The development of modern medicine in the world of diagnostics never ceases to amaze with its achievements, and now the doctor does not need to make assumptions about a probable diagnosis, relying only on indirect signs. The creation and introduction into the world of laboratory research of an enzyme-linked immunosorbent assay (ELISA) allows one to quickly and accurately determine not only the presence of a pathogen, but also many other characteristics of the disease.

History of the creation and development of ELISA

This method of blood testing began to be used in practical medicine back 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. The ELISA blood test is based on the interaction of related antigens (AGs) and specific antibodies (ABs), with the formation of an “antigen-antibody” complex determined by an enzyme.

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

However, this highly sensitive method began to be actively used only in the 80s, and it was available only in highly specialized medical institutions. The very first stations and blood transfusion centers, venereology and infectious diseases treatment institutions were able to use immunoenzyme analyzers. This was due to the rapid spread of the “plague of the 20th century” - AIDS, and urgent diagnostic and therapeutic measures were required.

Possibilities of the technique

The scope of application of the ELISA blood test is quite wide - at the moment it is impossible to imagine how complicated the search for the cause of many diseases would become. Such research is now used in almost all medical fields, even in oncology. Although it is difficult for the uninformed to understand, in some cases it was carried out, and it was possible to save the lives of patients by detecting the tumor in the early stages.

Important! ELISA is a blood test that shows markers characteristic of certain malignant processes, which makes it possible to detect the disease at a time when no other method can do it.

In modern diagnostic centers, laboratory examinations are represented not only by tumor markers - they are equipped with an impressive arsenal of panels for carrying out this diagnosis. With their help, you can identify many pathological conditions, such as hormonal imbalances and infectious processes of various origins.

In addition, conducting and interpreting an ELISA blood test will make it possible to track the effect of medications on the body of a sick person and even an animal. The latter is widely used in veterinary clinics, helping to maintain the health of our pets or feeders, ensuring a stable supply of meat, dairy products and eggs, which are essential in the diet.

Thus, as a result of collecting just a few milliliters of venous blood and diagnosing it using the ELISA method, the doctor, having described the research materials, will be able to determine:

• hormonal state, including biologically active substances of the reproductive and thyroid glands, as well as the adrenal glands;
• the presence of bacterial and viral infections (hepatitis B and C, syphilis, herpes, chlamydia, tuberculosis, myco- and ureaplasmosis, HIV, TORCH) and other diseases of this nature;
• signs of vital activity of pathogens of the pathological process, which ended with recovery and passed into the stage of formation of antibodies (immune response).

Such complexes are much easier to recognize and eliminate by immune cells. Residual effects in the form of antibodies in many cases are contained in the blood for life, which practically reduces the risk of re-infection to zero.

Types of immunoglobulins

There are several types of antibodies, and each of them is involved in the process of the immune response at a certain stage. For example, class M immunoglobulins (IgM) are the first to be formed in response to the entry of antigen into the body. Their highest rates are observed in the first days of the disease.

Types of immunoglobulins used in ELISA

Then the immune system releases class G IGs (IgG) into the plasma, which are responsible for the complete destruction of antigens and the recovery of the patient. Later, they continue to be in the blood, thereby preparing the immune system for repeated exposure to an identical pathogen. This is how vaccination works. When weakened antigens of pathological microorganisms are introduced, many immunoglobulins appear and remain circulating in the plasma.

The main objects of interest for laboratory diagnostics are Ig classes M, G and A. Based on the level of their concentration, you can determine the stage of the disease and find out what infectious diseases a person has had in his life. For example, you can check if there is a history of chickenpox or rubella. To find out whether a certain type of AT or AG is present in the patient’s body or the concentration of any hormone, the doctor does not need to prescribe multiple laboratory tests - it is enough to write out a referral for ELISA.

The essence of the technique

The research methodology is based on several options (direct and indirect - competitive and non-competitive) for performing the assigned tasks, each of them intended for specific purposes. This approach allows for a targeted search and, in the shortest possible time, identifying the cause of a particular pathology. To detect Ig of different class categories, a 96-well plate (polystyrene panel) is used, and sorbed recombinant proteins are located in its wells. They play the role of antigens, and at the initial stage they are in the solid phase.

