Ifa total at. Details about enzyme immunoassay blood test, what it is and its interpretation

Human immunodeficiency virus infection is a serious diagnosis. Errors in diagnosis can lead to disastrous consequences. An ELISA test for HIV is the most accessible research method, but it is not informative in all cases.

ELISA – enzyme-linked immunosorbent assay. The purpose of the ELISA method is to detect antibodies to the immunodeficiency virus in biological material. Using the method, you can track the presence in the liquid not of the viruses themselves, but only of the antibodies produced in response to their presence. Enzyme immunoassay is widely used in the diagnosis of STDs. It helps to identify sexually transmitted diseases.

There are several types of ELISA: direct version, indirect version, sandwich method. In any case, the technique is based on determining the presence of antibodies, which serve as an indicator of the penetration of a foreign agent. To identify these “tags,” the biological component is treated with enzymes.

Enzyme immunoassay determines antibodies with an accuracy of 96–98%, the error is insignificant. It is 2 – 4%.

ELISA – a method for diagnosing HIV

ELISA test for HIV is the first stage of diagnosis. The antigens of the immunodeficiency virus are proteins p24, p15, p17, p31 and glycoproteins gp 41, gp55, gp66, gp120, gp160.

To detect the viral protein, a portion of blood is taken from a vein. A sample sent for ELISA blood testing is treated with enzyme immunoassay reagents. Serum is isolated from the blood. If during the study they are found, it means that the virus is already present in the blood.

Blood is donated strictly on an empty stomach. It is not recommended to eat fatty foods or drink alcohol 2 days before the test. You should stop taking antiviral drugs for 14 days.

Advantages of the method:

• relatively low cost;
• high stability of reagents;
• high sensitivity;
• short duration;
• minimal influence of the human factor.

Modern ELISA test systems are produced according to international standards. This increases the accuracy of the method.

Enzyme immunoassay does not always give reliable results. After the virus enters the blood, the latent (hidden) stage of development begins. The period before viruses begin to multiply and antibodies have not yet formed is called the “seronegative window time.” There is no point in doing ELISA at this stage. If infection occurs, the result will be . How quickly the virus reveals itself depends on how many dangerous cells have entered the body. In case of unprotected sexual intercourse or transfusion of contaminated blood, this period will be minimal.

For high reliability of HIV ELISA, the test is carried out three times. Deadlines for taking ELISA for human immunodeficiency virus:

• 6 weeks after probable contact,
• in 3 months,
• six months later.

4th generation ELISA for HIV is a method that is most informative in the early stages of infection. It can be performed as early as 1 month after the suspected infection. The test is expensive compared to the 3rd generation analogue. Therefore, in public medical institutions it is used as an additional diagnostic method. Test 3 is carried out free of charge. If based on its results a definite answer cannot be given, the patient is referred to a 4th generation ELISA.

Important! Immediately after infection, a person becomes infectious. He is dangerous to others, even when he does not yet know about his diagnosis!

If ELISA reveals antibodies to HIV antigens, additional research is necessary. This includes . The reliability of this method is 80%. PCR tests blood, semen and vaginal discharge. The biological fluid is broken down in a medical reactor and then treated with enzymes. As a result, data is obtained on the concentration of HIV cells in the liquid medium. Due to the large error (20%), if the result is positive, immunoblotting is additionally performed.

The next stage of diagnosis is the Combo test (or immunoblotting). This is a highly sensitive test (98% confidence), which is carried out if ELISA results are ambiguous after 6 months.

Decoding ELISA results

Decryption time ranges from 24 to 48 hours. If it is necessary to obtain information urgently (surgery is required), decoding is carried out within 2 hours. Provincial medical centers do not always have the necessary reagents. The sample is taken at the place of application, then it is transferred to the regional center. Under such circumstances, the result can be found out in 1-2 weeks.

The result of an enzyme immunoassay can be either positive or negative; There are no other options.

Even if the result of the initial and repeated ELISA was positive, the patient cannot be recognized as HIV-infected. Subject to error. Reasons for a false positive result:

• chronic diseases;
• long-term infectious diseases;
• pregnancy.

