Serological tests have the role of detecting the body’s immune response following infection with the SARS-CoV-2 virus. In other words, it identifies, following the analysis of a blood sample, the antibodies that the body produces after coming into contact with the coronavirus, which can remain in the body for up to several months.
Following exposure of the organism to coronavirus, antibodies from IgM and IgG classes appear
To date, only three classes of antibodies are studied in the dynamics of the immune response, generally induced by viruses: antibodies of type A, M and G. For coronaviruses and especially for SARS-CoV-2, the role of IgA antibodies is little understood. IgM and IgG antibodies have been studied since the onset of the pandemic and with the development of laboratory tests.
- IgM type antibodies – Immunoglobulin M are produced by the immune system immediately after infection, being present in the first line of defense during viral infections.
- IgG antibodies – G immunoglobulins are extremely specific antibodies that are important for long-term immunity and immune memory.
In general, IgM antibodies appear first, but in the case of SARS-CoV-2 it has been observed that IgM and IgG antibodies can appear and persist almost simultaneously.
Anti-protein N (nucleocapside) and anti-protein S (spike) antibodies
In terms of role protein N (nucleocapsid), which encapsulates the viral RNA and protects it from the host cell environment and protein S (Spike), whose subunits make it possible to attach the virus to the cell, penetrate the virus into the cell and fuse it with the host cell, they are highly immunogenic.
Studies have shown that anti-N antibodies can be detected earlier, but they persist a little less than anti-S antibodies. On the other hand, among the anti-Spike antibodies, most antibodies are recruited with the role of neutralizing the infectivity of the virus, ie to block the binding domain to the host cell, a character that can give them the status of protective antibodies.
The tests detect anti-protein N (nucleocapsid) and S (spike) antibodies in the blood, because they play an important role in SARS-CoV-2 infection and cause a significant production of antibodies. ”The identification of anti-protein N (nucleocapsid) and / or anti-protein S (Spike) antibodies, of the IgG and / or IgM type, indicates an indication of a previous SARS-CoV-2 infection, without specifying, however, the distance from the time infectious or symptomatic route ”, explains Dr. Daniela Stratomir, primary physician in laboratory medicine at MedLife.
On the other hand, experts point out that the absence of IgG or IgM antibodies does not certainly rule out a possible previous SARS-CoV-2 infection. Anamnestic, clinical, epidemiological data and RNA detection by RT-PCR, are the elements that must be the basis of medical judgment.
What type of tests are recommended for antibodies after vaccination or infection?
If you do not know you have had COVID-19 infection, but you think you may have come in contact with the virus and been asymptomatic or if you have had symptoms that you have associated with other types of respiratory infections it is recommended that you do a anti-N (nucleocapside) IgG qualitative test, the result of which confirms or refutes the presence of antibodies, without specifying their concentration.
Instead, if you have previously been infected with SARS-CoV-2, whether you have a mild, moderate or severe form and want to know if your body has produced antibodies, in addition to qualitative test for the detection of anti-nucleocapsid IgG antibodies, the test for anti-Spike antibodies is also recommended, which quantitatively measures the concentration of IgG antibodies.
It is also used to monitor the immune response to vaccination test for anti-Spike IgG antibodies. The current vaccines available in Romania sensitize immune cells and induce the production of anti-S antibodies, which prevent the virus from entering and multiplying in the body. However, you should keep in mind that if you have not been in contact with the virus before vaccination, the antibody titer may only become significant after the second dose of vaccine.
“It is expected that after the first dose of vaccine, the immune response will not be very intense in people who have not been in contact with the SARS-CoV-2 virus. However, the booster comes to strengthen the memory of the antibody-producing cells, so that the immune response is long-lasting and strong enough to neutralize a future viral infection.“, Added Dr. Daniela Stratomir.
How is the test result interpreted for antibodies?
A negative result of IgM and IgG serological tests indicates either that the person tested did NOT come into contact with the SARS-CoV-2 virus or that the time from the time of encounter with the virus is still insufficient for the development of antibodies. If you suspect that you have been exposed to SARS-CoV-2 virus infection, it is recommended that you contact your family doctor or treating physician. In this case, RT-PCR testing, the safest test method for the diagnosis of COVID-19 infection, is required.
A positive IgM result may indicate a possible acute infection, given that IgM-type antibodies are produced by the immune system immediately after infection.
A positive IgG result most likely indicates previous contact with SARS-CoV-2 virus, either following infection or vaccination. This result suggests that the person was exposed to the virus until harvest, regardless of whether he or she had specific symptoms or was asymptomatic.
Doctors explain that there is still no agreement on the concentration (or titer) of neutralizing antibodies that provide protection against a new SARS-CoV-2 infection, which is why the results of serological tests are interpreted with caution, assuming: as the concentration of binding antibodies is higher than the range set by the manufacturer, it is believed that there is an increased neutralization antibody titer, especially in the case of anti-S antibodies.
At the same time, specialists point out that the values of antibody tests are not intercomparable from one manufacturer to another, so the results may differ depending on the laboratory.
MedLife makes both available to patients individual assays for antibody detection anti-S or anti-N, IgM and IgG type, as well as post-immunization packages for assessing immune status following vaccination or SARS-CoV-2 infection.
Take a test for the nearest anti-SARS-CoV-2 antibody harvesting center MedLife and find out the immune status of your body after infection or vaccination.
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The article is part of the campaign MedLife We are doing Romania well.
We have been with you for 26 years and we do not stop. Because today, more than ever, medicine means fighting through science and knowledge.
To meet our patients with a wide range of services and tests adapted to current needs, we have aligned ourselves with international standards and opened our own Real Time PCR laboratories to detect the SARS-CoV-2 virus. We have invested in the necessary infrastructure to assess whether the patient has gone through the disease and to test the post-infection or post-vaccination immune response.
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