Coronavirus rapid antigen lateral flow tests (non-travel)

Rapid antigen tests (also known as lateral flow tests) are diagnostic tests that can detect the presence coronavirus in a swab sample. They’re able to give super fast and reliable results and are a quick, easy and low-cost method of testing.

Nearly 1 in every 3 people with coronavirus do not have any symptoms. These people won’t know they have the virus but can still pass it onto others. This means that a quick and easy test to tell if people who don’t have symptoms carry the virus is very useful to control the spread of the virus and protect those around us. The tests are being used to “screen” people for the virus.

Lateral flow antigen tests in the UK are best used to detect coronavirus in people who don’t have symptoms.

You can use these tests even if you have been vaccinated. We know that vaccines are not perfect at stopping people from getting the virus and people who have been vaccinated can potentially still carry the virus and infect others.

If you have symptoms of coronavirus (e.g. persistent cough, fever, change in sense of taste/smell), you should take a PCR test instead of, or in addition to, a lateral flow antigen test.

If you have had coronavirus confirmed by a PCR test, the NHS recommends that you can avoid regular testing with rapid antigen tests for 90 days.

When using these tests to screen for coronavirus, it is best to take a test regularly. This should be at least once per week and studies suggest best results when testing twice per week.

However, there may also be times when you need to take a test as a “one-off”. For example, when you are coming into contact with a group of people for an event or when travelling.

A rapid antigen test is pretty simple. It’s a test that detects if a specific SARS-CoV-2 (coronavirus) antigen protein is present in a sample from your nose and / or throat.

Wondering how to do a rapid antigen lateral flow test? A small swab is gently inserted into your nose and rotated several times. The swab is then placed into a tube filled with a liquid solution that helps release viral proteins. The swab is removed from the tube and three drops of the liquid solution are added to a test device. The test result should be ready to read within 15 minutes.

Clinical evaluation of lateral flow tests shows that they work best at picking up the virus when a person has high levels of the virus. In most people, high levels of the virus last for 4-8 days and corresponds to when they are most likely to transmit the virus to others.

This test correctly identified people with high levels of the virus in 97% of cases. This means that if 100 people with the virus took the test, we would expect a positive result in 97 of them. Furthermore, almost everyone with a positive test result did actually have the virus – there were virtually no “false positive” results.

However, we do know that lateral flow tests are not as good at picking up low levels of the virus as a PCR test. However, PCR tests have to be done in a lab, take a lot longer to produce a result and are so sensitive that they can be positive weeks to months after people have stopped being infectious.

A positive antigen COVID test will show two coloured lines – usually red, however the colour and intensity of the line can differ slightly. A line should always appear in the C (Control) region, but a positive test result will show a line in the T (Test) region too. Please note the test is invalid if a line does not appear in the C region.

A faint or smudged line in the T region still means indicates a postive result. However, please note rapid antigen tests for COVID tests can show a "false-positive" if the test is read too late - always read the result within 15-30 minutes adding the sample to the test cassette.

If you test positive then it’s highly likely that you’re infected with coronavirus, even if you have no symptoms. You should follow the UK government guidance on what to do if you have a positive test for coronavirus.