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PCR test

Written by healthwords.ai's team of doctors and pharmacists based in UK | Updated: 24 Jan 2023 | 2 min read

A PCR test is short for polymerase chain reaction, a test that works by detecting the genetic material of a particular bacteria and virus. If it detects the genetic material of the target infection, then the result comes back as positive.

PCR testing is used for various conditions, including influenza, herpes and COVID-19. It's more accurate for detecting COVID-19 than lateral flow tests, but requires time as a laboratory needs to process the result, rather than a quick test at home.

It identifies people who have a current COVID-19 infection, but it cannot detect if you have had it in the past.

What does the test involve?

A clean sterile swab (a thin plastic stick with a soft end, like a cotton bud) is used to collect secretions from up your nose and at the back of your throat, near your tonsil area. The swab is moved around for 5 seconds in each area. This can be uncomfortable, make your eyes water or make you gag.

The swab then goes into a sealed pot and gets sent to a laboratory to do the PCR testing. It takes between 24 to 72 hours to come back.

Will I keep testing positive?

If you have had COVID-19 within the last 90 days, even once you've cleared it, it's possible that fragments of dead or remnant COVID-19 virus could still be present in your body and may be picked up on a PCR test, resulting in a positive result.

A lateral flow test may turn negative more quickly, and is used to guide people on when they can come out of self-isolation, along with government guidelines.

When should I arrange a test?

If you have symptoms of COVID-19 such as a high temperature, a new continuous cough or a change in your sense of smell or taste then you should book a PCR test, either at a local test site or ordering from the government website. It's free if you have symptoms.

If you have been double-jabbed, you do not need to isolate while you await the result. If you have had no vaccination, you need to self-isolate.

If your PCR COVID-19 test comes back positive then it means you currently are infected with COVID-19 and must isolate. This is regardless of whether you have been vaccinated, but the timing to ending isolating and the lateral flow test required differ, according to your vaccination status.

You no longer need to do a confirmatory PCR test after testing positive on a lateral flow test.