When they enter a well with blood plasma, antigens or antibodies identify the object due to their direction and form a complex (AG - AT). This formation is fixed by an enzyme compound (conjugate), which will subsequently manifest itself as a changed coloration of the hole. ELISA is performed using specific test systems manufactured in specialized laboratories and equipped with a full set of reagents.

This analysis can be performed using washers and reading spectrometers, but they require manual labor. Of course, it is several times more convenient and faster for a laboratory technician to carry out all manipulations on fully automated instruments. When using them, laboratory staff are freed from a large amount of monotonous activity - washing, instillation and other routine work, but not all medical institutions can afford such expensive equipment

Therefore, many hospitals and diagnostic institutions continue to carry out ELISA the old fashioned way - using semi-automatic machines.

Interpretation of research materials is solely the responsibility of a laboratory diagnostics specialist - only he can tell the results about the specifics and subtleties of the course of the disease. In this case, the doctor must take into account the possibility of obtaining false negative or false positive answers.

Decoding materials

The result of high-quality immunoassay diagnostics should be an unambiguous conclusion - whether the desired microorganism was found or not in a given blood sample. Quantitative analysis will indicate the level of concentration and can be expressed in two ways - a numerical value or the number of “+” signs.

Analyzed indicators

The research process carefully examines the main immunoglobulins involved in the immune response, such as:

• IgM – detection of this class means the development of an acute form of an infectious disease. A negative result in the search for IgM can be either evidence of the absence of the desired pathogen or the transition of the disease to a chronic course.
• IgA is the definition of this class in the absence of IgM in most cases, a signal of a chronic or latent form of development of an infectious disease.
• IgM and IgA (simultaneous presence) - positive results for both types indicate the very peak of the acute form of the pathology.
• IgG – its presence indicates the transformation of the disease into a chronic form or recovery and the formation of immunity to the determined agent.

The appearance and accumulation of a certain class of IG occurs at different time stages. So, for example, IgM appears first, approximately 5 days after exposure to the pathogen. IGs remain in the blood for about 5–6 weeks and then gradually disappear. At this time, they are available for determination by ELISA. Approximately 3–4 weeks after the onset of the disease, IgG appears, which can subsequently remain for several months. But it is not always possible to detect them in analysis.

IgA is formed in the blood over a period of 2–4 weeks, with 20% of them contained in the serum, and 80% in the secretions of the mucous membranes. As a rule, these immunoglobulins disappear within 2–9 weeks, which indicates the destruction of the pathogen and the recovery of the patient. If ELISA still shows the presence of IgA, then this signals the transition of the process to a chronic form.

Options for analysis results

Depending on the data received, ELISA responses can be issued on a form in the form of a table with a complete list of all ATs and AGs and an indication of a positive or negative reaction. In certain situations, a quantitative value will be displayed - strongly positive, positive, weakly positive or negative. The second option indicates the amount of AT contained in the blood sample being studied.

Options for interpreting ELISA materials

In addition to the above values, the ELISA process examines another quantitative parameter - the AT avidity index, calculated as a percentage. It shows how long the disease lasts - that is, the higher the indicator, the longer it takes for the pathology to develop.

Alternative ELISA method

Enzyme immunoassay blood test is a fairly well-known and common diagnosis. Some people may have never heard of it, but there is one even less widely known version of this test, in which a non-blood sample is taken. This technique is called a stool occult blood test, and in many cases it allows you to avoid additional exhausting procedures, which are also accompanied by unpleasant sensations.

An ELISA test for occult blood (hemoglobin molecules) makes it possible to detect bleeding of the digestive system, even minor, signs of which, as they say, cannot be found in the patient’s stool with the naked eye. Enzyme immunoassay of occult blood in human feces in a short time can show peptic ulcers, polyposis, diverticulosis, tumors, which in the early stages are not accompanied by specific symptoms.

Today, thousands of varieties of enzyme-linked immunosorbent diagnostic test systems have been created, which provide the ability to detect ATs and AGs from a huge list of pathologies. Therefore, this analysis is used in almost all branches of medicine, for any age category. And its absolute harmlessness allows it to be used both during pregnancy and for diagnosing weakened patients.

For a comprehensive assessment of the state of the body (in particular its protective functions), an enzyme-linked immunosorbent test (ELISA) is prescribed. An ELISA blood test is performed to diagnose infectious, autoimmune, hematological pathologies, primary and secondary immunodeficiencies. In this article, we propose to consider in more detail what an ELISA blood test is, as well as what indications exist for its implementation.

