Features of a blood test by ELISA and decoding

Enzyme-linked immunosorbent assay is used in various fields of medicine.

But in most cases, this method diagnoses a wide range of infectious diseases, such as human immunodeficiency virus, hepatitis, herpes and other infections of the genital organs.

An enzyme-linked immunosorbent assay is also used to identify tumor markers of various origins, determine hormones, and diagnose the reproductive function of the body. The material for an enzyme immunoassay is human blood.

Medical laboratories use several options for its implementation, which affects the shelf life of the results. But on average, the issuance of research results occurs in the period 1-10 days after blood donation.

With this type of blood test, antibodies of different types are established – these are immunoglobulins of class M, A, G (JgM, JgA, JgG). Their accumulation occurs at various time intervals.

Class M immunoglobulins begin to appear first (fifth day after the onset of the disease). Such immunoglobulins are retained in the body for five to six weeks, after which they begin to disappear from the bloodstream.

It is in this period of time that class M antibodies are detected.

Class G immunoglobulins appear second (after three to four weeks). They linger in the body for several months or years. During an enzyme-linked immunosorbent assay and decoding its result, an increase in class G antibodies can be detected. This indicates the presence of infection or reinfection.

Class A antibodies appear in the blood for two to four weeks. But only 20% of them are present in blood serum. The rest are part of the secret of the mucous membranes.

Class A immunoglobulins begin to disappear in a period of time from two weeks to two months. This process is evidence of the destruction of the infection in the body.

If after a person’s recovery, an enzyme-linked immunosorbent assay was performed and deciphering the result showed the presence of class A antibodies, this is evidence of a chronic infection.

With an enzyme-linked immunosorbent assay, the decryption of the results can take the following values:

  • JgM (-), JgG (-), JgA (-) – lack of immunity to infection;
  • JgM (-), JgG (), JgA (-) – the presence of post-vaccination or post-infection immunity;
  • JgM (), JgG (- /), JgA (- /) – the presence of acute infection;
  • JgM (), JgG (), JgA () – the presence of exacerbation of chronic infection;
  • JgM (-), JgG (/ -), JgA (/ -) – the presence of a chronic infection;
  • JgM (-) – recovery.

It should be remembered that with an enzyme-linked immunosorbent assay in the decoding () is a positive result, and (-) is a negative result.

In addition to clarifying the classes of antibodies during enzyme immunoassay in the decoding, their quantitative indicators are found. But their vast explanation can only be provided by the attending physician.

Blood serum is a clear liquid with a yellow tint. After blood coagulation, it is separated from the blood clot. It does not contain fibrin and uniform elements. Blood serum is used in an enzyme immunoassay.

An enzyme-linked immunosorbent assay is based on the interaction of an antigen with an antibody, one of which contains an enzyme in its structure.

In other words, the principle of an enzyme-linked immunosorbent assay can be explained as follows:

  • sets of antigens are prepared (for example, pathogens of infectious diseases, allergens or hormones);
  • the patient gives blood for analysis, from which the serum is released in the laboratory;
  • material for research is added to the wells of the ready-made kits, after which the antigen-antibody reaction occurs;
  • the remaining blood serum is removed, and detected antibodies are recognized using indicators.

An enzyme-linked immunosorbent assay is considered reliable. But in those cases when the wrong blood was taken for analysis, or the technique of the study was violated, or the person has latent systemic diseases, the results of an enzyme-linked immunosorbent assay may be false.

An enzyme-linked immunosorbent assay examines almost all thyroid hormones, tumor markers, and various types of infections.

Thyroid hormones include thyroglobulin (TG), thyroxine (T4), triiodothyronine (T3), free thyroxine (T4), free triiodothyronine (T3).

An enzyme-linked immunosorbent assay is normally considered if the following permissible norms of thyroid hormones are inherent:

  • thyroglobulin (TG) – permissible limits of 70 IU / ml;
  • thyroxine (T4) – 64-146 nmol / l (50-113 ng / ml);
  • triiodothyronine (T3) – 1,8-2,8 nmol / L (0,8-2,0 ng / ml);
  • free thyroxine (T4) – 11-25 pmol / l (10-27 pg / ml);
  • free triiodothyronine (T3) – 4,49-9,3 pmol / L (2,5-5,8 PG / ml).

