Lateral flow tests 95% effective at detecting Covid at start of symptoms

LFTs and PCR tests have ‘very similar’ accuracy in spotting Covid when symptoms start, a new study shows

Earlier studies had suggested that lateral flow tests (pictured) may be less sensitive than PCR tests (PA)

Lateral flow tests (LFT) are 95 per cent effective at detecting Covid-19 if used at the onset of infection and soon after symptoms start, according to a new study.

The tests return on-the-spot results in less than 30 minutes. LFTs have been made free on the NHS since April, but the government has not yet guaranteed that they will continue to be available free-of-charge past the end of July.

PCR, polymerase chain reaction, tests cost up to £200 each and are required to prove that someone is “fit to fly” abroad. The tests supplied by private companies are sent to labs and take up to three days to return a result.

Earlier studies suggested LFTs may be less sensitive than PCR tests in detecting Covid-19, researchers said.

But a new study – that is the first to compare two forms of testing on the same group of people on a large scale – has shown that LFTs and PCR tests have “very similar levels of accuracy” in spotting Covid, but only when symptoms first start.

More than 2,500 people with mild to moderate flu-like symptoms were assessed by GP doctors in Liezen, Austria.

It was part of a study carried out between 22 October and 30 November last year by the Queen Mary University of London, the University of Oxford, the Institute for Advanced Studies based in Vienna, and the Medical University of Graz.

They were tested for viral antigen using LFTs and those suspected to have Covid-19 also took PCR tests.

The LFTs detected more than 95 per cent of the cases found by PCR tests and correctly identified 89 per cent of cases as negative.

Study author Dr Werner Leber from Queen Mary University of London said: “Previous studies have suggested lateral flow tests may be less sensitive than PCR in detecting Covid-19, particularly among asymptomatic individuals and during the early or late stage of an infection when the viral load is lowest.

“But we have found that in patients who are newly symptomatic, the two testing methods have similar levels of accuracy.

“Countries are considering using lateral flow tests to manage future waves of the pandemic. Our findings support this move, but ensuring tests are properly administered should be integral to any strategy.”

Expensive PCR tests are usually required when travelling abroad during the pandemic (EPA)

Dr Jasmina Panovska-Griffiths from the Big Data Institute and The Queen’s College at University of Oxford added: “In our study, both shorter duration of symptoms and higher viral load were significantly associated with positive lateral flow tests.

“This highlights the necessity of testing at early infection with lateral flow tests, and shows that in patients who are newly symptomatic, the two testing methods have similar levels of accuracy.

“Our study is the first study to demonstrate that point-of-care antigen testing using lateral flow tests combined with clinical assessment of symptomatic patients can rapidly and accurately detect Sars-CoV-2 infection in primary care.”

The study included variables such as different brands of test kit, three laboratories being used and professional swabbing undertaken at 20 separate general practices.

It comes after scientists involved in the mass testing pilot in Liverpool said last week that the speed at which test results are available using LFTs compared to PCR tests saved around a day in the time it takes to identify someone as likely to pass on the virus.