Therefore, the result of the analysis should be clarified by additional studies.

If immunoblotting is HIV positive (reactive), the person is considered HIV-infected, which means he is healthy.

Over time, the virus cells adapt to the prescribed drugs. To control, the ELISA test is repeated periodically.

Sometimes immunoblotting shows a false negative result. It is extremely rare to have immunodeficiency virus for 6 months (or more). This is possible if a small amount of virus cells enters the blood. In 0.5% of the total number of cases, the infection can be diagnosed only after a year. In 99.5%, within six months after infection, ELISA will yield a reliable result.

Even with highly accurate studies, there is still a 2% chance of error. We should not forget about the human factor. To eliminate the possibility of error, the test can be performed in 2 different institutions.

How is an ELISA study carried out?

Reaction mechanism

The enzyme-linked immunosorbent assay is based on the immune reaction of an antigen with an antibody, and the attachment of an enzyme tag to antibodies allows the result of the antigen-antibody reaction to be taken into account by the appearance of enzymatic activity or by a change in its level. In a simplified form, the reaction mechanism can be represented as follows:

Calculation of results

Carrying out enzyme immunoassay

For serodiagnosis, 96-well polystyrene plates are used, on the walls of the cells of which the antigen is pre-adsorbed. The test serum is added to the cell of the tablet. In this case, antibodies homologous to the antigen are attached to it. Unattached antibodies are removed by washing. Next, antibodies against human immunoglobulins (antibodies) labeled with an enzyme are added to the cells. If detectable antibodies were present in the test serum, then at this stage they will act as antigens with which the labeled antibodies will react. The addition of a chromogenic substance (dye) after washing will allow us to take into account the reaction of the developing color in the cells. The intensity of the color is proportional to the amount of enzyme, and therefore the amount of antibodies. When measuring the optical density (OD) of a liquid in a cell and comparing it with a control sample, the concentration of antibodies is calculated in units of volume. The most often used is to calculate the results in units of optical density. It must be taken into account that Each test system has its own indicators for recording the results and indicators of normality and pathology that should be guided by when interpreting the results.

What infections can be detected by ELISA?

Mainly in modern venereology it is used for the diagnosis of syphilis (in combination with other reactions), HIV infection, viral hepatitis. It has limited value for the diagnosis of chlamydial infection, cytomegalovirus infection and other herpetic infections. The ELISA method is also used to determine antibodies in various infectious diseases , levels of hormones, autoantibodies and various markers of cancer.

How to interpret ELISA results

Studying the presence and level of antibodies of various classes in some cases helps determine the stages of the infectious process

Unfortunately, such an important advantage of ELISA as the quantitative determination of antibodies is not of great importance in practical work - i.e. does not allow an accurate diagnosis and does not affect the dosage and timing of medications.

What is the role of the ELISA method in the diagnosis of syphilis?

The ELISA method in the diagnosis of syphilis was first used in 1975. Currently, it is widely used for the serological diagnosis of syphilis in Russia and is used as a confirmatory test for syphilis. A study is usually carried out that identifies the so-called total antibodies to Treponema pallidum antigens (IgM and IgG) , although in some cases it is possible to determine only “early” antibodies of the M class. ELISA for syphilis becomes positive after 3 weeks from the moment of infection and remains positive for quite a long time even after treatment (sometimes for life). Therefore, as a test confirming the cure of syphilis, ELISA is not used. In most cases, only a qualitative determination of ELISA is carried out - i.e. only a positive or negative result, although quantitative determination is also possible.

ELISA (enzyme-linked immunosorbent assay, ELISA) entered the life of practical medicine somewhere in the 60s of the last century. Its initial task was histological research for scientific purposes, which boiled down to the search and identification of the antigenic structure of cells of a living organism.

The ELISA method is based on the interaction of specific (AT) and related antigens (AG) with the formation of an “antigen-antibody” complex, which is detected using an enzyme. This fact prompted scientists to think that the method can be used for diagnostic purposes to identify specific immunoglobulins of various classes involved in the immune response to a particular infection. And it was a breakthrough in clinical laboratory diagnostics!