In the case of a study of sex hormones, an enzyme-linked immunosorbent assay for women is considered normal if luteinizing hormone (LH) is released in the body within the following limits:

  • follicular phase of the cycle (from the first day of menstruation to the twelfth to fourteenth) – 2-14 mU / l;
  • ovulation phase of the cycle (from the twelfth day to the fourteenth day) – 24-150 mU / l;
  • the luteal phase of the cycle (from the fifteenth to sixteenth day to the beginning of the next menstrual period) – 2-17 mU / l.
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An enzyme-linked immunosorbent assay for men is taken if sex hormone is produced within 0,5–10 mU / L.

In the study of chronic gonadotropin (CG), reference values ​​depend on the gender of the person. In adult men and non-pregnant women, an enzyme-linked immunosorbent assay of blood is considered to be a CG level below 5 mU / ml. In pregnant women, the result depends on the gestational age and can range from 25-49000 mU / ml.

Enzyme-linked immunosorbent assay studies a variety of cancer indicators. These include the presence of prolactin, estradiol, progesterone, testosterone, steroid binding globulin (SSH) and other markers. But the interpretation of the result of an enzyme immunoassay of blood and the norms of these indicators should be carried out only by the attending physician.

In addition, this method diagnoses infectious (for example, rubella, measles, tuberculosis, herpes, syphilis, hepatitis, pseudotuberculosis) and various types of autoimmune diseases, and also establishes the person’s immune status. But all indicators and the results obtained should be decoded by a qualified specialist.

The analysis of the enzymatic phase of diagnosis is carried out using the method, which is called “colorimetry”. The fact is that not only the color of the material gives information about the infection, but also the color density resulting from chemical reactions. It is this indicator that determines the concentration of the pathogenic microorganism. If in the old fashion a manual diagnostic method is used, then a special calibration schedule is built to determine these indicators.

In modern laboratories, the manual method is rarely used today. For the analysis of ELISA, a special apparatus is used – a colorimeter, in which only research parameters are manually set, and then all work, including plotting, is performed automatically.

Many patients are interested in ELISA: what is it, what is the study done for. Enzyme-linked immunosorbent assay has been used relatively recently. Initially, antigenic structures were studied with its help, and it was carried out only for scientific purposes. Then scientists came to the conclusion that with the help of enzymes specific antibodies can be identified that occur in response to an ongoing disease.

Initially, this technique was used only by narrow-profile medical institutions, mainly at blood transfusion stations. Of particular importance is the ELISA method for detecting HIV infection.

Today, this method has a wide scope. Modern laboratories use it to diagnose:

  • tumors;
  • hormonal disorders;
  • infections
  • chronic or previous infectious processes;
  • helminths.

If an infectious process occurs in the body, then this type of diagnosis is considered the most optimal for determining the type of disease.

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History of the creation and development of IFA

This method of blood testing began to be used in practical medicine in the middle of the last century – somewhere in the 60s. Its initial goal was scientific research in the field of histology, which was limited to the search and study of the cellular antigenic structure of biological species. An ELISA blood test is based on the interaction of related antigens (AG) and specific antibodies (AT), with the formation of the complex “antigen-antibody”, determined by the enzyme.

Such a phenomenon prompted scientists to decide that the method can be used to recognize protein compounds of various classes formed in the blood serum when the pathogen enters the body. Due to their direct involvement in the functioning of the immune system, these compounds are called immunoglobulins (IG, Ig), and the discovery was the greatest breakthrough in laboratory diagnostics.

At the same time, they began to actively use this highly sensitive method only in the 80s, and it was available only in highly specialized medical institutions. The very first to get the opportunity to use enzyme immunoassay analyzers were blood transfusion centers and centers, venereological and infectious medical institutions. This was due to the rapid spread of the “plague of the XX century” – AIDS, and urgent adoption of diagnostic and therapeutic measures was required.

