Analysis for syphilis ELISA - interpretation of the analysis. Norm and deviations

In connection with the development of cellular technologies, molecular biology, genetics, physics, chemistry and a number of other high-tech disciplines, new high-precision and high-tech methods are being introduced into everyday practice. These interdisciplinary trends affect both the field of medical knowledge and related areas of biological and biochemical problems. Over the past ten years, a clinical laboratory diagnostic method called enzyme immunoassay has become widespread and introduced into mass practice.

In general, technologies of immunological enzymatic and radiological reactions have been widely used in typing cells, cell cultures, and various tissues since the early 80s of the 20th century. However, these methods were very labor-intensive, not unified, not standardized, which precluded their use for diagnostic and treatment purposes on a mass scale. Such methods were used only by narrow, knowledge-intensive and highly specialized laboratories.

However, with the development of technology, microtechnology, and the production of various biopolymer materials, it has become possible to produce ready-made enzyme-linked immunosorbent diagnostic kits that can be used by laboratories of general medical institutions. ELISA is widely used to diagnose all kinds of infections (chlamydia, syphilis, cytomegalovirus, toxoplasmosis, herpes, etc.), both acute and chronic, as well as latent forms that occur without clinical symptoms. This method is also used to control chronic diseases. Let's try to figure out what kind of method this is and what principles underlie it?

Components of enzyme immunoassay - immune reaction and enzymatic reaction

The enzyme immunoassay, as the name suggests, consists of two different components - an immune reaction and an enzymatic reaction. The immune reaction produces the binding of biological molecules, elements of a cell or microorganism, which they are actually trying to detect, and the enzyme reaction allows you to see and measure the result of the immunological reaction. That is, the immune reaction is part of a complex technique that actually detects the desired microbe. And the enzyme reaction is that part of a complex technique that allows you to convert the result of the immune reaction into a form visible to the eye and accessible for measurement using routine chemical techniques. Based on this structure of the enzyme immunoassay method, we will analyze both of its parts separately.

Immune reaction, what is it? What is an antibody or antigen?

What is an immune response? What is an antigen?
First of all, let's look at what immune reactions are. Immune reactions– these are specific reactions of binding of an antigen to an antibody with the formation of an immune complex. What does it mean? On the surface of every cell of any organism there are special structures called antigens. Antigens in general are molecules that carry information about a cell (similar to information on a person’s badge, which indicates the basic data of that person).

Individual and species antigens – what are they? Why are these antigens needed?

Available individual antigens, that is, inherent only to this particular organism. These individual antigens are different for all people; there are some that are similar to each other, but still different. There are no two identical copies of individual antigens in nature!

The second main type of antigen is species antigens, that is, inherent in any specific type of living beings. For example, humans have their own species antigen, common to all people, mice have their own mouse species antigen, etc. On the surface of each cell, a specific and individual antigen is necessarily present.

The species antigen is used by cells of the immune system to recognize “friend or foe”.

How does antigen recognition occur?

The immune cell contacts the suspicious cell and makes an identification based on the individual antigen. In the memory of the immune cell, it is “recorded” what “its antigen” looks like. Thus, if the antigen of a suspicious cell matches the description “self antigen,” then this cell of the body’s own does not pose a danger. Then the immune cell “unties” and leaves. And if the antigen does not match the description of “self,” then the immune cell identifies this cell as “foreign,” and therefore potentially dangerous to the entire organism. In this case, the immune cell does not “get loose”, but begins to destroy the dangerous object. The accuracy of such immunological recognition is amazing - 99.97%. There are practically no mistakes!

What is an antibody, immune complex?
What is an antibody?

An antibody is a special molecule located on the surface of an immune cell. It is the antibody that binds to the antigens of the suspicious cell. Next, the antibody transmits information inside the cell, where recognition occurs, and receives a return signal of two types, “self” or “foreign.” When receiving a “self” signal, the antibody breaks the bond with the antigen and releases the cell.