Indications for prescribing a blood test using the ELISA method and the principle of its operation

As we have already noted, a blood test using the ELISA method is a laboratory test through which antigens or antibodies are determined in a blood sample. This analysis is used to detect the level of hormones, immunological complexes and immunoglobulins. There are the following indications for ELISA analysis:

• Diagnosis of allergies.
• Diagnosis of diseases of viral origin - Epstein-Barr virus, herpes, hepatitis, cytomegalovirus.
• Diagnosis of sexually transmitted infections - mycoplasma, ureaplasma, syphilis, trichomonas, chlamydia.
• Definition of immunodeficiency.
• Diagnosis of oncological pathologies.
• Evaluation of therapy effectiveness.
• Determination of hormone levels.
• Preoperative comprehensive examination.

The principle of operation of an enzyme immunoassay is based on a blood test for the presence of immunoglobulins (specific antibody proteins). Immunoglobulins are produced by the immune system when antigens (foreign microorganisms) enter the human body. These immune molecules bind to various infectious pathogens and neutralize them. An important distinguishing feature that immunoglobulins have is their specificity. Due to these characteristics, they can form an antigen-antibody complex by binding to a specific antigen. When performing an ELISA blood test, it is this complex that is determined quantitatively and qualitatively.

Human blood is often used to conduct this study. However, the contents of the vitreous body, amniotic fluid, and cerebrospinal fluid can be taken as material for analysis. The blood sample is usually taken from the patient's antecubital vein. It is recommended to donate blood on an empty stomach (at least 12 hours must pass since the last meal). If the patient is taking medications, it is necessary to inform the doctor, since some of them may affect the test result. The reliability of test results is also affected by drug and alcohol intake.

Interpretation of blood test for ELISA

The form for this analysis usually indicates a negative (-) or positive (+) result for calculating each class of immunoglobulins.

We propose to consider the interpretation of the probable interpretation of the ELISA blood test.

• IgG, IgA are not detected and the IgM result is negative - complete recovery.
• The result of IgM, IgA, IgG is negative – there is no immunity to infection.
• The result of IgG, IgA is positive and negative, as well as the result of IgM is positive - the presence of an acute infection.
• A positive IgG result and a negative IgA and IgM result means post-vaccination or post-infectious immunity.
• Positive or negative result of IgG, IgA and negative result of IgM – chronic infection.
• The result of IgG, IgM, IgA is positive - exacerbation of chronic infectious pathology.

In an enzyme immunoassay of blood, in addition to specifying the classes of antibodies, their quantitative indicators are indicated in the transcript. However, only the attending doctor provides an extensive explanation of them.

Strengths and weaknesses of this study

• Relatively low cost.
• Ease of use.
• Possibility of diagnosis at an early stage of the suspected disease.
• Relatively high accuracy of the obtained data.
• The short period of time required to obtain the research result.
• The ability to monitor the dynamics of the development of the infectious process in the body.
• High level of unification, making it possible to conduct mass surveys.
• Automation of all stages of research.

The disadvantage of the ELISA blood test is that it can, in fairly rare cases, give false-positive or false-negative results. Also, when conducting a study, in addition to technical errors, the cause of false results in a patient may be rheumatoid factor, the presence of chronic diseases (in which antibodies are produced), taking certain medications, or metabolic disorders.

• Giardiasis.
• Ascariasis.
• Cysticercosis.
• Amoebiasis.
• Trichinosis - the study is carried out more than once; the maximum level of antibodies is determined at 4-12 weeks after infection.
• Taeniasis.
• Opisthorchiasis - perform differential diagnosis between acute and chronic forms of the disease.
• Toxoplasmosis.
• Fascioliasis - in the acute stage of the disease, the presence of antibodies is determined.
• Cutaneous or visceral leishmaniasis.

So, we can summarize: an ELISA test for parasites is necessary to identify antigens (the waste products of parasites and their very presence), as well as antibodies (immunoglobulins). The specificity of this research method in identifying parasites, according to statistical data, is about 90%. Thanks to this analysis, the doctor can accurately determine the type of parasites, their total number, and also monitor the dynamics of the development of pathological processes thanks to the level of antibodies.

