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COVID-19 antibody tests: how do they work and who can get tested?
Testing is key to bringing the UK out of the pandemic and out of lockdown. As an antibody test is finally approved by Public Health England and made available for NHS and care home staff, some NHS patients and private booking, what do you need to know about it?
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What is antibody testing?
There are two types of test for coronavirus:
- A PCR swab test to find out whether you currently have coronavirus.
- An antibody blood test to find out whether you have previously had coronavirus and may have some degree of immunity.
The PCR test is available to people of any age in England and Wales with symptoms of coronavirus, or anyone in Scotland or Northern Ireland over 5 years of age with symptoms of coronavirus. It involves a swab of the nose and throat. If you have symptoms of coronavirus, you and anyone you live with should self-isolate and book a test via the NHS website.
Priority PCR swab testing through GOV.UK is available to people with symptoms if they:
- Are an essential worker (across the UK).
- Are over 5 years old and live with an essential worker (across the UK).
- Are under 5 years old and live with an essential worker (England and Wales only) - this test needs to be carried out by a parent or guardian.
The antibody test involves a blood test to find out if someone has antibodies which indicate that they have had COVID-19 in the past. When the body becomes infected, it produces antibodies to fight the infection. Therefore, if the antibodies are present in the blood, it indicates that an individual has had COVID-19.
Antibody testing is important as it will tell us how many people have had COVID-19. Not everyone who has had symptoms has been tested and not everyone who has had coronavirus has had symptoms. It's impossible to know the true number of cases, spread and actual death rate of the virus until an antibody testing service is made available to everyone.
To some people, the tests are also considered a key component in bringing the UK out of lockdown, although this is controversial. Knowing who has and has not had the virus is critical in determining areas which have been more or less badly affected and planning the next steps in managing the pandemic.
However, some have suggested that those who have had the virus, who may have some immunity, should have 'immunity passports' and be allowed to go back to work.
The World Health Organization has already advised against doing so as there is a lack of evidence that these would be beneficial, and could do more harm than good. There are also important question marks over what having antibodies means, which we discuss later in this article.
How does the antibody test work?
Initially, the antibody test was planned to be a pregnancy-style home test kit using a drop of blood on a stick (rather than urine on a stick). However, none of the tests of this type proved to be accurate enough. As a result, the tests which have been approved by Public Health England (PHE) do not work like this. Instead they involve blood being taken by a healthcare professional such as a pharmacist, phlebotomist, nurse or doctor and sent to a lab to be tested.
Antibody testing is not yet available through the NHS in the same way as PCR swab testing. It's initially being rolled out to NHS and other essential workers but this will likely be extended in the coming weeks and months. Those who aren't eligible for a free test will, in the near future, be able to be tested privately at pharmacies. Coming soon, you will be able to book an antibody test online with a pharmacist at a time that suits you through Patient Access.
Previously there were a whole host of problems when it came to antibody testing. Early on in the pandemic, the UK government spent a reported £16 million on millions of tests which all later failed to meet accuracy criteria when they were tested in UK laboratories. However, the new tests do meet the requirements to be able to be offered to the public.
The only antibody tests currently approved by PHE are the Roche and Abbott antibody tests. The results of other tests on the market cannot be trusted as they do not meet the same standards as the Roche and Abbott tests. This also applies to home testing kits which were previously available.
In people who had been infected by coronavirus, the Roche and Abbott tests were found to give an accurate result 100% of the time. In people who hadn't been infected, the results were accurate more than 99.7% of the time. This means that if 1,000 healthy people were tested, only two would be told that they had had coronavirus when they hadn't. This is far lower than with previous tests.
The new tests can be trusted to give an accurate result as they have been fully validated and tested by PHE. The tests will be carried out by a pharmacist or other healthcare professional so you can be sure that they'll be taken accurately and handled safely.
Home vs healthcare professional testing
There are two ways to take the blood sample needed to test for antibodies. The first is a standard blood sample, where a needle is inserted into a vein and a sample taken into a bottle which is sent off. Tests using blood taken in this way have been approved by PHE.
The other way of taking blood involves a fingerprick sample of capillary blood, collected in a small container. On 29th May, The Medicines and Healthcare products Regulatory Agency (MHRA) asked all suppliers to stop providing tests using these samples until they had checked to see whether results using this type of blood sample were accurate.
Until we have an update, the MHRA also recommends that anyone who has carried out a home fingerprick test should not consider the result to be reliable.
What does it mean if you test positive?
Within a couple of days of taking the test, you'll be notified of your results. There are three possible results after taking an antibody test: positive, negative or indeterminate (borderline).
Immune or not?
A positive result means that COVID-19 antibodies have been found in your blood, which indicates that you have previously been infected by coronavirus. This does not mean that you are immune to coronavirus.
Scientists still don't know just how much immunity you gain from a COVID-19 infection so even if you test positive, it's possible that you could be infected a second time or carry the virus to infect others. You still need to follow the social distancing and hygiene measures set out by the government, even if you've previously had the virus.
It is also important to realise that even if doctors do discover in future that having antibodies confers immunity, it is not known how long this immunity lasts for. Immunity to other forms of coronavirus appears to wane quickly. In one study involving a coronavirus which causes the common cold, some people exposed to the virus a year after developing antibodies were re-infected, although none developed symptoms of a cold.
If the test gives you a negative result, it means that you don't have the antibodies to indicate that you have had coronavirus so you haven't had COVID-19.
You can also have an indeterminate result, meaning that the test can't confirm either a positive or negative result. You may be asked to take the test again in a couple of weeks' time.
Whatever your result, it's equally important that you behave sensibly, follow the official guidelines and protect yourself and others from the virus just as you would have before the test.