Lateral flow device (LFD) testing is a fast and simple way to test people who do not have symptoms of COVID-19, but who may still be spreading the virus. In some circumstances lateral flow tests can also be used for other diagnostic tasks.
The tests are easy to use and give results in 30 minutes. Those who test positive must immediately self-isolate to avoid passing the virus on to others.
Why lateral flow tests are being offered?
Around 1 in 3 people with COVID-19 do not have symptoms, so a test that rapidly detects these otherwise hidden cases is a very useful additional tool for tackling the virus.
Lateral flow tests are practical, easy to interpret and can be used in a wide range of settings. This makes them ideal for widespread use in the community.
Clinical evaluation by Public Health England (PHE) and Oxford University shows that the tests perform best when levels of virus are at their highest. Thousands of positive COVID-19 cases have already been detected using these tests.
Each positive case identified can help prevent many additional people becoming infected over time.
How lateral flow testing works
Lateral flow is an established technology, adapted to detect proteins (antigens) that are present when a person has COVID-19. The best-known example of a lateral flow test is the home pregnancy test kit.
The test kit is a hand-held device with an absorbent pad at one end and a reading window at the other. Inside the device is a strip of test paper that changes colour in the presence of COVID-19 proteins (antigens).
Taking a lateral flow test usually involves taking a sample from the back of the throat near the tonsils and from the nose, using a swab.
The swab is dipped into an extraction solution. This is then dripped on to the device’s paper pad, producing the reaction that gives the result.
The result will be visible on the device precisely 30 minutes after the sample is applied. Unlike a PCR test, there is no need to send the sample to a lab.
If you do have symptoms of COVID-19 you should not visit an asymptomatic test site. You should self-isolate immediately and follow the guidelines:
Get a PCR test here to confirm if you have coronavirus when the following apply:
you have a high temperature
you have a new, continuous cough
you’ve lost your sense of smell or taste or it has changed
How effective is lateral flow antigen testing?
Lateral flow tests can help to drive down the spread of COVID-19.
Lateral flow tests deliver a rapid result, in 30 minutes. They can find positive cases with high levels of virus that are easy to transmit to others, helping to intercept and reduce further infections.
How sensitive are the tests?
‘Sensitivity’ refers to the proportion of people with COVID-19 that have a positive test.
When a person has low levels of virus in their system, lateral flow tests are less sensitive than some of the other tests we use, such as PCR tests which we mainly use for people with symptoms.
When levels of virus are at their highest and people are most likely to pass on the disease, lateral flow tests can detect the vast majority of cases.
PCR and lateral flow have different roles to play in controlling the virus, so it isn’t helpful to directly compare them in terms of how sensitive they are:
Lateral flow is useful for finding out if a person is infectious now, and able to transmit the virus to others. The level of sensitivity is high enough to detect the vast majority of these cases. Lateral flow testing is less likely to return a positive result outside the infectious window.
PCR is useful for confirming a suspected case of coronavirus, where the person is already self-isolating and is showing symptoms. Higher sensitivity of PCR means it can identify genetic material from COVID-19 even after the active infection has passed.
The different levels of sensitivity are therefore appropriate for the ways they are used.
How lateral flow testing was trialled
The tests underwent a rigorous validation process including evaluations from Public Health England and the University of Oxford. The Medicines and Healthcare products Regulatory Agency (MHRA) provides ongoing regulatory oversight.
Trials were carried out on the tests in a wide range of environments.
Large-scale pilots have also been carried out, including the whole city pilot in Liverpool in November 2020. As a result of the pilot, 897 positive individuals who would not otherwise have known they were infected, tested positive using lateral flow tests.
Watch the video below to see how Lateral Flow Testing Works in our Test Centre
View or download the government guidance for testing at home below: