Lateral flow test: How the test works – advantages and disadvantages according to expert

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Rapid lateral flow tests help to find cases in people who may have no symptoms but are still infectious and can give the virus to others. The test usually involves taking a sample from your tonsils and from your nose, using a swab with a result in as little as 30 minutes. Professor Iain Buchan, Professor of Public Health and Clinical Informatics, Institute of Population Health, University of Liverpool spoke exclusively with Express.co.uk to discuss further how lateral flow testing works and if there are any advantages or disadvantages to this type of testing.

Lateral flow tests are used to identify those people who have the virus, but no symptoms, and it is believed their widespread use could identify cases and stop transmission.

In recent news, parents of schoolchildren have asked if it is possible to test themselves for COVID-19 twice a week.

In a letter, director of public health Jim McManus asked them to use lateral flow tests to help “identify outbreaks more quickly and effectively”.

Indeed, this type of testing is far quicker however it safer?

When asked what lateral flow testing is, Professor Buchan replied: “Lateral flow is a type of test for detecting the substances that the immune system deems it as foreign, and attacks known as antigens.

“The SARS-CoV-2 virus that causes COVID-19 disease has a protein on it that acts as the antigens that the body’s immune system uses to recognize the virus and neutralizes it, for example with antibodies.

“The lateral flow test has a line of antibodies manufactured to make an antigen from SARS-CoV-2 stick to them, and this changes color when that happens.

“The line is part way along a strip and fluid flows laterally to it from a well where a special solution washed around a nose/throat swab is added.

“The travel of the fluid picks up various ingredients needed for the reaction that will change the colour of the strip if the virus antigen is present.

“The commonly used tests are made to pick up an antigen from the nucleocapsid or N protein that covers the inner part of the virus – this has not changed much while the virus has been mutating so the common lateral flow tests pick up the new variant.

“Lateral flow tests are only usually positive when a person is shedding the virus from their nose and throat – the time when they are likely to pass it on.”

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When it comes to the main benefits of this type of testing, Professor Buchan said: “The main benefits are rapid, sufficiently reliable results, not requiring a laboratory, and low cost.

“Results are available within 30 minutes not the one to three days that typical lab-based test results take to come back.

“The kits can be manufactured quickly in vast quantities at very low cost, so they can be used regularly, which is the best way of identifying people who are likely infectious and giving them the opportunity to isolate, thereby breaking chains of infection.

“The tests typically pick up eight or nine out of every 10 people tested who are likely infectious.

“Given their low cost and flexible use, tests are easily repeated when there is a greater need to be sure of picking up as many of the infectious people as possible.”

Asked why they are being offered during this time, Professor Buchan replied: “This fast speed and large potential scale of identifying infectious people is a way of making the opening up of businesses and social spaces safer after lock-down, provided all of the people using the tests understand that a negative result is not a signal to stop paying attention to hands, face, space.

“The flexibility and low cost of testing means that local public health teams can work with communities to make best use of the tests as the needs for testing change over time with phases of the pandemic.

“Similarly, business and workplaces have flexibility to work with their staff and customers to make testing fit their business, in consultation with public health authorities.

“As home test kits and apps to read test results become common the testing flexibility should increase further.

“Rapid testing is about helping reduce risks by identifying people who are infectious, enabling them to isolate and not pass on the virus.

“Vaccines and tests work together to protect society and reduce risks. If testing is applied well, as part of comprehensive public health programmes, it will also preserve vaccines, because faster spreading virus is more likely to become smarter in evading or escaping new vaccines.”

When it comes to any disadvantages one should be aware of when it comes to lateral flow testing, Professor Buchan warned: “Tests are only as good as how they are used.

“If communication is not clear that a negative test result is not a license to drop COVID-safe behaviours then they will not reduce risks as intended.

“Similarly, if people are not supported properly to isolate then they may not come forward for testing or may not isolate after a positive result.

“People from the most deprived areas tend to take up testing less than those from the more affluent areas, and have less resources to be able to isolate, so testing can increase inequalities.”

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