Applying fruit juice to a lateral flow test breaks the lateral flow test. Lateral flow tests play an important role in the fight against COVID-19.
Lateral flow tests (LFTs) are one of two common types of COVID-19 test, the other being polymerase chain reaction (PCR) tests. As the BBC has explained, lateral flow tests and PCR tests do different things: "LFTs pick up the most infectious people by detecting material from the surface proteins of the virus PCRs detect genetic material of the virus which can be present in the body for several weeks after somebody is actually capable of passing it on [...] LFTs can be done at home, and show results in 20-30 minutes. PCR test swabs must be sent to a lab for analysis, with results provided in 24-48 hours."
In July 2021, the Guardian wrote about why applying fruit juice to a lateral flow test can trigger a positive result, saying, "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."
A Reuters fact check echoes this. Quoting Professor Mark Lorch of the University of Hull, the Reuters article explains that "the beverages and other solutions used do not contain the COVID virus," adding that it is the acidity that "disrupt(s) the delicate antibodies on the test devices and so corrupt(s) the test results."
According to an article in the FT, "rapid lateral flow tests have always been imperfect, detecting an average of 72 per cent of symptomatic cases, and 58 per cent of asymptomatic ones." The same article, however, states that "repeating tests can make the results more robust, so many experts endorse the government recommendation for vaccinated people exposed to the virus to test for seven days straight."
However, Irene Petersen, a professor of epidemiology at University College London, spoke to Bloomberg about lateral flow tests, saying, "It's very likely you have Covid if you get a positive lateral flow test." Furthermore, in October 2021, a study found that "lateral flow tests are more accurate than previously reported and cannot be compared directly to how PCR tests work."
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19, including symptoms, prevention, and available treatment, please refer to the World Health Organization or your national healthcare authority.