What is an immune complex?
When the signal is “stranger,” the situation unfolds differently. The antibody does not break the connection with the antigen, but, on the contrary, by sending specific signals, causes “reinforcement”. Biologically, this means that other antibodies located in another part of the cell begin to move to the site where the danger signal is coming from and also form a bond between themselves and the captured antigen. In the end, the antigen turns out to be surrounded on all sides and firmly attached. This antigen + antibody complex is called immune complex. From this moment, the utilization of the antigen begins. But now we are not interested in the details of the antigen neutralization process.

Types of antibodies (IgA, IgM, IgG, IgD, IgE)
Antibodies are protein structures that, accordingly, have a chemical name, which is used as a synonym for the word antibody. So, antibodies = immunoglobulins.

There are 5 types of immunoglobulins (Ig), which bind to different types of antigens in different places of the human body (for example, on the skin, on mucous membranes, in the blood, etc.). That is, antibodies have a division of labor. These immunoglobulins are called by the letters of the Latin alphabet - A, M, G, D, E and are designated as follows - IgA, IgM, IgG, IgD, IgE.

In diagnosis, only one type of antibody is used, which is the most specific for the microbe being detected. That is, the binding of this type of antibody to the detected antigen always occurs. The most commonly used are IgG and IgM.

It is this principle of the immune reaction (the unique accuracy and specificity of recognition of the biological object being determined) that underlies the enzyme immunoassay. Due to the high accuracy of antibodies in recognizing antigens, the accuracy of the entire enzyme immunoassay method is also the highest.

Enzymatic reaction

Which reaction is enzymatic? What are affinity, substrate and product of a reaction?
Let's move on to consider the enzymatic reaction in the work of the enzyme immunoassay method.

What is an enzymatic reaction?

An enzymatic reaction is a chemical reaction in which one substance is converted into another by the action of an enzyme. The substance on which the enzyme acts is called substrate. And the substance that is obtained as a result of the action of an enzyme is called reaction product. Moreover, the peculiarity of the enzymatic reaction is such that a certain enzyme acts only on a certain substrate. This property of an enzyme to recognize “its” substrate is called affinity.

Thus, each enzyme carries out only one reaction specific to it. There are a great many known enzymes in the biological world, as well as enzymatic reactions. In enzyme-linked immunosorbent diagnostics, only a few enzymatic reactions are used - no more than 10. At the same time, such enzymatic reactions were chosen, the product of which is colored substances. Why should the products of an enzymatic reaction be colored? Because to calculate the concentration of a substance from a colored solution, there is a simple chemical method - colorimetry.

Colorimetry method - essence and principle

Colorimetry uses the measurement of the color density of a solution, and the concentration of the substance is calculated from the color density. In this case, a special device - a colorimeter measures the color density of the solution. In colorimetry, there are two possible options for the dependence of color density on the concentration of a substance - a directly proportional dependence or an inversely proportional dependence. With a directly proportional relationship, the higher the concentration of the substance, the more intense the color density of the solution. With an inversely proportional relationship, the higher the concentration of the substance, the lower the color density of the solution. Technically, this happens like this: several solutions with a known concentration of a substance are taken, the density of these solutions is measured, and a graph is constructed of the dependence of the concentration on the color density ( calibration chart).

Next, the color density of the solution, the concentration of which is determined, is measured, and from the calibration graph, the concentration value corresponding to the level of the measured color density of the solution is found. In modern automatic colorimeters, calibration is carried out only once, then the device itself builds a calibration curve, which remains in the device’s memory, and the measurement happens automatically.

The following enzymes are most often used in enzyme immunoassay: peroxidase, alkaline phosphatase, avidin.

How are immunological and enzymatic reactions combined in an enzyme immunoassay? Now we will move on to consider the enzyme immunoassay itself. What stages does it include and what happens during these reactions? Enzyme immunoassay can be direct and indirect.

Direct enzyme immunoassay - stages of implementation

In a direct enzyme immunoassay, antibodies to the detected antigen are used, combined with a specific label. This specific label is the substrate of the enzymatic reaction.

