What is the difference between a PCR test and a lateral flow test?

A man uses a swab to take a sample for a Covid test in London. PCR tests are expected soon to be scrapped for travellers and replaced with lateral flow tests. AFP

PCR tests have been made compulsory for all travellers arriving in the UK as a way to fight the newly discovered coronavirus Omicron mutation.

Accepting only PCR tests means the price goes up for the travelling public as the previous option — a lateral flow test — was cheaper. There are also differences in the time it takes to obtain results and accuracy rates.

UK Prime Minister Boris Johnson announced the move to only PCR on Saturday, a day after the World Health Organisation called Omicron a “variant of concern.”

“We're not going to stop people travelling, but we will require anyone who enters the UK to take a PCR test by the end of the second day after their arrival and to self-isolate until they have a negative result,” Mr Johnson said.

The devolved administrations in Scotland, Wales and Northern Ireland have adopted similar measures for travellers.

So what is the difference between the two tests?

Price tag

Polymerase chain reaction, or PCR, tests cost about £65 ($86) and in-store ones retail for about £85. Private clinics tend to charge about £200 per test.

These prices are significantly higher than for lateral flow tests which can be sold for anywhere between £5 and £30.

When PCR tests were scrapped in favour of lateral flow tests, the move saved families hundreds of pounds per trip.

Taking the test

Both require a swab to be taken from the nose or throat.

For a PCR, the swab has to be sent to a laboratory where researchers analyse it and the result is delivered to the customer, usually be email.

This can take up to two or three days, depending on whether there are any backlogs in labs.

The LFT swab on the other hand is inserted into a capsule of liquid before being poured into a device. The rapid tests have been used in schools and workplaces and for allowing entry to events.

Advice varies but most manufacturers say to wait about 15 minutes before accepting the results displayed.

Test results

PCR test results are sequenced in labs to pick up variants of concern and that includes the Omicron mutation. This is why they are recommended for people experiencing Covid symptoms.

Because of their high reliability in this regard, the UK government was, for a long time, reluctant to replace them with LFTs.

The government also realised the quality of lateral flow tests has improved since the start of the pandemic.

Travel companies have long said that pricey PCR tests are deterring people from booking flights abroad.