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PCR COVID-19 Test: How and When to Use

Written by healthwords.ai's team of doctors and pharmacists based in UK | Updated: 29 Oct 2026 | 2 min read

PCR stands for polymerase chain reaction. A PCR test detects the genetic material of a specific virus or bacterium to help identify an infection.

PCR testing is used to diagnose several infections, including influenza and COVID-19. PCR tests are generally more sensitive than rapid antigen tests, particularly early in an infection. Most PCR tests are processed in a laboratory, so results take longer than those from at-home rapid antigen tests.

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. The swab is moved around for 5 seconds in each nostril. This can be uncomfortable, make your eyes water, or make you gag.

The swab then goes into a sealed test tube 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?

PCR tests can remain positive for up to 90 days after a COVID-19 infection, even after you have recovered and are no longer contagious. This is because the test can detect genetic material left behind by the virus.

If you have had COVID-19 within the past 90 days and develop new symptoms, a rapid antigen test is generally recommended instead of another PCR test.

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 consider getting a PCR test, either at a local test site or by ordering a kit online.

Both PCR and rapid antigen tests can detect COVID-19. If an at-home antigen test is negative, repeat testing may be needed because a single negative result does not rule out infection.

If you have COVID-19 symptoms, stay home until your symptoms have been improving for at least 24 hours and you have been fever-free for at least 24 hours without fever-reducing medication. Take additional precautions for the next 5 days, such as wearing a well-fitting mask and avoiding close contact with people at higher risk of serious illness.

When should I see my doctor?

ou do not necessarily need to see a healthcare provider to get a COVID-19 test. Testing may be available through pharmacies, healthcare providers, and testing centers.

Contact your healthcare provider promptly if you are at higher risk of severe COVID-19, since antiviral treatments work best when started early. Seek immediate medical attention if you develop difficulty breathing, persistent chest pain, or other serious symptoms.

This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.