Lydia ha
02/12/2021 6:01 AM
Clarín.com
Society
Updated 02/12/2021 6:01 AM
Given the advance of the coronavirus in the country, more and more people carry out antibody tests to detect the immune response against the pathogen.
The audience integrate those who have already had Covid and want to
know what level of immunity they have, and
health personnel
who wants to
know the effectiveness of
Sputnik V
.
“The demand for serological tests is currently
very important
, both in the AMBA and in the interior of the country.
There are, on the one hand, people who have had the infection or suspect that they have had and want to know if they have developed any type of antibodies and on the other hand, more recently,
health personnel who have been vaccinated and who want to know the immunity generated by the vaccine
.
In both cases, what they want to know is adaptive immunity, the humoral immune response that the organism has generated to the infection by the virus or to the vaccine, ”says
Andrés Albrecht
, vice president of the Argentine Chamber of Biochemical Analysis Laboratories (CALAB).
“At the end of December we had the first vaccinated.
Already today there are professionals who have traveled 42 days from the first dose, 21 days from the second dose and want to know
the protection status
.
This generates a new demand and consequently, new tests that are special to measure the immunity generated by the vaccine ”, explains the expert.
The tests available on the market to measure the immunity generated by the virus are not applicable to measure the immunity by the vaccine.
“The
new tests are serological but specific,
since what they determine are antibodies produced by the organism against the receptor-binding domain that the virus has on the human cell.
These tests are quantitative, that is, they measure the amount of antibodies that exist in the blood to be able to respond to the entry of a virus.
The amount of antibodies depends on the body's immune response to the vaccine, not all of us respond in the same way ”, explains Albrecht.
In
common cases
, the demand is spontaneous.
It is the same patient who wants to know their situation and turns to the doctor or goes directly to the laboratory.
Serological tests determine the
presence of IgM and IgG antibodies in the blood
produced by the body's defense system in response to Covid-19 infection and show whether or not a person was in contact with the virus.
A blood sample is tested for Covid-19 antibodies.
Photo: AFP
“Antibodies of an IgM nature appear
4 or 5 days after the onset of symptoms
, they can last three weeks and are very little useful for the diagnosis of the disease.
A positive IgM within 5 or 7 days of the onset of symptoms indicates infection, but it is very rare to find this circumstance, therefore IgM is not used for diagnosis.
While
IgG also
begins to appear on the fifth day of the onset of symptoms but they are 100% detectable from day 14 post symptoms ", explains Alfredo Martínez, coordinator of the Department of Clinical Analysis and Head of the Clinical Virology laboratory at CEMIC.
"These antibodies
indicate that he was in contact with the virus
and that once the symptoms disappeared the patient resolved the infection. These IgG antibodies are of different types but it is inferred that they would be protective, also called
neutralizing,
because they would prevent the individual from being reinfected ”, Adds Martínez,
“The detection of antibodies is a study that is carried out in blood, which is obtained by
venipuncture
(extraction of blood from a vein) and the most used methods are
chemiluminescent immunoassays
.
Chemiluminescence is a methodology that allows for
greater sensitivity and specificity
than other methodologies, as well as allowing them to be used in automated platforms (automatic equipment) ”, says the doctor.
An electron microscope image showing SARS-CoV-2 in yellow when it sprouts from the surface of cells grown in a laboratory.
PHOTO: EFE
And he adds, “the
levels of antibodies in individuals is variable
, for example, it has been observed that in patients older than 50 years the titres (amount of antibodies) are higher than in those under the age of 50, but it has also been seen that
not all infected develop antibody titers
.
This is still under study ”.
The objective of the serological tests is not to detect the SARS-CoV-2 virus (which causes Covid-19) and to identify whether or not the person has the coronavirus, but to check if they have been in contact with it and the body's immune response against it. virus in the form of antibodies.
As Martínez explains, “antibody tests are not used for diagnosis, they are requested to know if the infected patient has
adequate levels of protective antibodies
.
They are currently requesting it for the study of convalescent plasma to know the levels of neutralizing Ab (IgG-IgM SARS CoV2) that they possess in order to use convalescent plasma as a therapy in infected patients ”.
To know
if the values given by the test are high or low
, when the indicator obtained is close to the reference number, it is low;
For example, if the reference value is 50Au / mL and a value of 75Au / mL is obtained, this value is low.
But if the value is 450Au / mL, it is high.
The reference value
is defined by each laboratory
and depends on the methodology used.
If Abbott technology, one of the most widely used, is used, the reference value is 50Au / mL.
So if you have antibodies greater than 50 Au / mL, you have protective antibodies and have immunity against Covid-19.
According to the vice president of CALAB, serological tests also help to measure the
immunity that a population develops
.
They provide a more complete picture of how this population has been infected with SARS-CoV-2 and allow the detection of unknown cases that were not identified through systematic or active surveillance.
These tests are performed in a particular way in private clinics and laboratories, without a prescription.
And they do not have prepaid coverage or social work.
“In CABA, the tests cost between
2,500 and 3,000 pesos
when the dosages are carried out jointly and between 1,200 and 1,700 pesos, in the case of doing only one.
In the different regions of the country, the price varies according to the volume and the infrastructure, ”says
Matías Viniegra
, from the Viniegra Zanusso Laboratory.
It is not yet certain whether infected people, who subsequently recover and develop antibodies, are fully or partially protected against future SARS-CoV-2 infections or how long this immunity can last.
According to Martínez, “
the fact of having immunity does not imply total immunity
because we do not know how long these antibodies last.
This is also the reason why it is said that vaccination should be every year.
IgG antibodies create an environment of immunity that would prevent re-infection and decrease fatality.
But we are still learning ”.
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