What is the difference between Covid-19 rapid flow tests and PCR tests?

IF you think you've contracted Covid-19 there are two ways of testing - you can use a lateral flow test or a PCR kit.

Tests have been hailed as a way to keep Brits safe alongside the COVID-19 vaccine - but what is the difference between the two tests?

As more Brits wish to travel abroad, new rules will come into force on October 4 around Covid-19 testing when returning to the UK. 

The shake-up will see double-jabbed Brits no longer having to take costly PCR tests.

Lateral flow tests will replace expensive PCRs for returning holidaymakers - but travellers will still pay through the nose.

The swabs, only for double-jabbed arrivals, will cost about £30 as the free NHS kits will not be accepted.

Those taking the test will be supervised in person or virtually.

And they will not have to show a negative test at all if they return from a green list country abroad. 

Unvaccinated travellers will still have to pay for a PCR test and face ten days of self-isolation.

Despite most of the new rules coming into force on October 4, PCR tests will be required until the end of October.

What are the differences between PCR and lateral flow tests?

NHS Test and Trace has made rapid lateral flow antigen testing available alongside standard lab-based polymerase chain reaction (PCR) tests.

These tests play a different, but crucial role in the fight against the coronavirus in the UK.

The main differences between PCR and lateral flow Covid tests are:

• The length of time for results
• Accuracy and sensitivity to the coronavirus
• One test is checked in a lab; the other gives an "on the spot" result

Lateral flow

Rapid testing (lateral flow testing) means results are available "on the spot" within just half an hour.

All Brits now have access to these tests and everyone is advised to take two tests each week.

Many employees ask people to test in order to keep themselves and their colleagues safe.

They work in a similar way to the most commonly known lateral flow rapid test strip - pregnancy tests.

A positive result is seen as a dark band or a fluorescent glow on the test strip, with a result in about 30 minutes.

The lateral flow Covid tests are mostly used by people who don’t have coronavirus symptoms (asymptomatic).

A Covid lateral flow test uses a swab from a patient's nose or throat to quickly determine if they are infected with the virus.

About one in three people who have Covid in the UK never show any symptoms - but that does not mean they are not infectious.

This type of test is very good at identifying people who have the virus and are infectious on the day.

If you test positive on a lateral flow test then you need to self isolate and the government says you should then also order a PCR test.

PCR tests

PCR (polymerase chain reaction) tests are the more thorough ‘swab’ tests offered to Brits for more than a year.

The swab can be taken at a drive-through centre or at your home.

It is sent to a laboratory where a lab technician looks for genetic material of the virus using highly specialised equipment.

Results are given in up to five working days by text or a phone call - but it is usually much fast than that.

The PCR tests are much better at finding very small amounts of the virus, especially early during an infection.

So these are used primarily in people who have Covid symptoms.

What are the pros and cons?

Lateral flow tests detect active coronavirus infections, with results in minutes, as no laboratory testing is needed. So you know instantly whether you've got the bug.

Also, they are a "cheap technology and could be a useful tool to identify people with asymptomatic infections who would not otherwise be detected," says the government.

This explains why they're used for rapid testing in communities, schools and workplaces.

But, on the negative side, lateral flow tests only detect people at the most contagious point in an infection.

"Their sensitivity is likely to be between 40–76 per cent, meaning that up to half of infected people may be missed," warns the government.

"The trade-off when using LFTs is that their lower sensitivity means that they are less accurate at identifying people who have an infection," it adds.

What are the other types of Covid-19 tests?

There are two different categories of testing - one finds out if you currently have the disease, the other shows if the person has built up antibodies to the virus.

Aside from PCR and lateral flow testing there are also:

Antigen Tests 

The antigen tests determine whether you have the virus at the time when you take the test. 

These tests look for proteins on the surface of the virus which can be easily found in saliva.

Lab testing isn’t needed for these simple tests, meaning they can be carried out in places such as care homes.

Results can be provided more quickly than PCR tests, with some systems already available and dozens more being developed.

Antibody testing

Antibody tests check if your body has produced any antibodies to fight against the virus.

The test works best on those who have not had Covid-19 symptoms for the last three to four weeks - and uses a blood test to look for antibodies. 

There are pin-prick tests in development which would allow a person to submit their own blood test, but these have not been rolled out yet.

Antibody tests can be booked and paid for privately but are not largely available on the NHS.

Unlike other diseases, the UK government and the World Health Organisation agree there is currently no evidence that someone with antibodies will not catch Covid-19 again in the future.