Lateral flow tests, or antigen tests, are the rapid tests which tell people whether or not they have coronavirus.
People faced problems getting hold of the tests last week after a huge surge in demand prompted the government website to say they were “not available right now” for order.
Some pharmacies also placed signs inside their branches saying they were temporarily out of stock.
Meanwhile, health experts have been discussing when is the appropriate time to take the tests as people can change from being testing positive to negative in a matter of hours.
Here are answers to some key questions about lateral flow tests.
What is the difference between lateral flow tests and PCR tests?
Lateral flow tests provide results and tell people in 30 minutes if they have coronavirus by detecting proteins from the virus in the nose and throat samples. Scientists have mixed views on their accuracy but the government says they deliver fewer than one false positive in every 1,000 tests carried out.
PCR tests on the other hand are extremely accurate but take up to three days for results to come through. They detect the genetic material from a specific organism, specifically coronavirus, and are the best way to test if you have a current infection.
Both tests require swabs from your nose and throat (some lateral flow tests only swab the nose).
When should you take lateral flow tests?
According to the Royal College of Pathologists, lateral flow tests should be taken by people who do not have symptoms.
A factsheet on the RCP’s website states: “These tests are very different from PCR. They are not suitable for diagnosing individual patients who suspect they may be infected because they have symptoms.
“People with symptoms need a PCR test. Lateral flow tests are intended for picking up additional infected cases who would otherwise be missed because they don’t have any symptoms.”
On the NHS website, it also says that people who have symptoms of coronavirus should also complete a PCR test rather than a lateral flow test.
Current advice states that if you test positive on a lateral flow you should follow up with a PCR test.
People are advised to do lateral flow tests before mixing with crowds in indoor places or visiting someone who is at high risk of getting Covid-19.
It’s also advised that if you’re vaccinated, but have been in contact with someone who then tests positive for coronavirus, you should do a lateral flow test.
On Sunday, Irene Petersen, a professor of epidemiology at University College London, said official advice should be updated to say that people should take the tests just before they are about to meet others due to the fast infection rate of Omicron.
She added that tests results “expire quickly” as people “may switch from being non-infectious to infectious within hours”.
Government guidance currently recommends taking a test “if you will be in a high-risk situation that day”.
Professor Stephen Reicher told BBC Breakfast on Monday that people should be doing lateral flow tests before meeting up with friends and family this Christmas.
How accurate are they?
A study by the Queen Mary University of London, the University of Oxford, the Institute for Advanced Studies based in Vienna, and the Medical University of Graz published in July found that lateral flow tests detected more than 95% of the cases found by PCR and correctly identified 89% of cases as negative.
In March 2021, the Royal College of Pathologists said positive results by LFTs should be confirmed by PCR tests and people should self-isolate before they receive their PCR result.
Last week, the Health Security Agency (HSA) said lateral flow tests are as likely to detect Omicron as other variants of coronavirus.
PCR tests are still considered to be the most accurate tests when diagnosing coronavirus but should only be used by people who are showing symptoms.
Listen to the ITV News coronavirus podcast
How can you get hold of lateral flow tests?
The NHS has a searching tool which allows people to find their nearest pharmacies which have tests available to collect. It can be found here.
Alternatively, people can order a pack from the goverment website to be delivered to their homes. One pack can be ordered per day.
They can also be collected from community collection points or people can visit a testing point near to their homes.
Is there still an issue with getting hold of lateral flow tests?
Last week, people reported being unable to order lateral flow tests on the NHS website while pharmacies displayed posters saying they had run out of stock.
People trying to book walk-in PCR tests also encountered problems, with some being directed to sites several miles away or being told no slots were available.
Dr Jenny Harries, chief executive of the UK Health Security Agency (UKHSA), downplayed suggestions of a shortage, and said requests for lateral flow tests “have been absolutely astounding”, with “unprecedented demand” for PCR tests.
Sir Chris Wormald, permanent secretary at the Department of Health and Social Care, said issues getting hold of tests laid with distribution, rather than availability.
Lloyd’s Pharmacy, which people said they had found difficulty obtaining tests from, said: “We currently have NHS Lateral Flow tests available and are seeing significant demand for these tests in our pharmacies.
“We would encourage anyone needing a lateral flow test to visit our website to find more information about our range of in store and online Covid testing services and to find their nearest Lloyds Pharmacy.”
Currently, there are no issues with ordering tests on the government’s website - though have reported