How accurate is the Covid-19 antigen test?

December 27, 2021
Written by
Edward Heywood
How accurate is the Covid-19 antigen test?

Several Covid-19tests are available via public and private services today. And chances are, you’ve got some questions.

Should you be taking a PCR test? Or a Covid-19 antigen test? What do these tests look for? And how accurate is a Covid-19 antigen test anyway?

This guide will set the record straight. We’ll discuss what a Covid-19 antigen test involves and how it differs from a PCR test. Then we’ll compare antigen test accuracy rates with PCR tests — available through both the NHS and private clinics.

The Covid-19 antigen test

The Covid-19 antigen swab confirms if you are infected with coronavirus at the time of testing. It’s only available at private clinics and not on the NHS.

If you test positive, you had the virus at the time the sample was taken and you need to self-isolate in line with government guidelines. We’d recommend taking a PCR test too, to confirm your result.

If your antigen test comes back negative, you didn’t have the virus at the time the sample was taken and can carry on with your daily activities as (new) normal.

How is the Covid-19 antigen test done?

If you book a Covid-19 antigen test, a swab will be taken from your nose. At-home kits aren’t currently available. You’ll need to attend a private clinic so a medical professional can take the sample for you.

Your sample is then tested for proteins associated with Covid-19. The results are available quickly — often within hours.

How does the Covid-19 antigen test differ from the PCR test?

The Covid-19 antigen test and the PCR test are often confused with each other.

The NHS only offers PCR tests. But both antigen tests and PCR tests are available if you go private. Both tests tell you if you currently have coronavirus, but they are different tests, looking for the virus in different ways:

  • Antigen tests look for proteins associated with Covid-19
  • PCR tests look for genetic material associated with Covid-19

PCR tests use a sample taken from both the nose and throat. And they are seen as the more reliable option, as we’ll explore below.

How accurate is the Covid-19 antigen test?

Antigen tests are faster, cheaper but less accurate than PCR tests. At Corona Test Centre, our Antigen tests give accurate results in 93.8% of cases.

A PCR test takes longer to process, is more expensive to book, but it is more accurate as a result. A Corona Test Centre PCR test provides 99.9% accuracy.

Why is the PCR test more accurate than the Antigen?

When a PCR sample is tested it goes through a process called amplification. This basically means that even if only a tiny sample of Covid-19 is present, it will still be detected.

Antigen testing doesn’t involve this same process of amplification. This means that some positive cases will be missed, especially when people are asymptomatic and aren’t producing lots of nasal discharge.

As a whole, there are more false positives and false negatives associated with antigen testing than with PCR testing.

As mentioned, at Corona Test Centre we recommend that any positive antigen test result is followed up with a confirmatory PCR test. The more accurate test will confirm your result and ensure you’re not left in self-isolation when you’re actually free of the virus. This is already common practice in a number of countries around the world.

Nevertheless, antigen testing is still a useful tool to have at our disposal. It offers fast “screening” results — a quick and cost effective way to be almost sure when someone has the virus or not.

Key benefits of the Covid-19 antigen test: Cost-effective option, providing fast results.

Key benefits of the PCR test: The most accurate test available for finding out whether you have Covid-19 right now. You’ll just have to wait a little longer for results.

NHS PCR tests — less accurate on the whole?

On the topic of accuracy, it’s worth noting that the PCR tests you get through the NHS, and the PCR tests you can get through private clinics, differ significantly.

NHS PCR tests

The Covid-19 PCR test is the test you’ll get if you go to an NHS test site or have an NHS test sent out to your home.

Scientists at the University of Bristol say that NHS PCR tests are accurate around 80% of the time. According to the NHS, the figure is closer to 70%. That means, in 20-30% of cases, someone will test negative even though they are currently infected with Covid-19.

So why does this happen? The test itself is very accurate. But there are often problems with the way it is administered.

Sometimes the swab sample isn’t good enough; most of the NHS tests are self-administered by patients themselves. Also, sometimes a patient is tested at the wrong stage of infection. After a week of infection, the virus can be present in the lungs but is no longer present in the nose. This can lead to false negatives.

PCR tests from private clinics

Private PCR tests tend to offer greater accuracy and therefore greater peace of mind and safety, too. You can attend a clinic where a medical professional will conduct the test for you. This means you can be sure that a good sample has been taken.

Which test should you choose?

Both Covid-19 antigen tests and PCR tests are available at Corona Test Centre. You can choose either option if you want to know whether you’re currently infected with Covid-19. Please note that we cannot accept anyone who is currently demonstrating symptoms.

The test you pick will depend upon how quickly you need the results and how much you want to spend.

  • Antigen test results are available the same day you take your test. Prices start at £120.
  • PCR test results are available within 24 to 48 hours. Prices start at £165.

All tests are conducted by medical professionals in our London-based clinics. And we guarantee good appointment availability.

If you’re ready to book your test, head to our online portal. Here you can choose from our range of test centres and pick a time to suit you.

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