The method began to be actively used only in the early 80s, and then mainly in specialized institutions. The first immunoenzyme analyzers were equipped with blood transfusion centers and stations, infectious diseases and venereology hospitals, since the formidable AIDS, born on the African continent, appeared on our horizon and immediately joined the “old” infections, required immediate diagnostic measures and the search for therapeutic drugs affecting him.

Scope of application of the ELISA method

The possibilities of enzyme immunoassay are truly extensive. Now it is difficult to imagine how one can do without such research, which is used in literally all branches of medicine. It seems, what can ELISA do in oncology? It turns out it can. And a lot. The ability of the analysis to find markers characteristic of certain types of malignant neoplasms underlies the early detection of a tumor, when it is not yet detected in any other way due to its small size.

Modern clinical laboratory diagnostics (CDL), in addition to tumor markers, has a significant arsenal of ELISA panels and uses them to diagnose various pathological conditions (infectious processes, hormonal disorders) and monitor pharmaceutical drugs in order to identify their effect on the patient’s body and, by the way, not only human. Currently, enzyme immunoassay is widely used in veterinary services, because “our little brothers” are also susceptible to many diseases, from which they sometimes suffer greatly.

Thus, ELISA, due to its sensitivity and specificity, can determine from a blood sample taken from a vein:

• Hormonal status (thyroid and adrenal hormones, sex hormones);
• The presence of viral and bacterial infections (HIV, B and C, chlamydia, syphilis, and, and, as well as many other diseases caused by pathogenic microorganisms);
• Traces of the vital activity of microorganisms that initiated the infectious process, which ended successfully and moved into the stage of forming an immune response to this pathogen. Such traces, that is, antibodies, in many cases remain circulating in the blood for life, thereby protecting a person from re-infection.

What is the essence of ELISA?

The enzyme immunoassay method allows one to determine not only the presence of the pathogen itself (qualitative analysis), but also its quantitative content in the patient’s blood serum.

The viral or bacterial dose significantly influences the course of the infectious process and its outcome, therefore quantitative analysis plays an important role in the diagnosis and treatment of diseases in various forms and stages.

However, knowing enzyme immunoassay studies as the ELISA method, we don’t even think about how it manages to cover such a wide range of microorganisms inhabiting our planet, many of which pose a direct threat to the health and life of humans and animals. But the fact is that ELISA has many options (non-competitive and competitive - direct and indirect), each of which solves its own problem and, thus, allows for a targeted search.

To identify immunoglobulins of one class or another, a traditional 96-well polystyrene panel (plate) is used, in the wells of which sorbed recombinant proteins are concentrated in the solid phase. Antibodies or antigens that get into the well with blood serum find a “familiar” object and form a complex with it (AG - AT), which, fixed by an enzyme conjugate, will appear as a change in the color of the well when reading the results.

Enzyme immunoassay is carried out using test systems of a certain specificity, manufactured in special laboratories and equipped with all the necessary reacting components. Research can be carried out using washing machines (“washers”) and reading spectrophotometers, which mostly involve manual labor. On full automatic machines, which free the laboratory assistant from monotonous instillation, washing and other routine tasks, of course, it is faster and more convenient to work, but not all laboratories can afford such luxury and continue to work the old fashioned way - on semi-automatic machines.

The interpretation of ELISA results is within the competence of the laboratory diagnostics physician, and the inherent property of almost all immunochemical reactions to give false-positive or false-negative answers must also be taken into account.

Video: modern enzyme immunoassay

ELISA results using the example of syphilis

Enzyme immunoassay is suitable for detecting all forms, and, in addition, is used in screening studies. To carry out the analysis, the patient's venous blood taken on an empty stomach is used. The work uses tablets with a certain specificity (AB classes A, M, G) or total antibodies.

