Lateral flow tests have ‘minimal chance’ of false positives – study

Ella Pickover, PA Health Correspondent
·3-min read

People should be “reassured” that there is a “minimal chance” that tests being rolled out across schools and in the community will give false positive results, ministers have said.

The comments come after a new study claimed that lateral flow tests – a key element of the Government’s Test and Trace programme which is aimed to track down people who have the virus but haven’t got symptoms – will provide less than one false positive result in every 1,000 tests taken.

There are two key assessments for whether diagnostic tools are working – sensitivity and specificity.

Sensitivity is the ability of a test to correctly identify patients with a disease, and specificity is the ability of a test to correctly identify people without the disease.

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The Department of Health and Social Care said that the new analysis show that lateral flow device tests (LFDs) to have a specificity of at least 99.9% when used to test in the community.

Health Minister Lord Bethell said: “New analysis showing that lateral flow tests (LFDs) have a specificity of at least 99.9% when used to test in the community.

“People should use them reassured there’s a minimal chance of a false positive. And that they’re helping us fight the virus.”

Health Secretary Matt Hancock added: “These rapid tests are extremely accurate and are helping dramatically curb Covid cases.”

Millions of lateral flow tests are being used among NHS and care home staff, across businesses, schools, asymptomatic testing sites and at-home testing for the families of school pupils.

Lateral flow tests are quick turnaround tests, which can be performed without the need for laboratory assessment.

Coronavirus graphic
(PA Graphics)

The analysis of LFD tests used data from community testing, rapid testing in educational settings and asymptomatic test sites – in these situations people swab themselves under the supervision of a trained operator.

Dr Susan Hopkins, Covid-19 strategic response director for Public Health England and chief medical adviser to the Test and Trace programme, said: “We know that up to one in three people who have coronavirus never show any symptoms but that does not mean they are not infectious.

“Using LFDs enables us to rapidly identify people in the population who are asymptomatic, with results produced in 30 minutes.

“Lateral flow devices are effective at finding people with high viral loads who are most infectious and most likely to transmit the virus to others.

“We’ve looked very carefully at the evidence that’s emerging from LFD tests that have been delivered at home and in testing sites over recent weeks, and real life scenarios suggest they are at least 99.9% specific, which means that the risk of false positives is extremely low – less than one in a thousand – which is a very good test.”

(PA Graphics)
(PA Graphics)

The Department of Health and Social Care (DHSC) said that testing using LFDs should be a “regular habit”.

But Jon Deeks, professor of biostatistics at the University of Birmingham who has been assessing medical tests for more than three decades, has raised concerns about the tests.

He said: “We also need data from PCR to understand why school positivity rates with lateral flow tests for the past weeks have been as low as one in 1,500 – this is well below what we would expect and raises concerns about the performance of the test in children, for which we have no data.”

PCR (Polymerase chain reaction) tests are swab tests of the nose and throat, which are assessed in a lab setting.