Types of tests
These are the two main types of tests for COVID-19:
- PCR (polymerase chain reaction) testing – a swab test to confirm if you have the virus.
- Antibody (serology) testing – a test to detect if you’ve had the virus and have developed antibodies.
What is PCR swab testing?
PCR testing works by taking a swab of your nasal passage and/or back of your throat. The swab is then sent to a laboratory to be analysed for genetic material specific to the SARS-CoV-2 virus (the virus that causes COVID-19). This test currently forms the basis of reported case numbers in the UK.
What do PCR testing results show?
PCR testing only tests for current infection. This is important – it can’t tell you if you’ve already had COVID-19 or if you have immunity to it.
How long does it take to get the results?
It can take a few days to receive your result from a laboratory-based test. Outside of the UK, some rapid point-of-care PCR tests have been developed. These have the potential to be performed in a clinical setting and provide results in as little as five minutes.
Are there any limitations?
As with any test, there are limitations to PCR swab testing. Although a positive test is very accurate for confirming if you have the disease, a negative test does not rule out current infection. Research has suggested that initial results may be positive in as few as six out of every 10 people infected with COVID-19. Correctly timing when swabs are taken is essential to maximise accuracy. Public Health England currently recommends completing a PCR swab within three days of symptoms developing to maximise accuracy.
What is antibody (serology) testing?
Some antibody tests have recently been approved for use by the UK government. Antibody testing is a test to find out if you’ve previously had the virus and have developed antibodies. When you have an infection, your body responds by producing antibodies to defend against the virus, should you come into contact with it again. Because COVID-19 is a new virus, scientists don’t yet fully understand the antibody response in humans.
How soon do antibodies develop?
Research has suggested that antibodies may become detectable from eight to 10 days after symptoms develop. However, antibody tests for other viruses (e.g. HIV) are normally tested for from 21 to 28 days after the date of suspected infection. In theory, antibody tests can be used for indicating previous infection with COVID-19, including those who only experienced mild, if any, symptoms. But the timing of such a test is crucial for an accurate result.
What does the test involve?
There are two forms of antibody tests that have been developed:
- Laboratory-based tests
- Rapid, point-of-care tests
Both involve taking a blood sample, though some require only a finger-prick. Some rapid tests give a result in as little as 10 minutes. It’s important to note that no point-of-care tests have been approved for home use in the UK.
Are there limitations?
Although there is excitement about the potential of widespread antibody testing, there are limitations.
- It’s not yet known how long the body maintains an immune response to COVID-19. In some viruses, immunity lasts a lifetime, whereas in others immunity lasts for months.
- We don’t yet know if the antibody response detected is the type required to protect you from future infection.
Does the antibody test show if you’re immune to COVID-19?
No. The UK government and the World Health Organization agree there is currently no evidence that someone with antibodies to COVID-19 won’t catch the virus again in the future.
With this in mind, it would not currently be appropriate to use an antibody test as the sole marker for safe return to work. However, accurate antibody tests may give public health authorities and the government a better idea of how many people have previously been infected with coronavirus.
Who can have a test?
PCR testing is being provided through the NHS, with people in hospital and essential workers getting priority. But anyone over the age of five with symptoms of coronavirus can now request the test online through the NHS website. Some private providers are offering PCR testing, and some private providers are offering antibody testing. The situation with testing is changing rapidly and there are plans to keep making testing more widely available.