Considering that antibodies in syphilis are produced in a specific sequence, ELISA can easily answer the question of when the infection occurred and at what stage the process is, and the interpretation of the results obtained can be presented in the following form:

• IgM indicates the duration of the infectious process (may appear during exacerbation of chronic inflammatory diseases);
• IgA states that the infection occurred more than a month ago;
• IgG indicates that the infection is in full swing or that treatment has been recently carried out, which is easily determined by taking an anamnesis.

When testing for syphilis, negative wells (and the negative control) will remain colorless, while positive wells (and the positive control) will show a bright yellow color due to the color change of the chromogen added during the test. However, the color intensity does not always coincide with the control, that is, it may be slightly paler or slightly yellowish. These are dubious results, which, as a rule, are subject to re-examination with mandatory consideration of the quantitative indicators obtained on the spectrophotometer, but in general, the color is directly proportional to the number of immune complexes (associated Ags and ATs).

The most exciting of the enzyme immunoassays is the HIV ELISA

Analysis on is perhaps more interesting than others to a wide range of the population, because it is not yet possible to say with confidence that many social problems have disappeared (prostitution, drug addiction, etc.). Unfortunately, HIV affects not only these layers of human society; you can become infected under various circumstances not related to sexual immorality or drug use. But if there is a need for an HIV test, you should not be afraid that everyone around you will know about your visit to such a laboratory. Now HIV-infected people are protected by law, and those who have doubts can turn to anonymous offices where they can solve the problem without fear of publicity and condemnation.

The enzyme immunoassay method used to diagnose HIV infection is one of the most important standard studies, which, however, requires special conditions, since the topic is very delicate.

It makes sense to carry out HIV ELISA after sexual contact, blood transfusion, other medical procedures that suggest infection, and at the end of the incubation period (“seronegative window”), but it should be borne in mind that this period of time is not constant. It can end in 14-30 days, or it can last up to six months, so the average value is considered to be an interval from 45 to 90 days. Blood is donated for HIV in the same way as for other infections - from a vein on an empty stomach. The results will be ready depending on the accumulation of material in the laboratory and its workload (from 2 to 10 days), although most often laboratories provide an answer on the same day or the next.

What can you expect from your HIV results?

ELISA for HIV infection detects antibodies to two types of the virus: HIV-1 (more common in Russia and other countries of Europe and Asia) and HIV-2 (more common in West Africa).

The task of the HIV ELISA is to search for class G antibodies, which are detected on all test systems, but at a later period, and class A and M antibodies, detected on new generation recombinant test kits, which make it possible to find antibodies at the earliest stages (incubation period - "seronegative window"). You can expect the following answers from the ELISA:

1. Primary positive result: the blood must be retested using a test system of the same type, but if possible of a different series and by another person (laboratory assistant);
2. Repeated (+) involves a new blood draw from the patient with its examination similar to the primary analysis;
3. Another positive result is subject to reference analysis, which uses highly specific test kits (2-3 pcs.);
4. A positive result in both (or three) systems is sent for immunoblotting (the same ELISA, but performed individually using test kits of particularly high specificity).

The conclusion about HIV infection is made only on the basis of immunoblotting. A conversation is conducted with the infected person in complete confidentiality. Disclosure of medical secrets in Russia, as well as in other countries, is subject to criminal punishment.

Tests for chlamydia and cytomegalovirus using the enzyme immunoassay method have also gained particular popularity, due to the fact that they make it possible to determine the time of infection, the stage of the disease and the effectiveness of treatment measures.

During implementation, one can also observe the appearance of antibodies of various classes. in different phases of the pathological condition caused by an infectious agent:

• IgM can be detected as early as seven days after infection;
• IgA indicates that the infection has been living in the body for more than a month;
• IgG confirms the diagnosis of chlamydia and helps monitor treatment and determine its effectiveness. It should be noted that class G antibodies remain and circulate in the body regardless of the duration of the disease, therefore, to correctly interpret the analysis, you need to take into account the reference values ​​(norms), which, by the way, are different for each CDL: taking into account the brand of the test system and the specificity of the reagents included in the set. The normal values ​​are entered in the form next to the ELISA result.

