fbpixel

COVID-19 PCR Testing Explained

Frequently asked questions about COVID-19 PCR testing.

Written by Dr Adam Abbs. Last updated 15/03/2021.

What is a PCR test?

A Covid-19 polymerase chain reaction (PCR) test looks for the Covid-19 virus on a swab sample collected from the back of the throat and nose. It works by detecting the genetic material in the virus called RNA. 

What is the difference between PCR-swab and Lateral Flow tests?

  • PCR swab tests look for genetic fragments (RNA) of the virus. They will pick up most, but not all, positive cases. They are useful when somebody isn’t sure if they have Covid-19.
  • Lateral flow tests look for proteins produced by the virus called antigens. They may miss more positive cases than PCR swab tests, but they can be done quickly and easily. They are useful when somebody thinks that it is unlikely that they have Covid-19 and need a quick answer. 

How is a PCR test administered? Is it painful?

A PCR test involves inserting a thin, flexible stick with a cotton tip into your nose in order to sample any fragments of viruses. The swab is rotated several times in both before being withdrawn and it is then sealed in a tube to be sent to a lab for analysis. This can be somewhat uncomfortable but is not overly painful, and it only goes 2-3 cm into your nose. 

PCR testing works by detecting the genetic material found in coronavirus (RNA).


Who can get a PCR test?

Anyone can take a private PCR test at any time. You will need to have coronavirus symptoms to get a PCR test on the NHS. If you have symptoms of COVID-19, it is important that you stay at home and follow government guidelines here.

I have COVID-19 symptoms, is a PCR test the right test for me?

Yes, if you currently have symptoms this is the most appropriate test.

When should I get a PCR test?

Anyone with symptoms should be tested, wherever possible. People who do not have symptoms but have had close contact with someone who is, or may be, infected may also consider testing. Testing may also be undertaken to allow someone to enter a workplace, or to travel. 

Can I buy a PCR test for someone else?

If other people you live with have symptoms, you can order tests for up to 3 of them. Make sure the person you’re buying the test for has consented to this.

Is it safe for my child to get a PCR test?

All children can be tested using a PCR test kit, but children under 11 will need to be helped by their parents or carers if using a home testing kit. Children and teenagers who have symptoms of Covid-19 should be tested immediately to determine if they have Covid-19, particularly if they are participating in sports or going to school or a workplace so that effective tracking and tracing can be carried out. 

PCR testing is recommended for children and can be carried out safely at home by a parent or guardian.


Can my child go back to school if they have tested negative for COVID-19?

If your child tests negative following an infection, and they don’t have symptoms they can usually return to school following the isolation period. If your child tests negative but remains unwell, they should not return to school until they have fully recovered. 

What are the limitations of PCR testing?

No test is 100% reliable, even those done to the highest standards. If you are unsure of what a test result means, or what you should or should not do once you have received your test result, you should first contact the provider of the test, and if you remain unsure then speak to your GP or a healthcare professional. 

Can having the vaccine result in a positive PCR swab test? 

No, the current vaccines would not cause your Covid-19 PCR swab test to be positive.


Positive Test Results

How long does it take to get the PCR test result?

PCR tests take only a few hours to complete. However, they often need to be transported to large laboratories, so it can take a few days to get your results. On average, you can expect to receive results from a PCR test within two to five days. However at Medicspot we are working hard to shorten this waiting period, so Medicspot currently offers a PCR testing service with results guaranteed within 24 hours. Click here to find out more. 

How will I be contacted about my PCR test result?

If you are tested by the NHS, NHS Test and Trace will contact you directly. All texts or emails will ask you to sign in to the NHS Test and Trace contact-tracing website. If NHS Test and Trace call you by phone, the service will be using the phone number 0300 013 5000.

PCR tests are crucial for use in surveillance of the virus, and are also important for contact-tracing since.


What does a positive PCR swab test result mean?

A positive test result means that there is evidence of genetic material of Covid-19 in your airways. This is usually interpreted as meaning that you are infected with Covid-19.

How accurate is a positive PCR swab test?

A positive result is correct nearly 100% of the time. However, it may remain positive after the virus has cleared.

What should I do if my PCR test result is positive?

If you receive a positive PCR test you, and anyone you live with, must self-isolate to avoid spreading the infection to other people. The self-isolation period includes the day your symptoms started (or the day you had the test if you do not have symptoms) and the next 10 full days. If you live in a care home or in supported living, you may need to self-isolate for 14 days instead of 10. You must inform your employer, school or nursery of your result. 

I took two PCR swab tests, one is positive and one is negative, which one is correct?

The positive test. A positive PCR test result is more reliable than a negative PRC test result, so where there are two tests, we need to treat the positive test as the correct one.


I took a PCR swab test, which was positive, and a lateral flow test, which was negative. Which one is correct?

The PCR test is correct. The lateral flow tests can miss upto 50% of positive cases, so they should not be used in patients who have symptoms or who have a positive PCR swab test. Lateral flow tests are less accurate but useful in giving a quick result in a well patient. 


Negative Test Results

What does a negative PCR swab test result mean?

A negative test result means that there was no evidence of genetic material of Covid-19 in the swab of airways. This is usually interpreted as meaning that you are not infected with Covid-19.

What should I do if my PCR test result is negative?

