Blood test for antibodies to the Covid-19 coronavirus in Moscow

This test evaluates the level of IgG only to the nucleocapsid protein of the new type of coronavirus SARS-Cov2, which caused the COVID 19 pandemic. It allows you to judge the state of immunity after an infection. It is not used to assess post-vaccination immunity.

The SARS-CoV-2 coronavirus consists of many proteins, the most immunogenic (causing an active immune response in the body) are the nucleocapsid protein (N) and Spike protein (S). IgG antibodies in the body in response to the introduction of coronavirus are produced at 3-4 weeks of illness to each of these proteins and persist for a long time (on average up to 10 weeks, according to preliminary data). The course of COVID 19 may be asymptomatic, in a mild form, or in a severe form with the development of pneumonia and respiratory failure, as well as other complications. Suspicious signs of COVID include a dry cough, loss of smell and taste, muscle pain, high fever, shortness of breath, and difficulty breathing.

Antibodies are produced both during obvious illness and during asymptomatic infection. The timing of detection of antibodies to coronavirus in the blood varies from person to person and depends on the activity of the immune system. In some of the sick people, IgG antibodies can be detected already in the 3rd week of the disease; in most cases, a sufficient level of antibodies in the blood is detected in the 5th week from the onset of signs of the disease. The presence of antibodies to the N-protein of the virus partially protects against recurrent disease upon contact with the Sars-Cov2 virus and indicates the presence of immunity after infection.

What does the analysis determine, what antibodies to COVID19 are tested for?

A blood test for antibodies reveals 2 types of immunoglobulins - proteins that the body produces in response to infection:

IgM antibodies are the first to appear in the blood of an infected person, from the moment of infection, as a reaction to the virus, and help fight the infection. Their identification means that the person is currently infected. In the first days, the concentration is low, so it may not be detected in a blood test. By the fifth day, the content increases, determined during testing.
IgG antibodies are produced later, after the tenth day of the disease. The maximum concentration is determined by the fourteenth day, then decreases. These are memory immunoglobulins; with their help, the body remembers the encounter with the virus. The presence of G antibodies means that a person has already encountered a coronavirus infection and has developed immunity.

Are there antibody tests that do not show post-vaccination immunity?

Yes. This is, for example, a test for “Antibodies to the nucleocapsid protein (N) of coronavirus IgG (performed by chemiluminescent immunoassay of serum and plasma, Abbot).

This test is not used to assess immune status after vaccination. The fact is that antibodies to the nucleocapsid protein (N) of the SARS-CoV-2 virus are produced only after an illness. Vaccination does not stimulate the production of these antibodies, so this test is useless for assessing post-vaccination immunity.

This test is prescribed:

to assess the patient’s expected immune status after suffering or in the late phase (recovery) of COVID-19 disease;
to assess the patient’s immune status, as an auxiliary method for diagnosing coronavirus infection, together with the results of other laboratory tests and clinical data about the patient.

What the results say

negative < 1.4 - negative (antibodies not detected);

positive > 1.4 – positive (antibodies detected).

What does antibody testing do?

There are two types of blood tests for COVID-19:

Qualitative. Express testing only detects the presence of antibodies in the blood.
Quantitative. Laboratory diagnostics ELISA (enzyme-linked immunosorbent assay) also determines the content (titer) of antibodies in the blood plasma.

Quantitative analysis is more informative; based on the concentration and ratio of immunoglobulins, it allows one to determine the stage of the disease - whether it is just developing or declining.

Additionally, it is recommended to undergo PCR testing to determine the virus itself. The study detects Covid-19 DNA in human biological material (oropharyngeal swabs) from the first day of infection.

Antibody test: why is it needed and how to do it correctly?

What kind of “beast” is this – antibodies?

“RG-Week” gives a comprehensive answer thanks to an interview with the head of the Scientific Center for Molecular Genetic Research DNAOM Andrey Isaev.

Why are antibody tests taken?

Tests are performed for the presence of antibodies (immunoglobulins) IgA, IgM and IgG.

- IgA antibodies are the first to be produced by our immune system in response to a virus invasion - if the test for them is positive, it means that the person is in the acute phase of the disease (even if he has no symptoms).

- IgM antibodies begin to be produced later, somewhere on the 3-4th day after the onset of symptoms - this type of antibody is also a marker of primary infection. Typically, testing for IgM antibodies is used as an auxiliary test to clarify the phase of the infectious process.

- IgG antibodies begin to be produced approximately 10-14 days after the onset of symptoms. Their appearance indicates that a person has developed long-term immunity. That is, we are talking either about the late phase of the disease, when the patient is already recovering, or about the fact that the person had COVID-19 earlier.