From time to time, doctors prescribe ELISA tests; not everyone knows what this is. ELISA has the following decoding - enzyme immunoassay of blood. Such a blood test helps to understand how the body fights infectious diseases and demonstrates the phase of the disease. Enzyme immunoassay helps in assessing the protective activity of the blood, identifying immunodeficiency in pathologies associated with infections, hormonal problems, etc.

The ELISA blood test works with material that is taken from a vein. In addition, the contents of the vitreous body, fluid from the spinal cord, and smears from the urethra or cervical canal are available for examination. For enzyme immunoassay ELISA, the fluid that surrounds the fetus can be taken from pregnant women.

In this case, blood can be directly tested for ELISA using different techniques. There is direct, indirect, competition and blocking. When the body is infected with some pathogenic agent, which is called an antigen, the immune system begins to produce specific antibodies, for example, to hepatitis. These antibodies are aimed at “dealing” with foreign agents. What are antibodies? These are special proteins that can interact with antigens and form immunological complexes called antigen-antibody. It is for the detection of these complexes that ELISA diagnostics is responsible. To detect an antigen, antibodies are added to the resulting blood sample or the reverse procedure is performed.

A positive ELISA result is based on the reaction of the immune system and enzymes. Under the influence of the first, infectious agents and cellular elements bind, the second helps to visualize the result of the first. The immune reaction involves an antibody and antigen combination. As a result of this process, an immune complex is formed. All cells have antigen on their surface. The immune cell captures the suspicious one, and the antigen, which is fixed on the surface, undergoes a comparison procedure with information that is “loaded” into memory. If there is a match in the description, then the cell returns home, but if not, then a connection occurs, the creation of which is responsible for the antibody that attaches to the surface.

The enzymatic reaction, meanwhile, allows substances to be transformed into new ones. The material is exposed to an enzyme. In this case, the enzymatic difference is ensured by different substrates. The product resulting from this reaction is sent for determination of the amount of pathogen, the determination of which is based on the density of the solution color.

Features of the method

An enzyme immunoassay blood test is prescribed when it is necessary to diagnose allergies and diseases of viral origin. There is also an ELISA test for syphilis and a number of other infections that are transmitted through unprotected sexual contact. This diagnosis is becoming increasingly popular compared to PCR. The fact is that PCR involves working with smears. Unlike PCR, ELISA results can be obtained from blood tests.

In addition, a blood test using the ELISA method can be prescribed when it is necessary to establish the presence of immunodeficiency, diagnose oncology, assess how effective treatment is, determine hormonal levels and undergo a preoperative examination as a whole.

If you compare ELISA studies, for example, with PCR, you can find a number of advantages. The main thing is the possibility of complete diagnosis even at the earliest stages of development. In addition, ELISA results help in determining the specific stage of the disease and the level of its development.

The ELISA test has a higher efficiency compared to PCR; in addition, it can be taken during pregnancy to detect STDs. Anyone who has taken this test can find out the concentration of TSH in the blood serum. This is very important to check what the reaction of the thyroid gland is, whether there are any malfunctions in its functioning.

Additional advantages, however, the polymerase chain reaction also has, is the speed of the study, which means quick results. Doctors also appreciate the accuracy of the results. If we are talking about STDs, then the level reaches 98 percent, as is the case with the TSH concentration.

Of course, there are some drawbacks. However, in this case we are talking about indirect features of the test. In particular, we are talking about the fact that it is impossible to exclude possible errors in determining standards. Sometimes a test taken by an absolutely healthy girl can show a false positive result, or a negative result in the opposite case. However, the classification of psychological research methods in most cases associates such shortcomings with improper preparation or violation of the technique with which the material was collected.

Execution Features

For ELISA analysis, in most cases, blood is donated. Before donating blood, it is important to fast for at least eight hours and avoid taking a number of medications that affect the test result. We are talking about antihistamines and hormonal drugs that affect the functioning of the thyroid gland. In addition, alcohol should be excluded for at least 24 hours. Ensure that you do not smoke at least one hour before donating blood. Distortion of the result is also possible when taking narcotic substances.

Before moving on to the transcript, it is worth mentioning what measurement methods are used for such a test. The test result will indicate antibodies or immunoglobulins Ig. They mean the very specific proteins that were discussed earlier. B-lymphocytes are responsible for their production as soon as viruses, bacteria or fungi enter the body. There are five types of immunoglobulins, designated by the Latin alphabet.

