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. Anecdotally, as doctors we've found that PCR tests usually turn positive a couple of days before a lateral flow test.
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.
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 falsely 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.
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 your PCR test comes back positive, it means that you are currently infected with COVID-19 and avoid others and isolate for at least 5 days. This is regardless of whether you have been vaccinated, but this is not a legal requirement for those living in England. The government requests everyone take responsibility for themselves to prevent spreading the infection, and should therefore avoid others while they could be contagious. Others eligible to order a free PCR test are those with certain health conditions that mean they may receive COVID-19 treatments, if you live with someone who has tested positive for COVID or has COVID symptoms, or if you have been advised to do so by a doctor, local authority or Test and Trace advisor. You no longer need to do a confirmatory PCR test after testing positive on a lateral flow test. PCR tests may be required for travelling abroad or returning to the UK, but these must be privately funded and arranged.
You do not need to see a doctor for a PCR test. If you are in the UK and have COVID-19 symptoms or have been advised by your local authority or doctor to get a test then you can book a free test online or by calling 119. PCR testing is also available privately. *Information correct on 1st March, 2022