What test can be done before vaccination?

Currently, IgG antibody tests are most often performed by people about to get vaccinated to ensure they have not previously had COVID-19 asymptomatically or have naturally acquired immunity. If the test shows a positive IgG antibody titer, vaccination can be postponed.

What if a person wants to check the level of antibodies after vaccination? Now many people compare their performance.

You need to understand that the tests used in laboratories are different and the scales they use are also different. Therefore, if you try to compare results (although there is not much point in this), then you must at least be sure that you tested with the same test.

What is the "positivity rate"?

Semi-quantitative tests are used in most cases to determine antibody levels after vaccination. They do not show the exact amount of antibodies formed. But with their help, you can assess the intensity of the immune response - by the brightness of the sample, if the test is carried out using the enzyme-linked immunosorbent assay (ELISA).

Tests from different manufacturers have different scales. In most cases, state laboratories use Vector-best test systems, and their cut-off level is 1. That is, if the indicator is lower, there are no antibodies. From 1 to 1.1 is the so-called gray zone. If the result is higher than 1.1, it means that we have a strong positive reaction of the immune system.

The “positivity rate” shows how many times the level of antibodies in the sample exceeds the threshold level for their recognition. So, for example, the indicator of 15, which the president recently spoke about, is a good result. The majority of those vaccinated with Sputnik V or CoviVac have approximately the same or even higher rate of positive immune response.

At the same time, I would like to note once again that other test manufacturers may have a different scale and, accordingly, different indicators. At the same time, when you receive the test result in the laboratory, you can always see the reference values on the form and compare the result with them.

What test can be used to check post-vaccination immunity?

This test is called “Quantitative determination of antibodies to the RBD domain of the S1 protein of the coronavirus (IgG antibodies)” (performed by chemiluminescent immunoassay of serum and plasma, Abbot).

This is a quantitative test for IgG antibodies. It will help assess the immune response both in case of infection (or previous COVID-19) and to monitor post-vaccination immunity.

When to do it:

- for a current or past infection no earlier than three weeks after the onset of symptoms or a positive PCR test result;

— to assess post-vaccination immunity three weeks after the second dose of the vaccine.

What the results say:

<50.0 AU/mL negative: antibodies to the pathogen are absent or at a very low level. This may be a period of early infection or the patient may have impaired immune system function.
≥ 50.0 AU/mL positive: there is an immune response to the infection or a post-vaccination response has formed.

Are repeat studies needed?

Over time, the intensity of immunity, both in the case of a previous illness and after vaccination, decreases. According to infectious disease specialists, the higher the level of antibodies, the lower the risk of re-infection, as well as the likelihood of severe course and complications of COVID-19.

At the same time, it is recommended to do a repeat test to assess how the antibody level is falling no more than once every six months.

Are there antibody tests that do not show post-vaccination immunity?

Yes. This is, for example, a test for “Antibodies to the nucleocapsid protein (N) of coronavirus IgG (performed by chemiluminescent immunoassay of serum and plasma, Abbot).

This test is prescribed:

to assess the patient’s expected immune status after suffering or in the late phase (recovery) of COVID-19 disease;
to assess the patient’s immune status, as an auxiliary method for diagnosing coronavirus infection, together with the results of other laboratory tests and clinical data about the patient.

What the results say

negative < 1.4 - negative (antibodies not detected);
positive > 1.4 – positive (antibodies detected).

Why do you need to take a PCR test for COVID-19?

This test is taken to check whether a person is sick or possibly a carrier of the virus (even if he does not have any symptoms of illness), whether he is currently excreting the virus from the upper respiratory tract, that is, is a source of infection for others.

This is the only test for tourists that has already become standard: upon entry, almost all countries require you to present a certificate of the test taken before departure. After returning from the trip, you will have to take the test twice more and upload the result to the government services portal.

In addition, you can take a PCR test to make sure that you are healthy, that is, to exclude an asymptomatic course of the disease. This may be necessary if, for example, you are going to meet elderly relatives and you do not want to risk their health. In addition, with the help of such testing you can check whether you have become infected with coronavirus if you know for sure that you have been in contact with someone who is sick.

How to take tests correctly?

For the PCR test: a swab of biomaterial is taken from the nasopharyngeal mucosa. The test is taken on an empty stomach or three hours (or later) after eating. Three hours before taking a smear, you should not brush your teeth, rinse your mouth, drink, chew gum, or use antiseptic tablets, rinses or sprays.