Their differences are associated with different molecular shapes and masses. They have different half-lives and are involved or not involved in infectious processes in different ways. The time frame within which they can be detected from the moment the infection occurs also varies.

If you classify immunoglobulins using molecular weight as a basis, then IgM has the highest indicators. A feature of this type of immunoglobulins is the inability to pass through the placental barrier. If IgM is detected in the test in a newborn child, we are talking about the presence of infection in the fetus.

The vast majority of human blood contains IgG immunoglobulins, the least of which is IgE. Speaking about work within the framework of infectious processes, special attention should be paid to options A, M, G. IgE acts as a marker of an allergic reaction. IgD is found only in the tissues of the lymph nodes and tonsils. This is important from the point of view of creating local immunity.

In addition, the analysis determines antigens. They are understood as substances of high molecular weight, which are known for their organic origin. In particular, we are talking about pathogens of infectious and other spectrum diseases. In addition, we also mean substances that signal various cell changes that are inevitable in a number of diseases. An immune complex is also indicated, which demonstrates an antigen-antibody complex that takes part in the immune process.

Typically, production times depend on the specific laboratory you contacted. Some laboratories are able to provide results within a day or two, others take a week. Delays may be due to the need to accumulate a certain amount of serum.

Impact on results and interpretation

Despite the fact that ELISA is considered one of the most accurate testing methods, errors still occur. The procedure for taking the material, improper transportation and storage of the material can affect the correctness of the results. Taking medications, as mentioned above, the presence of hidden diseases. Metabolic disorders or immunodeficiency will also not allow you to obtain the correct indicators. During the period of life up to one year, newborns may also have inaccurate indicators. This is due to the fact that maternal antibodies are present in the body.

Speaking of decoding, the analysis forms use a positive or negative sign to indicate the calculation results for each of the immunoglobulin classes. The following are likely options.

The absence of detected IgG, IgA and IgM indicates complete recovery. A negative result for components such as IgM, IgA, IgG means a lack of immunity to infection.

The combination of a positive and negative result for IgG, IgA in combination with positive IgM indicates the presence of an acute infection in the body. A positive IgG result combined with negative indicators for IgA and IgM corresponds to the post-vaccination period or the acquisition of immunity as a result of an infection.

The combination of a positive or negative result for IgG, IgA and a negative result for IgM indicates the presence of an infection in its chronic course. A positive result for three components: IgG, IgM, IgA indicates an exacerbation of an infection that was in a chronic form. In addition to directly clarifying the antibody classes, as part of deciphering the ELISA analysis, the doctor receives information about their quantitative indicators. It is important to emphasize that the attending physician should be responsible for decoding. The fact is that the combination of some components may lead him to think about the obtained false result, which will lead to retaking the test. Independent decryption in this case is useless.

(ELISA) is a method of testing blood in the laboratory, based on the search for special cells - antibodies to various diseases. The method allows not only to identify the pathogen, but also to determine at what stage the pathological process is. The latter is very important for the prognosis and further treatment of the patient.

Advantages and disadvantages of the method

Among all modern diagnostic methods, ELISA is the most innovative and technically accurate. Its main advantages are:

1. The ability to search for all existing antibodies to infectious diseases in the patient's blood.
2. High accessibility of the research method. Today, ELISA tests can be performed by any medium-sized laboratory.
3. Almost 100% specificity and sensitivity of the method.
4. The ability to search for antibodies and antigens, as well as establish the stage of the pathological process and track its dynamics, thanks to comparison of quantities.

This number of advantages over other tests completely overshadows the one and only drawback of the test: it is able to detect antibodies, but not the pathogen itself.

Key terms for assessing analysis

In order to understand what ELISA analysis is, what it is and how it is performed, you need to get acquainted with the basic terms used by specialists.

1. Antibody- a protein that is produced by cells of the human immune system (type B lymphocytes). They respond with a specific reaction to the entry of a foreign agent or substance into the body. Another name for antibodies is immunoglobulins; they belong to different classes: A, E, M, G. They differ from each other in mass, reaction speed, half-life and a number of other characteristics. Normally, human blood contains mainly class G immunoglobulins. If any infection occurs, the amount of immunoglobulins A and M increases sharply. Immunoglobulins E take part in allergic reactions.
2. Antigen- a foreign agent of organic origin and high molecular weight. Most often it represents pathogens or their biologically active substances.
3. The antigen-antibody complex, or immune complex, is the direct combination of a foreign substance and immunoglobulin, which gives rise to the development of an immune reaction.

