Briefing on Lateral Flow Testing

In the first week of November, Government announced the roll out of one of several new ‘rapid tests’ it has been developing for COVID-19. One of these rapid tests, or Lateral Flow Tests (LFTs), was used in England’s first large scale community screening pilot in Liverpool. An initial batch of 10,000 of these tests is being made available to councils expressing an interesting in participating in a further roll-out of these tests and who are able to test at least 10 per cent of their local population every week. In the second week of November, Government announced that a further 66 areas would join Liverpool, with more being added.

Lateral flow test kits are due to arrive imminently with directors of public health in England for them to direct and deliver expanded asymptomatic community testing in line with their local priorities, which will include high risk and priority groups. Lateral flow tests can also to be deployed in Universities to enable students to return home safely for Christmas. Government has written to Universities to say that that student testing can begin on 30 November and run until 6 December – referred to as a “pre-end-of-term testing” period. This means some students could begin returning home immediately after a negative test, although those who tested positive would have to self-isolate.

The current “best standard” test is the PCR (polymerase chain reaction) test which tests for evidence that the virus is currently in your body. This is the test presently available at local test sites, and is used in care homes and the NHS, and requires laboratory analysis before a result is provided. Lateral flow tests are  typically rapid tests which provide results in less than an hour, and are often compared in appearance to a  home pregnancy kit. LFTs are administered by someone placing a nose or throat swab into a tube with a reagent liquid to create a solution.  This solution is then dropped onto a test cartridge which contains antibodies to coronavirus; if the solution from the swab contains coronavirus, that bonds with the antibodies and a chemical reaction creates a coloured line inside the cartridge window which indicates a positive result.  

Testing remains one key plank of a combined strategy (Test, Trace, Isolate, Social Distancing, Hygiene and Face Coverings) to combat COVID-19 until a vaccine is in place

The advantages of LFTs  are that:

• they give local public health teams the opportunity to increase rapid case finding across their area through mass screening , without the need for f laboratory processing, and supporting those who have the virus to self-isolate;
• by proactively testing asymptomatic individuals, they increase  potential to not only break chains of transmission, but also help to protect and enable our critical businesses, , key workers and institutions to continue operating as effectively as possible
• for those opting for a lateral flow test,  this test is a non-invasive procedure and the results back are extremely quickly (around an hour);
• they contribute to our wider understanding of the prevalence of COVID in our population

Government’s evaluation at the time of writing suggest that the lateral flow test used in Liverpool, and for distribution to directors of public health, are accurate enough to be used for community testing. At the time of writing, we understand that where a person has a positive result from a lateral flow test, they will require a confirmatory PCR test. We will update this note if this advice changes.

While the Government’s evaluation report makes it clear their selected lateral flow test is suitable for community use, there is debate in the public health and academic community about factors which may impact on the reliability of the test and how to mitigate any impacts from false positives, or false negatives