For an antibody test: blood is taken from a vein. You need to donate blood on an empty stomach in the morning or afternoon, at least four hours after your last meal.

What does the analysis show, what does decoding the results mean?

For IgM antibodies. A positive answer means the person is infected in the acute stage. Negative - absence of Covid-19 or late stage when antibodies are no longer produced. Confirmed by PCR test.
For IgG antibodies. A positive answer is an infection in a late stage or an already suffered disease with the development of immunity. Negative - there was no infection or the disease was in an early stage. Confirmed by PCR test.

Only a doctor knows how to correctly decipher test results. You cannot draw conclusions on your own. Only a specialist can compare the received data and figures, on the basis of which a conclusion can be made about what result is normal. In case of doubtful tests for the presence or absence of antibodies, repeated testing is prescribed; additional PCR research is required.

What test can be done before vaccination?

What if a person wants to check the level of antibodies after vaccination? Now many people compare their performance.

Interpretation of the IgA test

Unlike the IgM/IgG analysis, the IgA test is carried out using the ELISA method. In addition to the qualitative detection of antibodies, ELISA also allows you to assess their level. In the transcript you will see conditional dimensionless coefficients, the value of which indicates a particular infection status. Consider these indicators:

Positive result – more than 1.1. Indicates the presence of an infectious process at the time of testing. If the patient does not have any manifestations of the disease, then this is most likely asymptomatic.
The borderline result is from 0.8 to 1.1. Speaks of the initial stage of infection. It is possible that immunoglobulin A has not yet been produced in sufficient quantities. In such cases, it is recommended to conduct a PCR analysis (to determine the RNA of viral particles in the body). It also wouldn’t hurt to re-test for antibodies after 2 weeks.
Negative result – less than 0.8. Such values indicate the absence of infection or its initial stage. PCR testing will help confirm the diagnosis.

Antibody research. Photo: standret / freepik.com

Types of antibodies

Since the onset of the COVID-19 pandemic, many have heard about immunoglobulins G (IgG) and M (IgM), but there are other types of antibodies. There are 5 types of immunoglobulins:

IgM - are formed in the first days after infection. These are acute phase antibodies². They are weaker than immunoglobulins G and break down more quickly. The presence of IgM indicates a recent illness.
IgG are part of the secondary immune response. These are antibodies that are produced after infection. They are needed in case the microbe suddenly appears again.
IgA is the main class of antibodies in mucous tissues. This is one of the elements of local immunity - protective reactions on the mucous membranes of the nasal cavity, mouth and throat (if we are talking about respiratory pathogens such as SARS-CoV-2)³.
IgE is responsible for protecting the body from parasites. They are also involved in allergic reactions.
IgD is the least studied class of immunoglobulins. It has been established that IgD is a membrane receptor. It is possible that these antibodies bind to certain blood proteins, causing an autoimmune disease to develop.

Figure 2. Simplified diagram of the immune response.
Image: website of the Club of Russian-speaking Scientists of the State of Massachusetts Today, enzyme-linked immunosorbent assays or immunochromatographic assays (ELISA and ICA) are most often used to determine antibodies against the new coronavirus.

The ELISA method is considered more accurate, since it is not only a qualitative, but also a quantitative analysis (shows the amount of antibodies per unit volume of blood). To do this, a person needs to donate blood at a medical facility or diagnostic laboratory.

ICA testing is an analysis using test strips. It shows only the presence or absence of immunoglobulins M and G.

The requirements for blood sampling for the ELISA and ICA methods are standard (as for other blood tests):

It is advisable to donate blood on an empty stomach;
before the analysis it is not recommended to drink coffee, juices, tea and alcohol;
It is also advisable to exclude water an hour before the analysis;
Smokers are not recommended to smoke, at least 1-2 hours before testing.

Why get vaccinated if you have antibodies?

Yasny Ilya Evgenievich, Ph.D., head of scientific examination of the pharmaceutical investment fund "Inbio Ventures":

“Antibodies are a simple attempt to answer a very complex question: Will your immune system protect you from getting infected again? Antibodies correlate with this, but are far from 100%. According to international recommendations, and this is the WHO, agencies of different countries - the USA, Great Britain, the European Union - antibodies are not a reason not to get vaccinated. There are cases where people got sick with high antibodies and even ended up in the hospital, but they are quite rare, and at the same time, there was a tendency for reinfection to be more likely with a low titer of antibodies after the first illness. Cases of recurrent disease will certainly increase. Because the virus evolves, more and more new variants appear that learn to infect people who have recovered from the disease. Many studies have come out that show that vaccination in those who have been ill very well increases the likelihood of protection against recurrent disease. That is, those who have recovered from the disease must be vaccinated! International recommendations are not talking about six months, but that you can get vaccinated immediately after the symptoms of the disease disappear. For most people, this occurs within a month of infection. As soon as a person feels healthy, he can go and get vaccinated. If you have been ill and have not been vaccinated before, I would recommend taking two components of the Sputnik V vaccine. It will not be worse".

