COVID-19 Antibody Test frequently asked questions
- What is the antibody (or serological) test?
- How does an antibody test differ to a virus (swab/PCR) test?
- Can members of the public book an antibody test?
- What do antibody test results mean?
- Can this antibody test tell me if I have an infection now or had a recent infection?
- If you test positive for antibodies, can you ignore lockdown restriction?
- I have a positive antibody result, do I still need to wear personal protective equipment (PPE) with patients?
- I had some respiratory symptoms at the time that I had my antibody test. Could those have been due to Covid-19?
- What does a negative antibody test mean?
- How will I be informed of the result?
- Are there any risks to having the test?
- How will my information be used?
- I was ill earlier this year and had a positive test for the presence of the virus, but I now have a negative antibody test. How can this be?
- A household member was ill earlier this year and had a positive test for the presence of the virus, but I now have a negative antibody test. Does this mean that I was not infected?
- I have never had symptoms of Covid-19 but now I have a positive antibody test. Have I really had the infection?
- I have never had symptoms of Covid-19 but now I have a positive antibody test. What about my family? Have they been infected?
- Can I get my family tested?
COVID-19 antibody testing is a blood test to look at whether the body has produced an immune reaction (antibodies) to the COVID-19 virus. Antibodies develop in viral infections as part of the body’s attempt to fight the virus. An antibody test can tell someone whether they have had the virus that causes COVID-19 in the past. The test works by taking a blood sample and testing for the presence of antibodies to the COVID-19 virus. It takes time for the body to produce this response. The tests we are offering will look for the two antibodies (IgM and IgG) that are produced by the body after infection.
Antibody test: Antibody tests are used to detect antibodies to the virus as a marker of past infection. A positive test result indicates that a person has previously had the virus and has developed some form of immune response.
PCR test/virus test: In contrast, a PCR test aims to find out if you currently have the virus. A positive result does not necessarily indicate that you will go on to develop antibodies to the virus and an immune response. It is possible that around 10% of people who test positive will not develop an immune response.
Patients who are already having blood taken as part of other tests (either in hospital or in their GP practice) may be asked whether they would like an antibody test.
A positive antibody test demonstrates that someone has developed antibodies to the virus. The presence of antibodies signals that the body has staged an immune response to the virus. This usually happens about two weeks after the first symptoms. COVID-19 is a new disease, and our understanding of the body’s immune response to it is limited. We do not know, for example, how long an antibody response lasts, nor whether having antibodies means you can’t transmit the virus to others. Our understanding of the virus will grow with new scientific studies as evidence emerges. An antibody test result can only tell an individual whether or not they have had the virus in the past. Antibody tests are also being used currently in surveillance studies, to understand what proportion of the population has already had the virus.
The test for antibodies is only reliable for detecting that you had the infection more than two weeks ago.
No. There is no evidence yet to suggest that those who have been proven to have had the virus are immune. This is the position of the World Health Organisation. As the presence of antibodies doesn’t not necessarily mean you are immune, you should continue to comply with social distancing measures and government guidelines. All infection prevention and control measures must continue to be in place irrespective of the presence of antibodies.
All Public Health England and infection prevention and control measures must continue to be in place irrespective of the presence of antibodies.
The antibody test should only be used for testing for past infection and we do not advise the test until after 3 weeks following infection. It is more reliable after this time period. However, it will occasionally pick up antibodies earlier in the illness. If you have had recent symptoms (starting less than seven days ago) that you think might be due to Covid-19, please follow “stay at home” advice and discuss this with your line manager. You might still be eligible for a nose/throat swab if your symptoms started less than five days ago.
Symptoms of Covid-19 are:
- new, continuous cough
- high temperature
- loss of, or change in, normal sense of taste or smell (anosmia).
For most people a negative test will mean that they have not had the infection, if the test was done more than two weeks after the start of symptoms. However, not all infected individuals make enough antibodies to be detected by the current tests, so, for a small number of people, a negative result may not mean they have not had the infection, especially if there were no symptoms or very mild symptoms.
Communication of the result is the responsibility of your employing organisation or for patients, the organisation that provided the test. The results will not go on employment record and your GP should be able to access the result if required and according to local information sharing protocols.
There are some risks related to having a blood test, such as feeling dizzy and faint during and after the test but nothing specific to this antibody test. Risks can also include bruising at the venepuncture site. Serious complications such as an infection at the site where blood was taken and phlebitis (swelling of the vein) are possible but generally extremely unlikely.
The anonymised results across the testing programme will provide information on the prevalence of COVID-19 in different regions of the country and help us better understand how the disease spreads.
No test is 100% sensitive. This means that this test might miss some people who have had a previous infection. Sometimes this is because the test has been taken too early. For the antibody test used in our organisation, we know that the test gets even better at picking up antibodies 6 weeks after patients first develop symptoms of Covid-19. The nose and throat swab test (PCR) that is performed for the presence of the virus is very reliable. If you were positive by this test, it is highly likely that you have had the infection.
It is possible that you may have been infected at the same time as the member of your household and the test is not picking up the antibodies (for the reasons that have already been described). It may also be that the infection did not pass on to you, particularly if the infected person self-isolated.
It is now known that as many as 20-50% of people with Covid-19 do not have symptoms; or they have symptoms that are so minor that they do not realise that they have the infection. The antibody test that we are using is very specific, which means that a positive result makes it highly likely that you have indeed had the infection.
It is possible that they may also have been infected, particularly if you did not selfisolate from them, but we cannot be certain without them being tested.
Currently, the test is being offered to NHS staff, participants of research studies, and where clinicians request the test for patients or where patients request the test and are already having a blood test performed for another reason. This may change in the coming weeks.