Northern Ireland GP outlines best practice to avoid 'false positive' results on a lateral flow test

By Sophie McLaughlin

A Northern Irish GP has shared her advice on the best way to take a lateral flow test and how best to avoid getting a 'false positive' result.

New rules that came into effect in NI this month, mean fully-vaccinated people who have no symptoms but test positive on a lateral flow device will no longer need to book a follow-up PCR test to confirm

With the reliance on lateral flow tests becoming more integral, Dr Ursula Mason, a GP in Carryduff, explained the best practice for home testing to ensure accurate results.

Speaking to Belfast Live, Dr Mason said: "A false positive is exactly that - the test reads positive when in actual fact, the individual who has taken the test does not have Covid.

"One of the issues around lateral flow testing is that there has been some discussion around how useful and how effective is it but what we do know, and why there has been a switch towards using more lateral flows, is as the rate of transmission in the community increases then the actual level of false positivity in lateral flows will reduce.

"If you get a positive lateral flow test in the current climate where there is high circulating levels of virus, then you can be fairly sure that you have Covid-19 because the probability of that being a positive is much higher."

Dr Mason explained how factors such as eating or before testing can impact results and why it may result in a false positive result.

"The best time to take a test is when there is nothing else in your mouth. What the test is doing is picking up virus antigens in your mucosa, which is the lining of your mouth and nose, so if you have a mouthful of food or have just eaten then you are swabbing and picking up bits of food then you aren't going to pick up the virus.

"You want a clean mouth and if you have a drink of water before you swab, that's actually probably a good thing - one of the things we would suggest is try not to do one just after you eat and in the same way, when you are swabbing your nose it is useful to blow your nose.

"You are looking to swab the lining of your nose and back of your throat so you can pick up any virus that is sitting there and is within your system affecting you," she said.

Dr Mason stressed that not eating or drinking will "increase the probability" of more accurate test results for those who may be asymptomatic.

She continued: "The most important thing is to have access to lateral flow tests and for whatever type of test you are using, read the instructions in the box of lateral flow tests that you have and follow those instructions.

"That will include information around not eating directly before you do it, blowing your nose, washing your hands and making sure that you have your equipment out on a clean surface and that when you are handling it, you are doing it with clean hands.

"This is so that you are not inadvertently causing contamination of the swab before you actually use it on yourself."

Dr Mason concluded: "You are looking to get a good swab of the lining of your nose and the back of your throat and anything you can do that will enhance that then the likelihood increases that you will get an accurate result on your lateral flow.

"If you are doing them regularly, you will get into the way of doing them correctly and therefore the more you do them, the more you can rely on the validity of them and you personally being safe to go out and meet people.

"It's about keeping yourself safe and keeping other people safe around you."

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