Coronavirus testing explained
Find out about the three main types of coronavirus testing, how samples are collected, and what the tests can tell us.
There are two main types of coronavirus testing – those that can detect the presence of the virus currently and those that detect a previous response to the virus by your immune system..
Only one test is currently being used widely – the PCR test. This test is used for patients and NHS staff, as well as in the community, and it gives you a fairly accurate indication of whether or not you are infected with coronavirus currently. The antigen test is a different test that can also tell you if you are currently infected, but it is much less accurate than the PCR test and not yet in wide use. The antibody test is still being developed for wider use and its result can indicate that you may have previously had coronavirus.
Most coronavirus samples are currently collected by placing a swab into the nose and/or throat. The swab is then usually sent in a test tube to the lab to be analysed. Some tests are being developed that can be rapidly analysed by machines at the hospital or in another care setting.
Antibody and antigen testing will use a blood sample either from a finger prick test or a standard blood test instead.
The PCR test looks for evidence that the virus is currently in your body, by detecting the presence of its RNA in a swab sample from your nose/throat.
The PCR test detects the genetic material in the virus called RNA. When the sample reaches the lab, a solution known as a ‘reagent’ is added to it. If there is virus present this reagent starts a ‘chain reaction’ and creates billions of copies of the genetic material in the virus so that there is enough that it can be detected and analysed by scientists to provide a positive result.
The test usually takes between 12 and 24 hours to return a result but new technology may be able to provide a result more quickly by using a machine in a hospital or other care setting.
The PCR test can therefore only tell us if the virus is currently present in the body.
This test is also known as an RNA, genetic, molecular, viral detection or swab test. Sometimes PCR tests are also incorrectly referred to as ‘antigen tests’ but these are slightly different. Antigen tests are not widely used for coronavirus testing currently.
The antibody test looks for evidence in a blood sample that your immune system may have responded to the virus already.
The antibody test has been widely covered in the media because it has the potential to tell us a lot about who might have previously been infected with coronavirus. Public Health England have recently approved an antibody test developed by pharmaceutical company, Roche. No date has yet been given for when this type of testing could start.
Different types of antibodies are produced by the immune system in response to ‘foreign’ invaders in the body, such as viruses, and these antibodies stay in the body after the infection has ended. Antibodies are quite specific to the type of virus and can provide immunity against catching the virus again. It is not currently known how long coronavirus antibodies stay in the body.
Research is currently being conducted to examine coronavirus antibodies in more detail. This will help us to understand whether having the infection once reduces our risk of contracting it again in the future.
The antibody test detects the presence of the antibodies that are produced as a result of the body’s response to coronavirus. The analysis of the sample is done by adding synthetic antigens from the coronavirus to the blood sample, to see whether they bind together. If antibodies are present, that suggests that you may have previously been exposed to or infected with coronavirus.
Unlike the PCR and antigen tests, the antibody test is not used to detect if you are currently infected with coronavirus. It is used to identify a possible infection previously that has triggered a response from your immune system, leaving antibodies behind in the blood.
This test is also known as serology.
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