I’ve had a few tests for Covid. They’re uncomfortable, but you do get used to it. Luckily all my tests have been negative.

The most frequently used test is a lateral flow test which can provide a result in under an hour. While they are not 100 per cent accurate, they should not produce any false positives, but can produce false negatives if someone only has a small amount of the Covid virus.

Low false positives make them reliable enough for mass testing. But how does the test work?

A Covid lateral flow test works in the same way as a pregnancy testing kit. It detects specific proteins and provides a visible line when these proteins are detected.

The Covid virus is essentially made up of proteins and these are detected by antibodies. When you swab the back of your throat and nose you are trying to collect any virus that could be sitting in those areas.

The swab is dipped in a solution and this solution is applied to a strip of filter paper in a rectangular plastic cassette.

The strip is preloaded with antibodies bound to nanoparticles of gold; particles so small they can’t be seen with the naked eye or a microscope.

The antibodies recognise proteins specific only to the Covid virus.

The solution flows across the filter paper, hence lateral flow, where it passes through a test zone which has a concentration of gold nanoparticle antibodies.

If any Covid proteins are present, they get trapped in this zone and it appears as a pink line.

It’s pink because gold nanoparticles are pink in colour. In a pregnancy test, latex is used instead of gold and this produces a blue line.

Further along the strip of filter paper is another zone loaded with chemicals that recognise the antibodies attached to the gold particles.

This produces a second pink line which confirms that the test worked, that is, antibodies in the first test zone were picked up and carried across the filter paper.

When a tester looks at the completed test, if they see two pink lines it means that the test is positive, you have Covid.

If the second pink line shows, but not the first one, it means the test worked but your test is negative.

If there are no pink lines, it means the test did not work and you will have to do another test.

The test is very specific – it only detects Covid so it would not give a positive result if you had a cold or flu.

However, you do need to have enough Covid virus particles to make the test show positive. This is why people are asked to take two tests a few days apart.

If you have just picked up the virus it takes up to five days for it to replicate and for your body to react and start to show symptoms.

The test is not infallible as it can miss people who have very low levels of the virus.

The failure to detect low levels of Covid viruses in a person is one of the main drawbacks of the lateral flow test. This is why it’s so important not to rely on a negative test and abandon social distancing or hand sanitising. What the test does is enable people with high levels of the virus to isolate and that helps prevent the virus from spreading.

A more accurate Covid test is a PCR test. This works in a very different way. PCR stands for polymerase chain reaction. Polymerase is a natural enzyme we all have in our body; it’s involved in making new cells by cell division, helping our DNA to replicate. What the PCR test does is replicate the genetic material found only in the covid virus, literally increasing the amount of Covid genetic material so that it can be detected.

The crucial bit is that the test only replicates Covid genetic material.

It takes time and specialist equipment for the enzyme to create the genetic material, so the test is not quick and takes up to 48 hours.

That said, it does give us an idea of how much virus a person has, the viral load.

The faster we reach the threshold for detecting the virus the more virus there was to begin with. If it takes a long time, we know there was very little virus initially.

The lateral flow test is used if you have no Covid symptoms, but if you have a test because you have symptoms, then it is likely you’ll be given the PCR test.

Until we reach herd immunity through vaccination, tests are here to stay.

At present they are crucial in understanding how well we are doing reducing Covid cases.