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What does a positive Covid test look like? How to read lateral flow test results - and what a faint line means

Lateral flow tests are easy to use and give a quick result

Many people across the UK will now be used to taking lateral flow tests at home for Covid.

But what does a positive Covid test look like and how do you read the results?

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Here’s what you need to know.

What are lateral flow tests?

Lateral flow testing is a fast and simple way to test people who do not have symptoms of Covid, but who may still be spreading the virus.

The tests are easy to use and give a quick result, but those who test positive must currently immediately self-isolate to avoid passing the virus on to others.

They work by detecting proteins (antigens) that are present when a person has Covid.

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 antigens.

How do I take a lateral flow test?

Taking a lateral flow test usually involves taking a sample from the back of the throat near the tonsils and the nose, or just from the nose only, using a swab.

The swab is then dipped into an extraction solution which is dripped onto the device’s paper pad.

The tests give a quick result, as the sample does not need to be sent to a lab.

What does a positive Covid test look like?

If there are two lines, one being next to C and one next to T, even if they are faint, then this means the test is positive (Graphic: Kim Mogg/JPIMedia)

If you have taken a lateral flow test for Covid before you will have noticed it includes letters.

The ‘S’ is where the sample goes and in the separate section above this you will have noticed a ‘C’ and a ‘T’.

If there is one line next to the C then this means the test is negative.

If there are no lines at all or just one line next to the T, then this means the test is void and you will need to retake with a fresh test kit.

However, if there are two lines, one being next to C and one next to T, even if they are faint, then this means the test is positive. You or your test provider must then report this test result to the NHS.

When should I do a lateral flow test?

According to the NHS, you should do rapid tests on days when you’re more likely to catch or spread Covid.

For example, do a test before you:

  • mix with people in crowded indoor places
  • visit someone who is at higher risk of getting seriously ill from Covid-19

You should also do daily rapid tests (one a day for seven days) if you’ve been in contact with someone with Covid and are either:

  • fully vaccinated
  • under 18 years old