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Testing for coronavirus

23:00 22 Apr 2020

We explain the different types of tests for coronavirus and why people shouldn’t try and test themselves with online ‘home testing kits’.

Certain people now take priority for testing in the UK. These include hospitalised patients with severe respiratory infections; key workers and members of their households; symptomatic healthcare staff including those with mild symptoms; cases with acute respiratory infections in hospital or long-term care facilities.

Also included are patients with acute respiratory infections or influenza-like illness in certain outpatient clinics or hospitals and elderly people with underlying chronic medical conditions. Such as; lung disease, cancer, heart failure, cerebrovascular disease, renal disease, liver disease, diabetes, and immunocompromising conditions.

There are two types of tests for Covid-19.

The first is an antigen test that looks for the presence of the active virus in your system – antigens are found on the surface of invading pathogens, including coronavirus. Testing for antigens can detect whether someone is currently carrying the virus and is actively infectious.

What happens during antigen testing?

The antigen test for the presence of Covid-19 must be done by medical staff and sent to a fully equipped and accredited laboratory. The length of time can vary between regions but it’s a process that can range from six hours to a number of days.

  1. Sample taken and sent to a lab - A swab (like a large cotton bud) is taken from deep at the back of the throat or nose. This is sent to a virology laboratory. Currently in the UK these are being done in hospitals, care homes, other healthcare settings and some drive-thru facilities (you need an NHS referral to get one) carried out by trained healthcare staff.
  2. The sample is analysed - Most labs used a method called real time polymerase chain reaction (PCR) testing to see whether COVID-19 is present.
  3. Results - This is prepared by a biomedical scientist and as the time varies for getting results, it can range from six hours to a number of days.

What about antibody tests?

The other type of test for Covid-19 is an antibody test that detects whether the virus has been present and the body has responded by creating its own immunity, represented by what is known as antibodies in the blood.

It is believed that if you have antibodies against Covid-19 in your blood, you will be immune to it. This is not yet proven however, given that the initial outbreak only began four months ago.

But this test has been more complicated to create and authorities are not 100% certain that having antibodies means you can’t be re-infected. Whilst there is optimism that those with antibodies will have some sort of sustained immunity for at least the ensuing months to a year, it is still only an assumption.

Do be aware though, that Professor John Newton, the UK’s testing Chief, has warned that none of the antibody tests examined by his team have been able to identify immunity accurately unless those tested had been severely ill. As such, there isn’t certainty that having antibodies means you can’t be re-infected.

The Institute for Biomedical Sciences has also issued a warning about the reliability of the antibody tests currently available.

At least one in ten people who test positive on the antibody test (and are therefore considered to have immunity) will be ‘false positives’ and will not actually have immunity. Another reason why the reliability of tests is of utmost importance and testing of the antibody tests continues.

Public Health England (PHE) advise the public to avoid ‘rapid, at-home coronavirus tests’ because there is ‘little information’ on their accuracy or their ‘suitability for diagnosing Covid-19 infection in a community setting’.

What should I do next?
Should you test yourself if you are worried? No, say experts. It could be a complete waste of time and the test may not even be reliable.

Reviewed by: Hemal Shah, Lead GP, Livi

Last updated:

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