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Antibody tests. What are they and what is their use?

Self-diagnostic antibodies tests against COVID-19 are now available for particular use. To understand what they are, we first need to know how they work and what they detect. Here we go!

What does a COVID-19 antibody test detect?

The covid antibodies test uses a blood sample to see if you have IgM or IgG antibodies for covid-19. Antibodies are protein molecules that are synthesised by our immune system when we have been exposed to pathogens to block the spread of infection, although they are not the only defense mechanism we have.

Ig indicates that they are immunoglobulins, a special type of protein, and the letters M or G indicate that they are two different antibodies: the M type appears at the beginning of the infection, while the G type appears after several days. In the case of COVID-19, 7-10 days after infection are estimated for the appearance of the first IgM, and 10-15 days for the appearance of the first IgG. IgM ceases to be detected before IgG.

How is a COVID-19 antibody test performed?

The package leaflet describes how to do it, and you should follow the instructions carefully. But basically, a blood sample is obtained by finger prick, as with the glycaemia tests we do at the pharmacy. The drop of blood is put into a cassette like a pregnancy test, but smaller, and can give one of these results:

How are the results of the COVID-19 antibody test interpreted?

This is where the problems begins:

The first interpretation is “the biological one”, so to speak. As they are antibodies, we are talking about an infection that has already begun, and above all, has already passed; depending on the Ig that appears, we can estimate whether it is a recent or an old infection.

The second interpretation is “the practical”: What do I do now: should I confine myself because there is still a risk of infection, or can I go outside? Is my health at risk, or is it all over and I can say that I am cured?

Interpreting the results is a task for qualified personnel, as the same results may indicate one or the other depending on your clinical picture or your history of exposure to the virus. There may even be some doubtful results that require PCR confirmation, especially in the first few days of infection.

What is a COVID-19 antibody test for?

Basically, an antibody test shows whether or not you have been exposed to the coronavirus and can give an idea of whether it was recent or distant in time, but without the clinical information it is difficult to make a more thorough interpretation of each case. These tests are very useful in the context of epidemiological studies to obtain population information, i.e. to know how exposed a social group was to COVID-19.  They also help to identify potential plasma donors for COVID-19 treatment.

What is an antibody test NOT for?

To consider yourself immune to COVID-19. There is evidence that it is possible to get COVID-19 again, and it is not known exactly how long these antibodies protect you.

To find out if you can infect others. This information is provided by PCR or antigen tests.

To stop applying protective measures, such as distance, masks and hands cleaning. Whatever the result of the test is, these measures must still be applied.

If you would like to know more about these tests, or if you would like help in assessing whether or not they are useful for you, you can talk to your pharmacist. Pharmacists are trained to understand how these tests work, answer your questions, and only if we see that the test might be right for you we will refer you to a doctor for a final assessment.

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