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Covid: Lateral flow tests more accurate than first thought, study finds - BBC News
Oct 14, 2021 1 min, 58 secs

Lateral flow tests (LFTs) are very good at detecting people most likely to spread Covid-19 and positive results should be trusted, say University College London researchers.

Based on the UCL research, Prof Irene Petersen, lead study author, said people who get a positive LFT result "should trust them and stay at home".

But government guidance says people must get a follow-up PCR test after a positive LFT to confirm they have Covid - and they can end their self-isolation when they get a negative result in a PCR test.

The UK's Health Security Agency said it was looking into the cause, but there was no evidence of any technical issues with test kits.

Prof Petersen said: "When [Covid is] more common, there is no need to confirm it with a PCR - it's more likely it is a positive," she said.

When the researchers used a new formula for calculating the rapid test's accuracy, they found LFTs were more than 80% effective at detecting any level of Covid-19 infection and likely to be more than 90% effective at detecting who is most infectious when they use the test.

"It is most likely that if someone's LFT is negative but their PCR is positive, then this is because they are not at peak transmissible stage," he said.

The rapid tests are widely used in schools, workplaces and for allowing entry to large events to test those with no symptoms.

Since they were introduced in secondary schools in England in March, NHS Test and Trace figures show 103,409 LFT tests have come back positive, 79,000 were matched with a confirmatory PCR and 69,500 of those were confirmed positive (and 7,647 came back negative).

The current government guidance says that if you receive a negative follow-up PCR test result, and this PCR test was taken within two days of the positive LFT, you will be told by NHS Test and Trace that you can stop self-isolating?

However, it states that you must continue to self-isolate if the PCR result is positive, you choose not to take a follow-up PCR or the test was taken more than two days after the positive LFT?

Dr Sophia Makki, incident director for Covid-19 at the UK Health Security Agency, said: "Around one in three people who have Covid-19 never show any symptoms.

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