Antibody tests: How do they work and should I get one?

29th May, 2020 • 6 min read

Testing people for the coronavirus is vital if the outbreak is to be brought under control. Doing so helps authorities get a picture of where the virus is or has been spreading.

Some tests, like taking a swab from a person’s nose or throat, identify when a person has an active coronavirus infection. These tests help identify who should self-isolate to protect others.

Other tests, like coronavirus antibody tests, can identify if a person has had the virus and recovered. And it’s these tests that media reports currently suggest could help to pinpoint who may be able to come out of lockdown safely.

However, as new tests, there are many questions surrounding how well they work, and their benefits and limitations.

If you’ve read about coronavirus antibody tests and are interested in taking one, here’s what you need to know.

What is a coronavirus antibody test?

When a virus or any other bug infects you, your immune system develops antibodies to fight the infection. These antibodies stay in your blood, which means that they can be detected in blood samples taken after an infection.

Coronavirus antibody tests look for antibodies against the virus in your blood. However, they don’t look for the virus itself and so aren’t used to find out if you’re currently infected with the coronavirus. They simply tell you if you’ve been infected in the past.

Why are antibody tests useful?

A key goal behind using antibody tests is to identify who has already been infected and can come out of lockdown safely.

According to the World Health Organization (WHO), some governments are considering using a positive coronavirus antibody test as the basis for an “immunity passport” or “risk-free certificate” -- confirmation that a person is safe to travel or to return to work, under the assumption that they’re protected against re-infection.

The UK government is considering this approach, for example.

However, there’s currently no evidence to suggest that this assumption is true. In fact, the WHO and the US Centers for Disease Control and Prevention maintain that it’s still unclear if people with coronavirus antibodies are protected from a second infection.

How are antibody tests done?

The tests use blood samples taken by health professionals which are then analysed for antibodies. Blood samples may either be taken from a vein in your arm or a finger prick.

As you only need a drop of blood to look for antibodies, companies have been developing finger-prick tests for you to use at home and send your samples to a laboratory.

Tests that provide an instant result at home are also being developed.

How accurate are antibody tests?

The accuracy is these tests come down to two factors: sensitivity and specificity.

The sensitivity describes how good a test is at correctly identifying people who really have had coronavirus and have the antibodies in their blood. This makes a negative test more reliable.

The specificity is how good a test is at correctly identifying people who don’t have any antibodies. This makes a positive test more reliable.

Both factors are presented as percentages by the companies that make them and research teams that have tested them, with many now having sensitivities and specificities over 99% and of 100%.

Should I get an antibody test?

Right now, the only real benefit of getting an antibody test is knowing that you may have had the virus.

While you may find it helpful or reassuring to know this, it’s important to note that whether you test positive or negative for coronavirus, you’ll still need to take care to protect yourself from it.

What do the test results tell me?

A positive test means you’ve had the infection, but there’s still a chance that you could catch it again or pass it on to others.

And a negative test suggests that you either have a current infection that you haven’t produced an immune response to, or you may not have had coronavirus at all.

All of these options suggest that you’re still at risk of catching and/or spreading the virus regardless of your test result and, as such, you need to continue

taking precautions
, like washing your hands often and avoiding close contact with others.

What are the limitations?

Testing positive for antibodies against the coronavirus doesn’t mean you’re immune to future infections -- researchers and health agencies still don’t know enough about how the virus infects people.

Testing negative also doesn’t necessarily mean you’re not infected, as antibodies can take between 1 and 3 weeks to show up.

Some tests are also not specific to coronavirus antibodies.

Where can I get an antibody test?

Antibody tests are generally available through healthcare providers and laboratories.

Home tests are available to buy in stores and online in some countries, including ones in the UK by blood testing service Thriva, sexual health service Better2Know, and other private clinics.

However, the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK has now called for a temporary pause on the use of home tests while it carries out a national review to check how reliable these home tests are.

“Use of unvalidated sample types may lead to unreliable results and as such we are working closely with the service providers, laboratories and test manufacturers to resolve the regulatory and patient safety issues,” said Graeme Tunbridge, Director of Devices at the MHRA. “It is in the interests of everyone for antibody tests to be as reliable and meaningful as they can be.”

In the US, commercially available tests need to be approved for use by the Food and Drugs Administration (FDA). But only a handful of home kits have been approved, including one by diagnostic company Euroimmun and another by Abbott laboratories.

However, you can only get these tests through doctors, hospitals or clinics. Some health regulatory bodies are advising against their use until there’s more evidence to show they are truly effective and accurate when used at home by the general public.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.