A negative result means the test did not find signs of coronavirus. You do not usually need to self-isolate if you get a negative result. But this does not guarantee you do not have Covid-19, so you must keep following all social distancing advice


If you still feel unwell after a negative test, you should stay at home until you're feeling better. Contact a GP if your symptoms get worse or do not go away. If you develop coronavirus symptoms after the test, you must get tested again. 

How accurate is a negative PCR swab test?

The PCR swab tests are considered accurate, but they do miss some positive cases (upto a quarter of cases), which means that a negative result is not always correct. So you still need to follow isolation advice if you have symptoms, contact with a positive case or a positive test. 

How can I be negative if my partner/relatives have tested positive?

There are many potential causes for this, including:

  • Your negative test is a “false negative” (meaning that you have Covid-19 but the test didn’t pick it up) which is why you still need to isolate if you have had contact with a positive case.
  • You are in the very early stages of your infection, in the “incubation” period, before the tests will identify that you have Covid-19. If you test again in a few days it may well be positive. 
  • You could have just cleared the infection. 
  • Maybe you have had Covid-19 previously, and have antibodies, so have some immunity.

I have a negative test but I have been told that I cannot be provided with a fit to fly letter. Why is this?

The fit to fly letter is more than just a repetition of the test result. A doctor may not be able to certify you as fit to fly for a number of reasons, including:

  • You have had a positive test in the previous 10 days
  • You have come into contact with a positive case within the previous 10 days
  • You have had symptoms in the previous 10 days
  • You are clinically vulnerable and therefore at higher risk of contracting Covid-19 on an airplane
  • You cannot wear a mask to protect yourself during your journey
  • Any medical reason why you would not be safe to travel

Can I use a negative test result to reduce my isolation period if I have been told to isolate?

No. As the negative PCR swab test misses upto a quarter of positive cases, you are still classed as at risk of having Covid-19.

Void or Invalid Test Results

What should I do if my PCR test is void or invalid?

If you had a PCR test and your sample could not be read, you will need to take another test as soon as possible, and should self-isolate until you get the result of the second test if: 

  • You had a test because you had symptoms
  • Someone you live with has tested positive or has symptoms and has not had a negative test result
  • You have been told you have been in contact with someone who tested positive
  • You are in quarantine because you have recently travelled to England from abroad 

When can I redo my test?

Anytime. But be aware that even after the virus has cleared it usually takes over 2 weeks before the genetic material of the virus is no longer detectable in your airways. Some people continue to have a positive test result for 3 months.

Medicspot’s PCR testing service

Does Medicspot offer a private COVID-19 PCR test?

Yes. We provide PCR swab testing. Our private Covid-19 testing is provided by UKAS-accredited laboratories, using CE-approved PCR assay machines to provide fast and reliable results that clients can have confidence in.


You can reserve a Medicspot Covid-19 PCR test kit for instant collection at your nearest Covid test centre and receive your coronavirus results next-day by 11:59 pm.

How does your at home PCR test work?

Simply book your Covid PCR test online and reserve your test kit for instant collection. Pick up your test kit from your nearest Covid test centre. Perform your test at home and drop-off your kit using the security seal and return label provided. You will then receive your results via email. Depending on your result, you may also receive a test results certificate. Click here to watch a video demonstration of how to take a Medicspot Covid-19 PCR test at home. 

What does the PCR test kit include?

Your private test kit will include instructions, a cotton swab, sample tube, clear sealable bag and a return box with a security label.


Our Priority Courier Covid-19 test includes next-day delivery in the UK which is accepted by all major airlines and workplaces.

How much does a private PCR test kit cost?

Both of the test kits we provide cost £149 with next day results.

When will I get my test result?

After we have received and tested your sample at one of our labs, you will receive your Covid-19 test results next-day by 11:59 pm via email.

Does your PCR service use accredited labs?

Yes, our PCR service uses UKAS accredited laboratories. The United Kingdom Accreditation Service (UKAS) is the sole national accreditation body for laboratories, recognised by the government, to assess standards of certification, testing, inspection and calibration services.

Where can I get a private PCR test near me?

We have a range of private Covid test hubs located across the UK which allow you to pick up and drop off your Covid-19 PCR test kit at any time. To find your nearest Medicspot Covid test centre click here

Travel and PCR Testing

Are PCR tests acceptable for travel?

PCR tests are acceptable for travel however you will need to find a test provider that meet the standards for pre-departure testing. The test must meet performance standards of ≥97% specificity, ≥80% sensitivity at viral loads above 100,000 copies/ml. It is your responsibility to make sure the test meets the minimum standards for sensitivity, specificity and viral load details so you must check with your test provider that it meets these requirements. Up to date guidance for each destination including entry requirements can be found here

Travelling abroad should be limited unless deemed essential. It is important to follow strict national guidelines by maintaining the use of face coverings, keeping a safe distance from others and disinfecting hands often.


Can I travel if I receive a negative PCR test result?

You can travel if you have a negative test result, however, if you are boarding a flight, this must be accompanied by a fit to fly certificate signed by a doctor. For more information on how to obtain a fit to fly certificate with Medicspot click here. At present, it is important that you follow government advice and stay at home and not leave home to travel abroad, except in exceptional circumstances. 

I have had the vaccine, does that mean that I am safe to travel without testing?

No. Current guidance is that the restrictions on travel are the same for those with or without the vaccine. This may be subject to change, so check the NHS website for updates.

Need a private Covid test?

Medicspot is the leading provider of private Covid testing in the UK.

Get a private Covid test