As for , it’s a little different here: class M antibodies appear after about a month to a month and a half, that is, the positive result (IgM+) becomes in the phase of primary infection or during reactivation of a latent infection and remains so from 4 months to six months.

The presence of class G antibodies is characteristic of the onset of a primary acute infection or reinfection. The analysis states that the virus is present, but does not provide information on what stage the infectious process is at. Meanwhile, determining the normal IgG titer also causes difficulties, since it entirely depends on the immune status of a particular person, which, however, is established by identifying class G immunoglobulins. Given this behavior of antibodies, when diagnosing CMV, there is a need to assess the ability of class G antibodies to interact with CMV, in order to later “neutralize” it (AT avidity). At the initial stage of the disease, IgG binds very poorly to viral antigens (low avidity) and only then begins to show activity, therefore, we can talk about an increase in the avidity of antibodies.

We can talk a lot about the advantages of enzyme immunoassay, because this method was able to solve many diagnostic problems using only venous blood. There is no need for long waits, worries and problems with collecting material for research. In addition, test systems for ELISA continue to be improved and the day is not far off when the test will give a 100% reliable result.

Video: educational film of Moscow State Medical University named after. Sechenov on the basics of ELISA

The enzyme immunoassay method is a modern method of laboratory testing of blood for the presence of antibodies to viruses and antigens to pathogens. This method can not only identify the etiology, but also determine the stage of the disease. The results of the analysis have a qualitative and quantitative indicator.

Why enzyme immunoassay is performed:

• blood examinations () for the presence of autoimmune diseases in it;
• examination of the patient for tumor markers;
• the ability to study the hormonal composition of the blood;
• search for antigens to infectious and venereal diseases;
• search for antibodies to viral infections.

The advantages of enzyme immunoassay are that it guarantees a high level of specificity of results and has high sensitivity (more than 90%) to infectious agents. ELISA is an accessible diagnostic method that is performed in every medical center. Also, using this method, you can determine not only the disease, but also monitor the process of its development, comparing the amount of protein produced in the blood at different periods of time.

The only drawback of ELISA, perhaps, is that it cannot be used to determine the causative agent of the infection, but can only identify the immune response to this pathogen.

Basic terms of enzyme immunoassay (ELISA)

First, let's understand some concepts to understand the principle of conducting laboratory research.

An immune complex is a complex of antibodies and antigens present in the blood that participate in the immune process.

Antigens are substances that are of organic origin and are formed as a result of a particular disease in the cells of the body. The cause of this may be an autoimmune disease or cancer. Also, antigens can be substances of various pathogens of infectious diseases.

Antibody avidity is an indicator of the strength of the bond between antigen and antibody, as well as the amount of antigen that has come into contact with antibodies (immunoglobulins).
This is a very important indicator, since it can be used to determine the date of infection of a person, which is very important when infected during pregnancy.
The avidity test is performed in a laboratory by treating the antibody-antigen complex with urea, which destroys the protein. In this case, compounds with low avidity are destroyed, while compounds with high avidity remain intact. Avidity test results are expressed as a percentage.

Antibodies (immunoglobulins) are a special protein that is produced by lymphocytes, that is, immune cells, when bacteria, viruses or fungi (an infectious pathogen) enter the human body.
There are five types of immunoglobulins: A, E, M, G, D. They differ from each other in weight, shape, participation in the infectious process, half-life, and time of formation from the moment of infection.
The largest molecular weight is immunoglobulin IgM (pentamer), it weighs 950,000 daltons, while the rest have a weight in the range of 150 - 200,000 daltons. Due to its size, IgM does not cross the placental barrier. In serum from the blood, the bulk is occupied by IgG immunoglobulins, their percentage is approximately 80%. And the smallest part in the serum is occupied by IgE antibodies - 0.003%. Immunoglobulins IgG, IgM, IgA are involved in the infectious process. While IgE is the result of allergic reactions. Proteins such as IgD take part in the formation of local immunity and are formed in the lymph nodes and tonsils.

There are several types of ELISA, including direct, indirect, competitive and blocking methods. Although in practice, laboratory technicians most often use a solid-phase heterogeneous immunoassay called ELISA (enzyme linked immunosorbent assay).