The essence and scope of the method

Patients often have a question: ELISA analysis, what is it, how is it performed and what is it for? You can talk about the method in an accessible way by briefly describing its stages.

Preparatory stage. The laboratory doctor uses a special plate with 96 wells. The antigen of a specific pathogen is applied to the surface of each well.

Stage 1. Blood is drawn, which is then applied drop by drop to the well. The well initiates a reaction between the antigen and the antibody in the blood.

Stage 2. The reaction with the formation of immune complexes is in full swing in the hole. As a result, a substance of a certain color is formed. The intensity of the color 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 purpose, a special device called a spectrophotometer is used. It is used to compare the density of the material in the hole and the control sample. Next, the device generates a result through mathematical analysis.

Evaluation of results and purpose of ELISA

The interpretation of the result depends on several important nuances:

1. Optical density of the well.
2. Manufacturer of the plate with wells (test systems).
3. Laboratory in which the study was performed.

Given these nuances, you should never compare two results from different test systems or from different laboratories.

Another important point affecting the ELISA analysis is the so-called antibody avidity. This parameter characterizes the amount of antigen and the strength of the bond in the antigen-antibody complex. Its definition is based on the treatment of the immune complex with urea in order to resolve protein structures. This allows you to destroy weak bonds between antigen and antibody and leave only strong ones. The significance of the avidity study is that it can be used to determine the duration of infection. This information is extremely important for making a diagnosis in pregnant women.

A blood test using the ELISA method serves:

1. To search for various pathogen antigens.
2. To study hormonal levels.
3. For examination for the presence of autoimmune pathology.
4. To detect cancer markers.

Varieties of ELISA

ELISA analysis has the following types:

1. Indirect.
2. Straight.
3. Competitive.
4. Blocking method.

But in fact, today only a method called ELISA (enzyme linked immunosorbent assay) is used. It is based on the above-described reaction of the formation of an antigen-antibody complex with a change in color on the surface of the well.

The quantitative ELISA blood test itself deserves special attention. This is not a type of analysis, but a way of evaluating results. Thanks to it, the number of antibodies is calculated and their classes are determined. The result depends on the optical density of the sample, the test system on which the ELISA analysis was performed, as well as on the laboratory.

Diseases detected by ELISA

ELISA is a blood test that can detect a huge number of different infectious diseases. Moreover, both viral and bacterial diseases are detected with equal accuracy. For example, using the formation of immune complexes, one can prove the presence of antigens of pathogens of the following diseases:

In addition, ELISA allows you to detect:

1. Cancer markers - TNF (tumor necrosis factor), PSA (prostate-specific antigen), CEA (carcinoembryonic antigen), CA-125 (ovarian tumor marker)
2. The pregnancy hormone is hCG (human chorionic gonadotropin).
3. Reproductive system disorders: hormones of the female and male reproductive systems.
4. Pathology of the thyroid gland.

It is important to mention that the ELISA test for HIV today is the main way to diagnose this dangerous disease.

Material for ELISA and sampling technique

To perform ELISA, blood is drawn from the patient on an empty stomach. Next, serum is obtained from the blood, which is directly used for analysis. In addition, ELISA can be performed on cerebrospinal fluid (CSF), cervical mucus (cervix), amniotic fluid, and even vitreous fluid (eyeball).

Before donating blood, the patient is warned that he should not take any medications, and treatment with antibiotics and antiviral drugs is recommended to be completed at least two weeks before blood collection.

Deadlines for receiving and decoding results

The time it takes to receive an answer from the laboratory does not depend on the speed of its work, but on what stage the disease is at and what antibodies have already appeared in the blood. So, for example: immunoglobulins M appear approximately 2 weeks after taking blood for analysis and mean that the process is at the stage of primary infection or an exacerbation of chronic infection has occurred. At the same time, antibodies of classes M and G appear during primary infection. Moreover, the latter can be detected after 4 weeks.

IgA appears after 2-3 weeks, either alone or together with M, indicating an acute infection, or together with G, indicating a chronic process.

Such different periods for the appearance of antibodies in the blood will force the patient to wait a long time for the result. It is acceptable to wait more than a month after the ELISA test is performed. Deciphering and interpretation by a doctor also takes a certain period of time.

