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how reliable are they and where can I get a kit?

Alongside booster jabs, lateral flow tests have become the backbone of the UK’s response to the omicron variant – and they have certainly proven popular over the last few days. There has been a run on the tests, with the government distributing more than 2.5 million on Sunday, compared to half a million on the same date in November. 

The government hopes the tests will give people the confidence to meet up with family and friends and enjoy a better Christmas than last year.

But how do the tests work, how accurate are they and where can you get them?

What is a lateral flow test?

Lateral flow devices detect the presence of a target substance in a liquid – in this case the Covid antigen. Sometimes called rapid antigen tests, they look for proteins on the surface of the virus. The virus sample – taken from the back of the nose and throat – are mixed with a solution that unleashes viral proteins. This is then applied to a paper strip which shows up two lines if you’re positive. The technology is well established and is the same that is used in a pregnancy test.

Who should take them?

Lateral flow tests are for people who do not have symptoms of Covid but are worried about spreading the virus unwittingly. If you have symptoms you should do a PCR test. According to the NHS, you should use a lateral flow test if you are going to be in a high risk situation that day – for example, meeting up with friends at someone’s house or in a busy restaurant; . You should also use them before visiting people who are at higher risk of severe illness if they get Covid; or if you are a contact of someone who has tested positive for the virus. 

School children are advised to take a lateral flow test every week and authorities in Scotland, Wales and Northern Ireland are advising that all adults take a test twice a week as well. 

What should I do if I test positive?

Regardless of whether you are positive or negative you should upload your result to the NHS website. If you are positive you should then book a PCR test. There have been reports of people testing positive on a lateral flow and negative on a PCR but lateral flow tests have very few false positive results – that is, they rarely tell people they have the virus when in fact they do not. 

How accurate are lateral flow tests?

Early studies of lateral flow tests raised doubts over their accuracy but later studies using larger datasets confirmed that they would be a useful tool in the fight against Covid. There are two measures to be aware of when discussing testing: sensitivity and specificity. A sensitive test will pick up someone who carries the virus, whereas a specific test will pick up someone who does not have the virus.

Lateral flows have high sensitivity and do not give many false positives, however they do give false negative results. 

A Cohcrane review of 64 studies found that they correctly identify 72 per cent of infected people who have symptoms, and 78 per cent within the first week of becoming ill. 

Tim Peto, professor of medicine at the University of Oxford and the senior author of another study earlier this year that showed the tests were able to pick out nine out of 10 infectious cases, said: “We know that lateral flow tests are not perfect, but that doesn’t stop them being a game-changer for helping to detect large numbers of infectious cases sufficiently rapidly to prevent further onward spread.”

John Edmunds, professor of epidemiology at the London School of Hygiene and Tropical Medicine, said of the tests last week: “They’re an incredibly useful tool. I think they’ve had a very poor press for some reason. It is undoubtedly the case that they are less sensitive than the PCR tests. But there’s a strong argument that PCR test is actually over sensitive in many respects.”

Can I trust a negative lateral flow test?

Lateral flow tests pick up positive cases when the virus is at its peak – so if you test very early on in an infection it may not pick the virus up. You may also be doing the test incorrectly. If you are unsure you should repeat the test – and if you have symptoms you should do a PCR test. 

Can a lateral flow test detect omicron?

A lateral flow test cannot tell you which virus variant you have – it cannot distinguish between delta or omicron, for example. But if you are infected with the omicron variant it will tell you if you are positive or negative. To know whether you have omicron specifically you will need to do a PCR test as these are more sophisticated and detect the genetic material of the virus, rather than just the presence of a virus. 

How do I do the test?

Follow the instructions in the test kit and do not eat, drink or smoke 30 minutes before testing. Wash your hands with soap and water and wipe down the surface you are going to place your kit on. Blow your nose and then wash your hands again.

If you have to do a throat swab open your mouth wide and rub the wab over your tonsils. Then put the swab up your nose – about 2.5cm. Put the swab in the test tube that came in the kit, squeeze the liquid onto the test kit and wait 30 minutes. Two lines means positive and one means negative. For full instructions click here.

Where can I get hold of the tests?

Like toilet paper and hand sanitiser at the beginning of the pandemic, lateral flow tests have become the latest Covid gold dust item. You can order them online here. In the last few days they have been unavailable but under normal circumstances you should be able to order one pack a day. You can also pick up two packs at a time from pharmacies, community centres such as libraries and test sites although many venues have reported shortages. Pupils and students can also pick them up from schools and colleges. 

They are likely to be in greater demand over the coming weeks as people socialise more and with new government guidance which states that if you have had two doses of vaccine or are under the age of 18 you do not have to self isolate if you live with someone who has Covid. Instead, you are “strongly advised” to take a lateral flow test every day for seven days.

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