The principle of enzyme immunoassay is manifested in the reaction of an antibody and an antigen, in which an immune complex is formed - antigen-antibody. This reaction causes the enzyme activity of the labels on the surface of the antibodies to change.

To understand this, let's look at this process step by step.

First stage. At this stage, the laboratory technician conducting the study places the purified antigen of the infectious pathogen on the surface of the wells of the plate. Then, the patient's blood serum is added to the pathogen, which provokes a specific reaction between the antibody in the blood and the antigen. This resulting compound is involved in the next stage of the experiment.

Second stage. At the second stage of the study, the formation of immune complexes occurs, which are a reaction between the antigen obtained in the first stage and the conjugate, that is, immunoglobulin labeled with the peroxidase enzyme. In this case, a specific chromogen is added. The reaction produces a colored compound in the well. The intensity of the color depends on the amount of immunoglobulins contained in the patient’s blood.

Third stage. At the third stage, laboratory assistants are usually involved in assessing the results of the study. To do this, photometry is carried out using a spectrophotometer, the density of the biological material is compared with the density of the samples, and a mathematical calculation of the results is also carried out. The level of immunoglobulins in the blood depends on the density of the plate well.
In practice, 96-well plates are most often used.

When the optical density (abbreviated DI) of blood is measured, antibodies are counted in one unit of volume. Then the obtained result is compared with the control material.
It is important to remember that for each research method its own indicators are established, with the help of which the reference values ​​of the test are taken into account. These are indicators of pathologies and norms. Therefore, you need to remember this in each specific case. The results of one study cannot be interpreted into another. Also, it is impossible to compare the results of individual laboratories.

Diseases detected by ELISA diagnostics

Using enzyme immunoassay, it is possible to detect the presence of the following diseases in the body:

1) Infectious diseases

2) Indicators of the state of human immunity and markers of autoimmune diseases.
3) Oncological diseases (chronic gonadotropin, prostate-specific antigen, alveomucin, tumor necrosis factor, carcinoembryonic antigen and others).
4) Endocrine diseases.
5) Disorders of the reproductive system.

The list does not include all diseases that can be diagnosed using ELISA; the list goes on.

Research

Collection of material for research using enzyme immunoassay.

For ELISA studies, spinal substance, vitreous fluid, amniotic fluid, mucus isolated from the cervical canal or urethra, as well as smears can be taken from patients. But the most common sample for research is still the patient’s blood.

Enzyme immunoassay results are usually available within 24 hours. Delays should not occur, although with large accumulations of serum, laboratory assistants may simply not be able to do the analysis on time.

Research results

When assessing the results of studies conducted to identify any infections, the number of immunoglobulins found in the blood, as well as their type, is of particular importance. The presence of infection in the body or its absence depends on these indicators. Also, by comparing quantitative and qualitative indicators, the laboratory technician can determine the expected stage of development of the disease, as well as distinguish the acute form of the disease from the chronic form. The presence of an active virus in the human body is also assessed, which manifests itself in an aggravated chronic or acute form of the disease.
The approximate time after which Ig immunoglobulins appear in the blood.

The fact is that IgM are the fastest appearing antibodies. They are detected within 1 to 3 weeks after the process of infection of the body; this is a sign of the acute phase of infection with the human virus.

Also, such antibodies can be detected in the patient’s blood during an exacerbation of a chronic disease. The amount of IgM antibodies persists for about 3 months from the moment of their formation, then they gradually begin to disappear. Although there are exceptions. For example, some patients retain the amount of antibodies in their blood after final recovery. Thus, the circulation of immunoglobulins occurs several years after infection.

In such patients, it is necessary to check positive indicators for the presence of IgM antibodies, since there may be situations where the testing system makes an error and produces a false positive result. Such situations happen very often to pregnant women.

As for the appearance of IgA antibodies, they can form 2 or 4 weeks after the body has been exposed to infection. But antibodies can be detected only after a month. It is then that their number reaches the optimal number for identifying the number.

