What is the Difference Between Lateral Flow and PCR Tests?

There are a variety of different forms of testing for coronavirus that you can access in the UK. It is important to understand them, as the method of each can vary and depending on why you are getting tested, the type can vary also. In the UK, the two main tests are PCR tests (polymerase chain reaction) and LFD tests (rapid lateral flow). Both require a swab to be taken from the person being tested, but they are looking for different things. As of October 2021, day 2 LFD tests are a travel requirement.

PCR Tests

PCR tests are the tests that have been the most widely used by the NHS during the pandemic. When doing them, you take a swab of the back of your throat and the inside of your nose using a cotton bud. Why? So that a sample of RNA, otherwise known as ribonucleic acid, can be collected. These samples carry the virus generic code that is vital for getting your results.

Once you’ve done this, it is sent to a laboratory where it is analysed. During this analysis, the sample will be cooled and heated so that the RNA multiplies. Scientists will be able to determine whether the virus is present in the samples. PCR test results can vary, usually they can be given the day following the test, or sometimes take up to 3 days to come back.

PCR tests differ from LFD tests because they are mainly for people with COVID symptoms. According to the NHS, you should get a PCR test as soon as possible if you have any main symptoms of coronavirus such as a cough, high fever temperatures, or changes to either or both of your senses of smell and taste. You are required to stay at home, and only leave to get tested. You must return home afterwards and wait for the result.

If you have been a close contact to someone who has tested positive for COVID, you will be required to take a PCR test, even if you haven’t begun to develop noticeable symptoms.

Lateral Flow Tests

Unlike PCR tests, lateral flows aren’t sent to a laboratory for analysis, and are a quicker way to gain simple results. You might be thinking, why do people even need to take a PCR test?

Lateral flows are different because they detect proteins, otherwise known as antigens, that exist in a person with the virus. Like a pregnancy test (which they also superficially resemble) LFD tests can be carried out at home.

For an LFD, you take a sample using a swab from the back of your throat and your nose. This time, unlike a PCR, you dip the swab into an extraction solution and drip the solution onto an absorbent pad. This is where you can read your results. The pad will change colour if COVID antigens are present in your sample. The result will be visible 30 minutes after applying the sample.

A line at the top of the strip saying ‘C’ will appear if the result is negative. Two lines, one by the ‘C’ and ‘T’ letters means your result is positive. If there is a single line by ‘T’, it means there was a void reading, and the test was not executed properly.

Although quicker than a PCR test, LFDs are known for only detecting 77% of positive cases, making them a lot less accurate. LFDs are distributed to those without known symptoms and in the UK, can be used for travel purposes or can be used routinely by those whose jobs put them at risk of catching and spreading the disease (such as medical professionals or carers).

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