The list of standard diagnostic measures used for infectious diseases includes enzyme immunoassay. If the ELISA is positive for syphilis, do not immediately panic.

Let us take a closer look at the features of this research technique and the principles for interpreting the results obtained in different categories of patients.

Enzyme immunoassay is one of the most common methods for diagnosing infectious diseases. It belongs to the category of treponemal tests, that is, it can be used to determine the presence of the causative agent of syphilis - treponema pallidum - in the patient's body.

Using the ELISA method, syphilis is detected by detecting antibodies to treponema. They are contained in the patient’s blood, and their type and quantity depend on the stage and form of the disease, which allows one to obtain important information about the current state of human health.

Advantages and disadvantages

ELISA is very often prescribed for suspected syphilis or other infectious diseases. This is due to the fact that the analysis allows us to identify the exact type and stage of the disease, and its reliability remains at a high level - the probability of error based on the results of multiple studies is only 1%, the primary ELISA has an accuracy of about 90%.

The use of high-quality reagents and modern equipment allows us to maximize the accuracy of indicators.

In general, the advantages of the method are:

1. High accuracy of results. The likelihood of receiving false data is very low.
2. Minimizing the human factor of influence. Modern equipment for conducting ELISA eliminates human influence on the results of the study due to automation of the process.
3. Identification of specific antibodies. It is impossible to confuse antigens of one type with others, so the analysis shows the exact result for a specific diagnosis.
4. Recording the slightest deviations from the norm. Even the smallest concentration of pathological agents will not go unnoticed.

We should not forget about the weaknesses of this method. ELISA has the following disadvantages:

1. High price. The high cost is due to many factors, in particular, the need for good equipment, high-quality reagents and specialists with a sufficient level of training.
2. The need for a preliminary diagnosis. You need to know which antigens to look for, since without additional data it will be impossible to make an accurate diagnosis.
3. Probability of a false positive result. Certain body conditions and other factors may distort the final data.

Indications for use

A doctor may prescribe an enzyme immunoassay to diagnose not only syphilis, but also a number of other infectious diseases.

If we consider the situation directly with treponema infection, the reason for examination may be:

• the appearance of external symptoms of the disease (chancres, syphilitic rash, gummas, etc.);
• significant decrease in immunity;
• detection or suspicion of syphilis in a sexual partner, loved ones and family members;
• positive reaction during other tests;
• identifying other diseases that may be associated with syphilis;
• a person’s personal wish to undergo examination.

Methods of carrying out

ELISA can be carried out in different ways. In each specific case, the most suitable option is selected.

First of all, there is a division of methods into:

1. Qualitative. The presence of an infection or virus in the patient’s body is detected.
2. Quantitative. Determines the concentration of antibodies to a pathogenic agent in the human body, which indicates the stage and intensity of the development of the disease.

There is also a classification of methods for conducting ELISA based on the principle of reproducing the required reaction.

There are 3 options:

1. Straight. The labeled antibodies are injected into the provided blood samples.
2. Indirect with antigens. The sorbed antigens are first placed in the cells of a polystyrene plate intended for ELISA. Then viral antibodies are added to them, which provokes the formation of immune complexes necessary for further evaluation of the results.
3. Indirect with antibodies. This method is often used for sexually transmitted diseases. It involves preliminary absorption of antibodies, only then antigens are added to the tablet.

Material collection rules

In order to reduce the risk of receiving unreliable results, it is necessary to correctly donate blood for analysis.

Before taking the ELISA test, you must comply with some restrictions:

• avoid intense physical and emotional stress;
• stop smoking and drinking alcohol for at least 1-3 days;
• for a few days you need to switch to proper nutrition;
• It is advisable for women to control the phase of the menstrual cycle, since hormones can distort the results;
• the last meal should be 8-10 hours before blood donation;
• 10 days before taking medications that may affect the results of the study are excluded.

For ELISA, venous blood is taken from the ulnar vein; it must be donated in the morning on an empty stomach. In general, standard rules for preparing for venous blood collection apply. Depending on the presence of which disease is being tested, additional requirements for the preliminary preparation of the patient may be introduced.

