positive lateral flow tests may cause concern, not least because everyone in a household must self-isolate immediately should a test show a positive result, the disruption may be short-lived: anyone with a positive test must subsequently take a more accurate PCR test to confirm an infection.
Geoff Barton, the general secretary of the Association of School and College Leaders, said: “Misusing lateral flow tests in any way is massively unhelpful and we would strongly discourage this behaviour. We are sure this involves a very small minority of pupils, and that for the most part the tests are used correctly.
“However, we would urge parents to ensure that tests are not being misused, and we would suggest to pupils who are interested in chemical reactions that the best place to learn about them is in chemistry lessons in school.”
This content was originally published here.