What is the difference between antibodies to coronavirus and which test to take

We have been living in a pandemic for over a year.During this time, we literally merged with masks, got used to treating our hands with antiseptics, practically stopped shaking hands and learned a lot of new words. Today it is difficult to find a person who would not be aware of what COVID-19 is, oxygen saturation, mechanical ventilation and antibodies. But if everyone is afraid of the first three terms, then everyone wants to get the last one. Therefore, antibody tests have recently become extremely popular. Almost all laboratories and private medical companies began to offer them. But which test should you choose?

There are several types of coronavirus antibody test, and it is easy to get confused about them.

I was prompted to write this article by my personalhistory. I have already mentioned that I was vaccinated with two components of the Sputnik V vaccine. Therefore, it was interesting for me to see how the content of antibodies in my body will change. In total, I have planned to take 4 tests, of which 3 have already been passed by now. You can read about the results of the first two at this link. Both of them - which is logical - turned out to be positive and showed an increase in the titer of antibodies. However, the third test for some reason turned out to be negative! Let's figure out how this could happen.

My test came back negative, although I recently got both coronavirus shots.

How antibody tests differ

Most laboratories that do tests for antibodies to coronavirus offer several types of tests:

• IgG antibodies to spike (S) protein;
• IgG antibodies to nucleocapsid (N) protein;
• IgM antibodies;
• Antibodies IgM and IgG in total.

Immunoglobulin G, or, IgG - these are the same antibodies to coronavirus that are produced after a previous illness or vaccination.

Unlike immunoglobulins M (IgM), which indicates the presence of a virus in the body, they indicate the content of proteins in the body that can withstand COVID-19.

The tests themselves, in turn, are divided into several subspecies:

• Qualitative - the very fact of the presence of antibodies is determined, and the result is presented in the form of "positive" or "negative";
• Semi-quantitative - antibody contentis determined by calculating the positivity coefficient, that is, the optical density of the sample to the threshold value (this is not the concentration of antibodies, so the figure is likely to be low);
• Quantitative - it is the concentration of antibodies that is determined, which is presented in the form of relative units per milliliter of blood (the numbers are the highest).

But if everything is in principle with immunoglobulin Munderstandably - these are coronavirus antibodies indicating that the disease is ongoing at the moment - then many will not be able to distinguish IgG (S) from IgG (N). While both are antibodies that the body makes to fight off the coronavirus, they are not the same thing.

Spike protein or nucleocapsid antibodies

IgG antibodies to spike (S) protein produced in the body after the administration of the vaccine.This is a very effective type of antibody, and it is enough to protect most patients from contracting the new coronavirus infection. Scientists deliberately made the vaccine easier by removing IgG (N) from there so that vaccination does not hit the body too hard.

IgG (S) and IgG (N) antibodies are produced inthe body after a previous illness. At least they should. That is, IgG to the nucleocapsid (N) protein cannot appear in the body only after vaccination. Their content allows you to determine exactly where the antibodies came from in the patient's body. However, IgG (N), firstly, have a tendency to depletion, and, secondly, they may not be produced even as a result of a previous illness.

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Which antibody test to choose

Different tests need to be taken depending on whether you were sick or had the vaccine.

It turned out that my third test was done exactlyIgG to nucleocapsid (N) protein, not to spike (S). In most cases, these tests cost exactly the same and are named very similarly. Ordinary patients have no idea how they differ, because many laboratories operate with such specific terminology as spike and nucleocapsids.

No, of course, there is a mention here and therethe fact that the test for antibodies to the S-protein is done after vaccination, however, I did not find a single laboratory that would write that IgG to the nucleocapsid (N) protein appear after a previous illness. By the way, it was with this claim that I turned to Invitro, where they explained to me the difference in the tests, but they refused to compensate for the money spent on the wrong test, because I chose it myself.

Invitro, for example, does not write that another antibody test is needed after vaccination.

And so, let's once again and thesis:

• There is no better antibody test because each is highly specific and appropriate for a particular situation;
• IgG test to the spike protein it is recommended to do after vaccination;
• A test for IgG to nucleocapsid protein is recommended after COVID-19, but within 3-6 months (then antibodies disappear);
• Antibody tests may not show their presence at allbecause each organism perceives a virus or vaccine differently;
• Quantitative test for antibodies to coronavirus - the most expensive, therefore, if you are not interested in a figure, you can just make a high-quality one, which will determine the very fact of the presence of antibodies.

Ivan Kuznetsov, specially for Hi-News.ru