Methodology

The instructions for performing ELISA are quite simple:

1. The patient's blood is taken from a vein.
2. The taken material is prepared and divided into samples on a special fine-mesh pallet.
3. Antigens are mixed with antibodies according to the chosen method.
4. The reaction is assessed. The samples are compared with control samples, and the results are assessed qualitatively and quantitatively.
5. The data is entered into a special table with quantitative indicators attached (total antibodies).
6. The attending physician interprets the results. If necessary, appropriate treatment is prescribed.

After the examination, the patient is given a document with the results. It looks like a table with corresponding symbols opposite each type of immunoglobulin at the intersection with the names of infectious diseases.

Decoding

Only a specialist will be able to correctly decipher the test results. It is difficult to figure out on your own, for example, what the ELISA result k = 1 4 means. Syphilis can also occur in different forms, which is also reflected in the final data.

The results indicate 3 types of immunoglobulins:

1. IgM. Allows you to determine the duration of infection with syphilis. A positive result indicates an exacerbation of the disease. Their absence may indicate remission of chronic pathologies or a latent form of the disease.
2. IgA. Indicates a disease that has been more than a month since infection. It is also a sign of the acute phase of the disease, both in ordinary pathologies and in advanced chronic ones.
3. IgG. It is a sign of the peak period of the disease, that is, its exacerbation. With syphilis, a positive reaction appears some time after treatment. In some types of diseases it may be a sign of developed immunity.

These substances are produced by the body in a certain sequence, which is an additional sign of the disease. Qualitative tests only determine the presence of immunoglobulins in the blood of each type.

This is reflected in a change in the color of the materials involved in the analysis. Quantitative indicators are auxiliary; they more accurately describe the situation. The ratio of antigens and antibodies indicates the severity of the disease and the intensity of the body's response.

What to do

If the patient really has syphilis, a positive ELISA is absolutely always detected; it is impossible not to notice the presence of treponemes during such a study. Do not despair, the disease is highly treatable, especially in the initial stages.

What to do if the test results are positive:

• according to the doctor's indications, undergo additional examinations;
• complete a course of antibiotic therapy according to the chosen regimen;
• focus your efforts on strengthening your immune system;
• inform your sexual partner about the disease;
• in the future, regularly undergo preventive diagnostics until deregistration at the dispensary (after 5 years in the absence of positive test results).

There is no need to put off taking sick leave and be afraid of publicizing the results. The diagnosis is encrypted and remains secret; only if there is a threat of infection to other people, it is necessary to inform relatives and sexual partners about the problem so that they undergo the required examinations.

False positive result and its causes

Sometimes the results of other tests and ELISA are recorded as false positive for syphilis. That is why it is recommended to carry out 2 - 3 auxiliary methods and repeat the enzyme immunoassay after some time.

Such inaccuracies are rare; they are mainly due to the following factors:

• pregnancy;
• chronic diseases;
• recent vaccination;
• injuries.

False-positive results are divided into acute and chronic, depending on the nature of the factor that provoked them.

The main ones are presented in the table:

Title and photo	Short description
Pregnancy	The fetus and the father's genetic material are regarded as foreign agents.
Acute form
Infection	Immunoglobulins are produced to fight the disease.
Injury	The body reacts with an inflammatory process, and concomitant infection may occur.
Intoxication	Occurs when poisoned by toxic substances or the penetration of certain pathogenic microorganisms.
Heart attack	Acute heart problems place a significant burden on the body and cause a number of desensitizing reactions.
Vaccination	The introduction of the vaccine affects the production of immunoglobulins.
Chronic form
Tuberculosis	An advanced form of tuberculosis exhibits a similar reaction.
Liver pathologies	The functioning of the entire body is disrupted.
Autoimmune diseases	With such failures, the production of immunoglobulins may be unfounded by the presence of antibodies.
Connective tissue diseases	They are predominantly genetic pathologies and sometimes “confuse” the results of examinations.
Age-related changes	In older people, the immune system malfunctions, and there are many chronic diseases.

If you have such health problems, a test for syphilis may show a positive result, but this is only a consequence of the body producing proteins to fight the disease. However, ELISA recognizes them as antigens.

In a healthy child up to one and a half years old, false positive ELISA results may be observed if the woman was infected with syphilis during pregnancy. Before this age, the blood has not yet had time to completely renew itself, so mother’s antibodies may be present in it. An exception is the situation with the detection of IgM immunoglobulins.

You can find out more information about the features of enzyme immunoassay and the methodology for its implementation by watching the video in this article.