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With coronavirus cases on the rise due to the rapid spread of the new Omicron variant, one of the most frequently asked questions for those who have never had the disease is if they did indeed have Covid at some point, perhaps asymptomatically, and what needs to be done to find out.

There are different types of tests to verify if a person has contracted coronavirus, such as the hisopado nasofaríngeo (RT-PCR test), the saliva sample (PCR test) or the rapid antigen test. But those who want to find out if at any time they had the disease, they must undergo a serological test that allows to detect the antibodies generated by the organism against the virus. In other words, this type of analysis It determines if the person was infected, but it is not useful to know if the patient is having the disease at the time of the test.

To get a serological test, you have to undergo a blood draw, followed by analysis of the sample in a laboratory.
To get a serological test, you have to undergo a blood draw, followed by analysis of the sample in a laboratory.

There are two ways to do a serological test. The first is by drawing blood, followed by analysis of the sample in a laboratory, which yields effective indicators to quantify the immune response. The result can take between 24 and 36 hours. Those that measure igG+igM antibodies cost between 2,200 and 4,100 pesos. But there are laboratories that offer only the search for igG antibodies. In that case, the value of the analysis, on average, is 1,600 pesos.

Through the detection of igG and igM immunoglobulins in the blood can find out if a person was exposed to the coronavirus. There are five types of immunoglobulins: igA, igM, igG, igE (with various subtypes), igE (related to allergies), and igD. They are proteins that recognize, capture and block viruses so that the cells of the immune system (lymphocytes) can recognize them and eliminate them from the body.

The coronavirus testing center of La Rural de Palermo, in the city of Buenos Aires
The coronavirus testing center of La Rural de Palermo, in the city of Buenos AiresHernán Zenteno – THE NATION

According to information from experts, IgMs appear after four days as the body’s first defensive reaction against the virus, so their appearance in the blood serological test would indicate that it is very likely that the infection is in its early stages.

But the igG immunoglobulins, on the other hand, appear between 10 and 15 days after the infection, so their presence in the serological analysis could mean that the disease has already been experienced by that person. However, infectologists point out that, in the case of the coronavirus, both antibodies advance almost at the same time. IgM antibodies are the first to drop, while IgG remain high for a longer time.

Finger prick and result in 20 minutes: this is how the quick tests are
Finger prick and result in 20 minutes: this is how the quick tests areTomas Cuesta – THE NATION

The second option to find out if the coronavirus disease was diagnosed at any time is the quick tests using a blood sample taken from the fingertip, available in pharmacies at 2000 pesos. This type of exam give an answer in 15 minutes, although the test only shows whether or not the patient has antibodies, and does not provide more information than that, that is, it is not possible to quantify that result. They are very similar to a pregnancy test and they are insensitive.


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