Which Type of Test is Best for Covid-19?

The UK has seen over 22 million cases of coronavirus since the beginning of the coronavirus pandemic in 2020 with cases moving up and down on an almost daily basis. Government policy has followed many changes in accordance to the different strains that have developed and as the trajectory of the virus has changed.

Since the initiation of the coronavirus pandemic over two years ago, we feel that we have become experts on coronavirus tests – where to obtain them, how to administer them, how to decipher the results, and what it means if we test positive.

PCR and rapid antigen tests (also known as lateral flow tests) have been used more or less interchangeably, but what are the differences between them? Is one better than the other? Here we discuss the different types of covid-19 tests and their potential advantages and disadvantages.

What is the difference between an antigen test and a PCR test?

Antigen tests and PCR tests are both designed for people who are wanting to confirm the presence of coronavirus. Both tests are commonly accepted as a reliable means of testing for coronavirus.

It has been suggested that antigen tests have a slightly lower sensitivity than the PCR test but generally speaking this will depend on the company used.

Samuel Davies of Kallyss.com commented: “Covid tests for many have over the last few years proven to be very expensive and therefore, having a greater variety and thus greater competition in the market is no bad thing as it reduces the need to borrow money online or from family and friends, helping more people stay out of debt wherever possible. Much like any other industry, the more competition that exists, the better this is for customers and consumers.”

What are rapid antigen covid tests?

Rapid antigen tests, also known as lateral flow tests, are qualitative in vitro diagnostic tests designed to test the presence of coronavirus (SARS-CoV-2 virus) proteins. You can use them for early detection of the virus and you administer them by taking a nasopharyngeal sample (via the nostril). These tests can confirm the infection both in patients who have symptoms and those who do not. They can also be used as a way of verifying false negative results obtained in a PCR test.

In general, rapid antigen tests have a high accuracy rate with an average sensitivity of around 93% and a specificity of more than 99%, but this will depend on the exact test used.

What is a PCR test?

A PCR test, or polymerase chain reaction test, is a molecular test that detects the presence of genetic material of SARS-CoV-2 (the virus that causes Covid-19. It analyses your upper respiratory specimen in order to detect the virus.

Are rapid antigen covid tests the most accurate?

It is generally considered that antigen tests are a reliable way of testing for coronavirus and that they have a high sensitivity and specificity. They are considered to be especially reliable in people who are actively contagious or when they are taken during the initial days after the onset of symptoms.

However, experts say that if you test negative on a rapid antigen test it should not be used as a guarantee that you cannot spread coronavirus; only that the chances are lower. Antigen tests work better when the viral load is at its highest so are less reliable either in the very early or very late stages of the infection.

There is some research which suggests that antigen tests are unable to detect coronavirus until at least two days after exposure to the virus, with an average window of three days before the individual tests positive. So, for the best result, individuals should wait to take an antigen test until a couple of days after exposure to the virus.

A spokesperson from GlobMed.co.uk said: “Covid 19 can be a serious illness for those who are immunocompromised or otherwise vulnerable. Therefore, always follow the advice of your doctor or local health authority who will be best place to advise what type of test is best for you in your circumstances.”

What is the difference between antigen tests and PCR?

At the most basic level, rapid antigen tests are used to detect antigens found on the surface of the virus; PCR tests, on the other hand, look for the presence of viral genetic material.

Both antigen tests and PCR tests are thought to be reliable ways to test for the presence of coronavirus. Each comes with their own benefits and disadvantages.

For example, antigen tests are thought to be better than PCR tests for the following reasons:

• Faster – rapid antigen test can typically be performed and give results within 15-30 minutes which is significantly faster than with a PCR test which can take a couple of days to be processed
• Cheaper – rapid antigen tests are considerably cheaper than PCR test
• Simpler – unlike PCR tests, rapid antigen tests do not require qualified personnel or additional machinery in order to process the results of the test

However, PCR tests are said to be more reliable and accurate due to the testing methodology; they test the specific genetic material of the virus which means that they are able to eliminate interference from other viruses.