Should I get a COVID-19 antibody test?

We have received a lot of questions about COVID-19 antibody tests and whether you should use these to see if you have responded to the COVID-19 vaccine. In this article, our Patient Advocacy Manager, Charlotte, explains what a COVID-19 antibody test does and why you should be cautious in how you interpret any results.

Before you read the full article here are some key points:

  • COVID-19 antibody tests are not the same as the PCR or lateral flow tests. PCR and lateral flow tests tell you if you have COVID-19 at the time you take the test; antibody tests tell you if you have antibodies from past infection/vaccination.
  • There are many antibody tests that you can buy, but they vary in their quality
  • To tell whether your positive result are antibodies made from the vaccination or ones you made as a result of previous COVID-19 infection, you need to test for the right type of antibodies. You may have had COVID -19 and not known.
  • An antibody test does not tell you whether other parts of your immune system, such as T cells, have responded to the vaccine. Therefore, a negative result does not tell the whole story
  • You are also protected by everybody else being vaccinated and are unlikely to catch COVID-19 while cases are low, especially if you continue to take precautions
  • If you are concerned about whether you are still at risk of COVID-19, such as whether you should return to work, discuss this with your clinical team.

It’s fair to say that the pandemic has been a rollercoaster ride for the blood cancer community. From the moment the list of the clinically extremely vulnerable was announced in March 2020, those diagnosed with blood cancers have had to contend with shielding. Many of you have told us that shielding was really tough, which is why we were all very excited to hear about the approval of the first vaccine, the Pfizer BioNTech one, just before Christmas last year.

However, since then, there have been some initial concerns that the COVID-19 vaccines are not as effective for blood cancer patients as they are for people who are otherwise healthy. In some ways, this makes sense – vaccines rely on an immune system within your body to respond, this is how they work. Most blood cancers are illnesses of the immune system; this is why being at increased risk from infection is a common side effect of leukaemia and experiencing more frequent infections is a common symptom prior to diagnosis.

We know the discussion about vaccines being less effective is worrying and scary for many. However, all hope is not lost; most reports about the vaccine being less effective focus on a lack of antibodies produced. Yet there is more to the immune system than just antibodies and so there still be a response to the vaccine in blood cancer patients. More research is ongoing into the effectiveness of the vaccine on blood cancer patients. This sort of work will take time to do, even with the increased time and effort that is being put in at present. I recommend you sign up to our newsletter, where we will send out our latest information on this when it comes along.

“But what should I do in the meantime?”, I hear you ask. Many of you have come to us to ask whether an antibody test, to see if you have produced antibodies to the vaccine, are appropriate. You may want to be sure you are protected before you return to work, Antibody tests are designed to test whether you have antibodies as a result of having been exposed to COVID-19 in the past (which is different to PCR tests and lateral flow tests, which test for active COVID-19 infection in the body). And it sounds sensible, to simply test yourself after you have had a vaccine, to see if you have antibodies and are therefore protected.

NOTE: as of the 29th of May, the Medicines and Healthcare Regulatory Agency (MHRA) has temporarily requested that companies stop selling fingertip capillary blood sample antibody tests (those that test blood from pricking your finger), as more work is needed to determine if these are as accurate as other types of tests. You should not take these types of tests until the guidance changes. If you choose to pay for a test, you need to choose one where a full blood sample is taken using a needle.

Unfortunately, interpreting a result from a COVID-19 antibody test may not be that easy. Here are some points to remember before you get one:

A negative result does not mean you necessarily have no protection

An antibody test can only test for what they say on the tin, for antibodies themselves. This means you may have a different kind of immune reaction (such as activation of your T cells) that is still providing some protection. You would need a lot more detailed tests to find out what else has happened in your immune system, and these are not tests that are possible to do outside a research study. The immune response to COVID-19 is not well understood because it is still such a new virus in the time frame of scientific study. The immune response of leukaemia patients is even less well understood, as many were protected from infection, thanks to shielding.

An antibody test only tests for certain antibodies, not every possible one

The tests can also only test for the antibodies that bind to the proteins chosen to make the test. You could think about this a bit like Cinderella’s slipper form the classic fairytale. The tests are made from certain “feet” or proteins from the COVID-19 virus, different tests may use different proteins but they vary rarely use the whole virus. Your antibodies are like the “slippers”, in that they only bind to certain proteins. If you have made slightly different antibodies in your body that respond to a protein on COVID-19 but not a protein that is in the test, it might not detect those antibodies. The antibodies are there, and they work, but the test was not sensitive enough to pick them up.

A positive result does not automatically mean you are protected

Another reason why a positive result might give false reassurance is because your antibodies may not be as a result of the vaccine at all. You need more than one test to tell the difference between vaccine made antibodies and antibodies that have formed due to natural infection with COVID-19. You may have had a mild case of COVID-19 and not noticed yet formed antibodies. Naturally formed antibodies, especially from mild infection, are suspected to not last as long as antibodies from a vaccine. This is because vaccines are specifically designed to get the best immune response possible, whereas the actual virus is doing everything it can during infection to avoid an immune response.

Additionally, your test might come with a number of antibodies you have made, normally expressed as AU/ml (antibody units per ml of blood). However, we don’t yet know what amount of antibodies is needed to create protection, so it hard to interpret this number.

Of course, it’s up to you as an individual to decide whether to take a COVID-19 antibody tests and they do have their uses. Here is our advice on how to interpret your result;

  • Discuss the result with your haematology team

They are used to dealing with patients with problems in their immune system and also know you personally (such as your specific blood cancer type, what treatment you have had, how good or bad your immune system is working at the present time). Therefore, they are best placed to advise, especially if you need medical advice around returning to work.

  • Weigh up the risks and benefits before you change your behaviour

If you have a negative result, you don’t necessarily need to lock yourself away (unless you have been advised this is necessary). As cases remain fairly low at the time of writing, you may feel that the risk is low enough that you are happy to start going out and about, even if you may not be fully protected. We would advise you continue to take extra care, such as wearing masks, ensuring you only go to well ventilated paces or stay outdoors and keeping the number of people you meet with to a minimum where possible.

If you have a positive result, do not stop following the rules and assume you are immune, for the reasons earlier in this article. It is important we all continue to take care

  • Get friends and family vaccinated

Regardless of your response, having others around you who are vaccinated is very important. This stops them from passing on COVID-19 to you, as well as stopping them from getting ill. You can now request that those you live with have their vaccination, under advice from the Joint Committee on Vaccinations and Immunisations (JCVI), even if your household aren’t yet eligible due to their age, so do speak to your GP about this.

For further information and advice, you can contact our advocacy team by:

    Blog post published on: 7th May 2021

    Blog post last updated on: 18th June 2021

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