Lateral flow tests might not be able to detect asymptomatic carriers

Updated on April 27, 2021 at 4:02 PM

Tested negative with a lateral flow device? Here’s why you still need to exercise caution when you’re going out!

The British government has been relying heavily on using Innova lateral flow tests (LFT) to mass test the population for COVID and currently, a majority of COVID tests are being done through LFTs. This device has allowed hundreds of thousands of citizens to rapidly test themselves at home. To get your results, you have to take a swab from the back of your nose, or throat, and put the swab in the tube of liquid that is provided. Then, you squeeze the liquid into the device, and in 30 minutes you will know whether or not you are COVID positive or negative.

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Testing asymptomatic carriers

Although the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) did authorise the use of these tests, they have become concerned over the way that it is being used.

The MHRA approved lateral flow testing, under the circumstances that it was to be used as a ‘red light’ test—identifying who is positive, and keeping them isolated. Not a 'green light' test that allows people who are negative to exercise certain freedoms. This is because the test is significantly more accurate when recognising COVID-positive cases with high viral load. Unfortunately, its accuracy begins to decrease when testing people who are asymptomatic. A Cochrane review found that accuracy dropped to 58% when testing asymptomatic carriers.

False negative results

What experts are concerned about is that people who do get false negative results will start to be less careful, especially when it comes to following safety guidelines. Susan Michie, from the Sage subcommittee advising on behavioural science, told The Guardian:

There is a real concern that if people use lateral flow tests as a confirmatory test then they may be counterproductive as people may be less careful with their behaviour than if they had not taken the test at all.

The Guardian has reported that the MHRA is asking the government to provide sufficient evidence to prove the accuracy of the test, and to educate the public about the benefits and the risks of mass testing with LFTs.