Lateral Flow or PCR? Which test is right when?


There has been a lot of confusion about covid tests in recent months. With the rules around testing changing frequently as the country opens up it can be hard to keep up, but one thing hasn't changed which is that we have two different tests for covid and that they have very different purposes.


With the government placing so much emphasis on people testing themselves at home and the fact that both types of test can be done at home, it is very easy to get confused, and many people are doing a test, thinking they have ruled out covid as a cause for their symptoms, when in fact they have done the wrong test. It's a very easy mistake to make and we thought it might be helpful to go over the difference in the tests.


The PCR Test

This is the original test that first became available in the community about 6 months into the pandemic. It is booked through the government website or by phoning 119 and is either done at a test centre (our main one has been at Surrey Sports Park) or the NHS can send you an individual test which you take yourself and then send away for the sample to be analysed. The PCR test is the most reliable test we have. This means that (although no test is 100%) it is extremely likely to be correct - if the test is negative then you can be confident that you don't have covid at the time of the test (obviously if symptoms develop then this could change). This test is therefore the one we should arrange if we have symptoms - such as a new, persistent cough, a fever or a loss of the sense of taste or smell. PCR tests are also sometimes required for travel to other countries or on return from another country, and are required if you live with someone who develops covid.


The Lateral Flow Test

These tests became available much later, in the first half of 2021, and many were originally provided by employers, especially schools and health or social care settings. Now anyone can order these from the government. The key thing about lateral flow tests is that, while they are helpful, they are not as reliable as a PCR test. The main difference if that they will miss covid about 30% of the time - that means that if you have a negative lateral flow test you could still have covid. The purpose of lateral flow tests, therefore, is not to see if someone with symptoms has covid, but to try to pick up people who have covid but no symptoms. The thinking behind this is that such people won't be getting a PCR test, and that even if the lateral flow test sometimes misses that they have covid, at least some people who have the virus without symptoms can be picked up this way and that will allow them to self-isolate until they are no longer contagious. Lateral flow tests are therefore used when the true likelihood of covid is low (because the person does not have symptoms) but in order to try to catch some of the people who might otherwise spread the infection. Some employers therefore ask their employees to test themselves regularly, people should do lateral flow tests if they have had contact with someone outside of their household, and some events may ask people who have not had 2 doses of the vaccine to perform a lateral flow test before attending.


The key message in all of this is simply: If you have symptoms then please get a PCR test.

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