Contraindications

There are no absolute contraindications to testing.

We do not take analysis:

if a person has signs of an infectious disease: fever, cough, difficulty breathing, shortness of breath, muscle pain, malaise;
in persons who have been in contact with a patient with COVID-19;
if a person has returned from a country with an unfavorable epidemiological situation;
for those in quarantine as prescribed by a sanitary doctor or Rospotrebnadzor;
in people with positive test results.

In such cases, call the clinic at your place of residence, the coronavirus hotline 8-800-2000-112 or Rospotrebnadzor 8-800-555-49-43.

BAU/ml - new interpretation of the test for antibodies to coronavirus

The World Health Organization has approved a new international standard for the determination of immunoglobulins for coronavirus, with the unit of measurement BAU (translated as “binding antibody coefficient”).

Interpretation of quantitative analysis for antibodies to coronavirus

Laboratory diagnostics of the level of immunity protection against coronavirus is carried out by studying immunoglobulins to the S protein of the virus. To facilitate the interpretation of the study results, it was proposed to use a universal measurement system.

Conversion table for antibody test results from different manufacturers in BAU/ml

Manufacturer	Conversion factor to BAU/ml
Abbott ARCHITECT	0,142
Roche	1

Interpretation of the IgG test

As in the case of IgA, the ELISA method is used for the qualitative and quantitative determination of class G immunoglobulins. The numbers are the same as for IgA, but the interpretation of the results is different:

A positive result is more than 1.1. This is the norm, which indicates the presence of immunoglobulins G against the new coronavirus. Most likely, the patient has already been ill with coronavirus disease for several months and humoral immunity has had time to form. In this case, other immunoglobulins (IgA and IgM) should be absent. Their presence indicates the stage of recovery.
The borderline result is 0.8-1.1. In this case, you need to re-test after 14 days. If testing was initially carried out at the initial stage of illness or recovery (up to 5 weeks), then repeated testing will show an increase in antibody titer.
A negative result is less than 0.8. This is the absence of IgG in the blood. Such a patient either did not have coronavirus disease or was tested in the acute phase of the disease, when IgG had not yet been developed.

Vaccination schedule

According to the NKPP, the course of prevention of the development of diphtheria, whooping cough and tetanus involves three-time vaccination.
Thus, the patient is vaccinated at 3, 4.5 and 6 months. At 1.5 years of age, primary revaccination is performed. When the child reaches 6 years of age, the immunization procedure is repeated. At 14 years of age, the third revaccination is performed. Afterwards, patients are vaccinated every 10 years from the date of the last vaccination. Important: since the timing of DTP administration coincides with the time of another important preventive measure - preventing the development of polio, both directions are combined.

DTP vaccination is not always carried out according to plan. Sometimes the immunization schedule changes. In some cases, the pediatrician develops an individual patient vaccination plan. There are many reasons why the prevention schedule may shift.

These include:

weakness of the body, passing through the acute stage of the disease during the vaccination period;
insufficient weight (the child was born premature) for immunization;
the patient’s absence from the territory of the Russian Federation for a period from 3 months to 1 year with the inability to be vaccinated with a domestically produced vaccine.

You should know: the DPT vaccine is only allowed up to 4 years of age. If the child did not have time to be vaccinated during this time period, the immunization procedure is carried out with ADS-toxoid (at 4–6 years old) or ADS-M-toxoid (for older patients). The latter provide protection to the body only from diphtheria and tetanus. There is no pertussis component in their composition. As for the prevention of polio, it is carried out separately.

References

Federal clinical guidelines. Laboratory diagnosis of rheumatic diseases. Moscow, 2014.
Rheumatology: national guide / ed. E.L. Nasonova, V.A. Nasonova. - M.: GEOTAR-Media, 2008. - 720 p.
Lapin, S.V., Totolyan, A.A. Immunological laboratory diagnosis of autoimmune diseases. - St. Petersburg: Man, 2010. - 272 p.
Lapin, S.V. Detection of antinuclear antibodies: international recommendations and personal experience, 2014.
Rheumatic diseases: nomenclature, classification, standards of diagnosis and treatment / ed. V.N.Kovalenko, N.M. Shuba. - M.: Katran group, 2002. - 214 p.