LATERAL flow tests are in high demand as the Omicron variant spreads like wildfire in the UK.

The Government advises taking them whenever you are going to an event where you could spread Covid to other people – such as a Christmas party.

However, it’s likely you have already heard that the 30-minute tests are not 100 per cent accurate.

Even if you get a negative result with lateral flow, also known as an antigen test, this does not necessarily mean that you do not have the virus and can spread it to others.

Occasionally it will give what’s known as a “false negative”.

A “false positive” on the other hand, is very rare. If your test produces a positive result, is it very likely that you have Covid and need to get a PCR test to confirm it.

It has emerged that lateral flow tests could be less effective in picking up the Omicron variant, which would be a huge blow to keeping it contained.

Dr Angelique Coetzee, chair of the South African Medical Association, said she believes the rapid Covid tests aren't always picking up the variant.

She told a Science and Technology Committee on Tuesday: "The rapid test still showing false negatives in the early period.

"We do have patients that waited a week and still have a headache and then they do PCR and it's positive."

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But UK health chiefs disagree with the comments, and say early studies using people infected with Omicron show the at-home kits work.

 UK Health Security Agency Dr Susan Hopkins said: "Lateral flow devices will detect in asymptomatic as well as symptomatic infection.

"They've been used very effectively now for almost one year in the UK population.

"What we know is that overall it will detect about 50 per cent of cases compared to PCR, but it will detect about 80 per cent or even more than that of people who have high amounts of virus and therefore are at the highest risk of transmitting to others.”

Small tweaks, big difference 

With tensions high before Christmas and fears of self-isolation over the big day, taking a lateral flow properly could make a big difference.

The Department of Health says you should take your lateral flow test according to the instructions in the packet.

There are various manufacturers of the test, and how to take them may vary slightly from one to the other.

Some only need a nasal swab – however, one doctor has raised concern that tests that only use a nasal sample are less correct.

London-based A&E doctor Nathan Hudson-Peacock, who goes by @expedition_doctor on Instagram, posted an image of four lateral flow tests, two of which were positive.

He wrote in the caption: “Interestingly, these LFT kits were meant to be done as a nasal swab. 

“However, as an experiment, I decided to do 2 of them as throat swab instead. 

“The 2 positive tests are throat, the 2 negative ones are nasal. 

“While this isn’t official advice and is my view only, it would seem reasonable to do one swab as per instructions, as well as a SEPARATE throat swab if you want to be extra careful around loved ones.”

Meanwhile, another medic has urged people not to be complacent when using the lateral flow tests before seeing friends and family.

Billy Quilty, an infectious disease epidemiologist at London School of Hygiene and Tropical Medicine, suggested that taking a lateral flow test the day before an event – or even in the hours leading up to it – may be too early.

He posted an image of two negative tests that were taken in the morning and at lunch time, which were both negative. 

By the same evening there was a very faint positive result, and the next morning it was clearly positive.

Dr Quilty wrote: “A demo of how fast you can turn positive. Do LFTs *just* before meeting up.”

How to take a lateral flow

The testing kit comes with instructions and is fairly simple to use.

You need to make sure all surfaces and your hands are clean before taking the test to avoid any contamination, which could skew results.

Try not to eat, drink, smoke or vape 30 minutes before doing the test as this may affect the result of some tests.

Once you have opened the kit, use it within 30 minutes.

It first involves taking a swab of nose and/or throat.

You'll want to make sure you do the swab correctly so you don't mess up the sample.

The instructions will clearly tell you how far up your nose you need to insert the swab, but it is usually until you "feel resistance".

For the throat, it's important to only roll the swab on the tonsils and not touch the tongue or other parts of the mouth.

The swab is dipped into a solution before this is placed onto a paper pad on a device that looks like a pregnancy stick.

Inside the device is a strip of test paper that changes colour if coronavirus proteins are in the sample.

Usually, one line next to the "C" means negative, two lines next to "C" and "T" means positive, and no lines or one next to "T" means the test is void.

Can you trust a lateral flow test?

The rapid at-home tests have given the UK a huge advantage in keeping on top of Covid in that they help to spot the virus much more quickly. 

A lateral flow test is going to give you the best indication of whether you have Covid or not – other than if you had symptoms, in which case you’d get the highly accurate PCR test.

The Department of Health says the tests have been rigorously assessed by scientists. This means they are "accurate, reliable and successfully identify those with Covid-19 who don’t show symptoms".

But the tests were not designed to look for Covid in people without symptoms, but for people who do have symptoms, therefore they cannot always be correct.

To be on the safe side, do a couple of tests just before you see people outside of your home – such as your family or friends at the pub.

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