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How COVID-19 lateral flow tests work and their role in our national testing programme.

First published:
23 February 2021
Last updated:

Overview

Lateral flow test (LFTs) are used to identify people with COVID-19 who are not showing symptoms. Around 1 in 3 individuals with COVID-19 do not have any symptoms. If left undetected they will continue to spread the virus.

Testing those without symptoms is an important tool in the fight against coronavirus. Each positive case identified can help prevent many more infections.

LFTs are easy to use and give results in 30 minutes. They are easy to interpret and can be used in a wide range of settings.

How lateral flow testing works

Lateral flow is an established technology, adapted to detect proteins 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 if COVID-19 proteins are present.

How to take the COVID-19 lateral flow test

Video: how to self-test

Watch a short video demonstration of how to take the test.

You need to use a swab to take a sample from the back of your throat and from your nose.

Once you have taken the sample, you dip the swab into an extraction solution and then onto the lateral flow test’s paper pad.

You will see the result on the device 30 minutes after you have applied the sample. There is no need to send the sample to a lab.

How to interpret the results

Image
Image showing the results a lateral flow test might show

 

Negative result: 1 line next to C

Positive result: 2 lines, 1 line next to C and 1 line next to T

Even faint lines mean that your test is positive for COVID-19.

You or your test provider must report this test result (positive or negative) to the NHS.

You, or your test provider, must report your test result - to the NHS

Void:  No lines or 1 line next to T. This means the test is invalid. Re-take the test with a fresh test kit.

A negative result does not guarantee that you do not have coronavirus. The test might not detect the virus if you were recently infected or are in the incubation at the time of the test.

You must continue to follow coronavirus rules, including:

  • regular hand washing
  • social distancing
  • wearing face coverings where required

What to do if you have a positive lateral flow test result

If you get a positive lateral flow test you must self-isolate immediately for 10 days and take a PCR test at a test centre within 24 hours. You can book a test online on GOV.UK, by calling 119 between the hours of 7am to 11pm (calls are free) or via the NHS COVID-19 app.

If your PCR test is negative and taken within 24 hours of your lateral flow test, you can leave self-isolation.

If your PCR test was negative but was taken more than 24 hours after your lateral flow test you and your contacts must remain in self-isolation for the full 10 days from the date of the original lateral flow test. 

If your PCR test is positive and taken within 24 hours of your lateral flow test, you must stay in self-isolation for 10 days from the original lateral flow test result.

If you don’t take a PCR test within 24 hours you must self-isolate for 10 days.

Who can be tested?

Lateral flow testing is currently being offered to people who don’t have symptoms, in a range of different settings. They are being used for regular testing of NHS and social care staff, as well as in universities, schools, care homes and other workplaces.

People who cannot work from home can also get tested regularly.

Get rapid lateral flow COVID-19 tests if you do not have symptoms.

How accurate are lateral flow tests?

Lateral flow tests are validated technology. Extensive clinical evaluation from Public Health England and the University of Oxford show Lateral Flow Tests (LFTs) are specific and sensitive enough to be deployed for mass testing, including for asymptomatic people.

How sensitive are the tests?

The lateral flow tests cannot detect very low levels of coronavirus in a sample. This means if you have only recently been infected, are in the incubation period, or if you have mostly recovered, the test may not give a positive result

Test sensitivity for lateral flow tests is also dependent on the person who does the test. Training and regular use helps to mitigate this as people become more proficient in using lateral flow tests.