IgA antibodies are produced by cells of the lymph nodes, spleen, and mucous membranes. Such immunoglobulins are able to concentrate on the surfaces of the mucous membranes of organs, where they perform their protective function, participating in local human immunity.

The appearance of IgG antibodies can be traced by testing systems as early as 4 weeks of progression of the infectious process in the body. The titer of such immunoglobulins can gradually increase over 2 months. After recovery, a small titer of them remains in the body and supports the immune system. Diseases such as chlamydia, trichomoniasis and mycoplasmosis are characterized by low levels of IgG antibodies in the blood, which is explained by the lack of stable immunity to such infections.

Classes

Options for detecting immunoglobulins of different classes in human blood.

• Detection of IgM antibodies, which is carried out in isolation, indicates primary infection of a person.
• Detection of both IgM and IgG class antibodies in the blood serum also occurs during primary infection that occurred in the last 2-3 months. Or this combination may be a sign of an exacerbation of a chronic disease.
• Thus, such results during pregnancy do not always indicate primary infection.
• Detection of IgG antibodies in isolation may be a sign of immunity to this infection, although it may also indicate a chronic disease. In the presence of a chronic form of the disease, the number of antibodies and their dynamics play an important role. Such studies are carried out at intervals of approximately 2 weeks.
• When both IgA and IgM antibodies are present in the blood, this may indicate a primary infection. Detection of IgA in isolation is also a consequence of the primary infection of the body.

When IgA antibodies are detected together with IgG antibodies, this means activation of the chronic form of infection. Immunoglobulins appear in the blood 2 weeks after an exacerbation of the disease.
Antibody avidity is an indicator of the strength of the bond between antigen and antibody, as well as the amount of antigen that has come into contact with antibodies (immunoglobulins). This is an additional step in diagnosis using the ELISA method.

This is a very important indicator, since it can be used to determine the date of infection of a person, which is very important when infected during pregnancy. And also, you can assess all the risks of intrauterine infection of the child.

The avidity test is performed in a laboratory by treating the antibody-antigen complex with urea, which destroys the protein. In this case, compounds with low avidity are destroyed, while compounds with high avidity remain intact. Avidity test results are expressed as a percentage. High avidity of antibodies indicates a chronic form of the disease, or is a sign of stable immunity.

Features of the appearance of antibodies in the blood of infants

If maternal IgG is found in the blood of children under the age of one year or up to 1.5 years, this means that the antibodies entered the child’s body through the placenta during gestation. This sign cannot indicate infection of the baby, but is immunity to infection transmitted from the mother.

But, if immunoglobulins of the IgM class are found in a small organism, which, due to their weight, cannot penetrate through the placenta to the baby, then this is a sign of infection. Infection could occur after birth or during fetal development.

Quantitative enzyme immunoassay method.

The result of diagnosing diseases using ELISA is presented in certain units of measurement:

1. OD – optical density of a sample is the level of antibody concentration in one unit of volume. The higher this indicator, the more immunoglobulins are in the blood.
2. Some ELISA results imply the presence of such a unit as the positivity coefficient - CP. This is also a designation of the density of the sample.
3. Units of immunoglobulin concentration are expressed in nanograms, milliliters or ng/ml.
4. Blood serum titers are expressed as follows: 1:20, 1:40, 1:100, 1:200, 1:400, 1:800, 1:1200 and the like.
5. The titers at which the disease is diagnosed are different for different infections.
6. The research results contain the following symbols: “-”, “+”, “?” (+, ++, +++, ++++).
7. A qualitative assessment implies the presence of only one point out of two: positive or negative.

The correct interpretation of the results of this study depends on the qualifications of the doctor, since no one other than a specialist has the right to prescribe treatment.

Experts evaluate the amount of antibodies in the blood, their type and concentration.

Also, it is necessary to remember that it is impossible to compare the results of different research methods, or the results of tests obtained in different laboratories. Since any diagnostic method has its own indicators and units of measurement.

Comparison of results is only permissible within the same laboratory.

Video of the ELISA immunoassay method