How to interpret your PCR test

Dr Joachim Stolte

Published: 10/01/22

You may have had a PCR test and received a negative result, but it’s possible to find that a test taken a day later is positive.  Why is this?

The Covid virus can take a while to incubate.

When you’re infected with Covid after you’ve been exposed to someone with the virus, it can take a while before you test positive.  This is because within the first few days there’s not enough of the virus’s genetic material to be picked up in a PCR test.  

Your PCR test will tell you your status at that moment in time, however if you are incubating the virus it’s possible that you could test positive on a subsequent test, even one taken the next day.

You can transmit the virus before you know you are infected.

One of the frustrating issues with Covid is that we can be asymptomatic for up to 2 weeks (although it’s usually less than this), but still able to spread the virus to others.  

The average time from exposure to a positive test is 3-5 days, so if you are booking a PCR test, be mindful that if it is within 3-5 days of potential exposure you may get a ‘false’ negative.

Your PCR can still test positive long after you’ve had the virus.

It has been documented that some people can test positive for weeks after having had Covid. This is despite them being asymptomatic and unable to transmit the virus to others.

In one documented case, a patient was still ‘shedding’ (or expelling particles of the virus via breath, speech or cough) the virus 83 days after infection, however after 9 days they were deemed to be non-infectious.

Keeping yourself safe if you are just about to fly

There are several things you can do to give yourself the best chance of avoiding exposure to Covid.  Over the last 20 months we’ve grown used to some of them:

  • Hand-washing
  • Wearing a mask
  • Social distancing
  • Avoiding large crowds

However, as the Omicron variant has far more transmissibility, even some of these measures may not be as successful as with previous variants.

Find more information about booking a PCR test or a Lateral Flow Test. You can either visit our clinic in Truro, Cornwall or Plymouth, Devon or take your test at home.