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The essence and scope of the method

Patients often ask: ELISA, what is it, how is it performed, and what is it for? Accessible about the method can be described by briefly describing its stages.

Preparatory stage. The laboratory doctor uses a special tablet in which 96 holes. The antigen of a specific pathogen is applied to the surface of each well.

Stage 1. A blood sampling is performed, which is then applied dropwise to the well. In the hole, a reaction is initiated between the antigen and the antibody in the blood.

Stage 2. In the well in full swing reaction with the formation of immune complexes. As a result, a substance of a certain color is formed. The color intensity depends on the amount of antibodies in the patient’s blood to each specific pathogen.

Stage 3. Evaluation of the result by photometry. For this, a special device called a “spectrophotometer” is used. With its help, the density of the material in the well and the control sample is compared. Further, the device generates a result by mathematical analysis.

The essence of the method and its types

The principle of the action of class A antibodies (IgA) is to protect the mucous membranes of the respiratory, stomach, intestines and urogenital organs. At the initial stage of the development of the disease, this type of immunoglobulin is not possible to identify. They appear only 14 days after the onset of the disease. As a rule, the main part of the immunoglobulins of this species is concentrated on the mucous membranes and only a small part (about 20%) circulates in the blood.

The main function of antibodies of this class is to identify, neutralize and destroy harmful microorganisms. As soon as the acute phase of the disease passes, the number of IgA class immunoglobulins decreases sharply. If after 8-10 weeks these markers are detected in the blood test, this indicates that the disease has become chronic.

The acute phase of any pathological process is characterized by high rates in the analysis of blood of class M immunoglobulins (IgM). Whether immunity to a particular disease has formed in the body can show class G (IgG). These markers are present in the blood 30 days after the disease. They will be traced in the analyzes for a long time, and in some cases until the end of life.

Immunoglobulin E (IgE) can detect helminths in the body. If the indicator of immunoglobulin D (IgD) according to the results of analyzes is higher than normal, then the patient is ill with bronchial asthma or other ailments associated with pathologies of connective tissues. In pregnant women, a slightly elevated class D antibody (IgD) is the norm.

ELISA method – what is it, what is the essence of this type of research? This and many other questions interest patients. The basis of this diagnostic method is the binding of the body’s immune cells to the antigens of the causative agents of the infection. The resulting complex is determined using a special enzyme.

To understand the principle of the ELISA method, you need to know how the antigen-antibody reaction proceeds. Antigen – a molecule of protein origin that is foreign to the body, which penetrates with the infection. Foreign blood particles that do not coincide in the group are also considered antigens. In the body, they provoke an immune response aimed at protecting against foreign substances.

The reaction to the presence of such immune complexes is carried out in the laboratory, using ready-made compounds to determine whether there are similar ones in the blood.

The essence of the ELISA method is quite simple, but due to the fact that a blood test is performed to detect many infections and diseases, there are several varieties of it. Each differs in the layout and scope. It can be direct or indirect ELISA. The direct method implies that immobilized antibodies that react with antigens are used. The main advantage of this method is that all processes can be automated, which means that diagnostics take a little time.

The indirect method implies that antibodies of a secondary nature are used. And on the solid phase, the antigen is immobilized. The analysis allows you to identify antibodies to various antigens. This helps to achieve a more accurate result, but the method is difficult.

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Svetlana Borszavich

General practitioner, cardiologist, with active work in therapy, gastroenterology, cardiology, rheumatology, immunology with allergology.
Fluent in general clinical methods for the diagnosis and treatment of heart disease, as well as electrocardiography, echocardiography, monitoring of cholera on an ECG and daily monitoring of blood pressure.
The treatment complex developed by the author significantly helps with cerebrovascular injuries and metabolic disorders in the brain and vascular diseases: hypertension and complications caused by diabetes.
The author is a member of the European Society of Therapists, a regular participant in scientific conferences and congresses in the field of cardiology and general medicine. She has repeatedly participated in a research program at a private university in Japan in the field of reconstructive medicine.