Attachment of antigens to the surface of the well and combination of antigen with antibody

How is direct enzyme immunoassay performed? Biological material is taken (blood, scrapings from mucous membranes, smears) and placed in special holes. The biological material is left in the wells for 15-30 minutes so that the antigens can adhere to the surface of the wells. Next, antibodies to the detected antigen are added to these wells. This means that when detecting antigens, for example, syphilis, antibodies against syphilis antigens are added. These antibodies are obtained industrially, and laboratories buy ready-made kits. This mixture of the test material and antibodies is left for some time (from 30 minutes to 4-5 hours) so that the antibodies can find and contact “their” antigen. The more in the biological sample of antigens, the more antibodies will bind to them.

Removing “extra” antibodies

As indicated, antibodies are also associated with a specific label. Since antibodies are added in excess, not all of them will bind to antigens, and if there is no antigen in the sample, then, accordingly, not a single antibody will bind to the desired antigen. In order to remove “extra” antibodies, the contents from the wells are simply poured out. As a result of this, all “extra” antibodies are removed, and those that have bound to the antigens remain, since the antigens are “glued” to the surface of the wells. The wells are rinsed several times with a special solution, which allows you to wash away all the “extra” antibodies.

Next, the second stage begins - the enzymatic reaction. A solution with enzyme is added to the washed wells and left for 30-60 minutes. This enzyme has an affinity for the substance (specific label) to which the antibodies are bound. The enzyme carries out a reaction that converts this specific mark (substrate) into a colored substance (product). Then, using colorimetry, the concentration of this colored substance is found. Since this specific label is associated with antibodies, it means that the concentration of the colored reaction product is equal to the concentration of antibodies. And the concentration of antibodies is equal to the concentration of antigens. Thus, as a result of the analysis, we receive an answer as to the concentration of the detected microbe or hormone.

This is exactly how direct enzyme immunoassay works. However, today indirect enzyme immunoassay is more often used, since the sensitivity and accuracy of indirect is higher than direct. So, let's move on to the indirect enzyme immunoassay.

Indirect enzyme immunoassay - stages of implementation

There are two stages in the indirect enzyme immunoassay. During the first stage, unlabeled antibodies to the detected antigens are used, and in the second stage, labeled antibodies are used to the first unlabeled antibodies. That is, it is not direct binding of an antibody to an antigen, but a double control: binding of antibodies to an antigen, followed by binding of second antibodies to the antibody + antigen complex. As a rule, antibodies for the first stage are mouse, and for the second - goat.

Fixation of antigens on the surface of the well and binding of the antigen to an unlabeled antibody
Just as for direct enzyme immunoassay, biological material is collected - blood, scrapings, smears. The biological material under study is introduced into the wells and left for 15-30 minutes for the antigens to adhere to the surface of the wells. Then unlabeled antibodies to the antigens are added to the wells and left for a period of time (1-5 hours) so that the antibodies bind to “their” antigens and form an immune complex ( First step). After that, “extra” unbound antibodies are removed by pouring out the contents of the wells. Wash with a special solution to completely remove all unbound antibodies.

Binding of labeled antibody to antigen + unlabeled antibody complex
After which they take the second labeled antibodies, add them to the wells and leave again for a while - 15-30 minutes ( second phase). During this time, labeled antibodies bind to the first - unlabeled ones - and form a complex - antibody + antibody + antigen. However, both labeled and unlabeled antibodies are added to the wells in excess. Therefore, it is necessary to again remove “extra” already labeled antibodies that have not bound to unlabeled antibodies. To do this, repeat the procedure of pouring out the contents of the wells and washing with a special solution.

Enzymatic reaction - formation of a colored compound
After that, an enzyme is added that carries out the reaction of converting the “label” into a colored substance. The color develops within 5-30 minutes. Then colorimetry is carried out and the concentration of the colored substance is calculated. Since the concentration of the colored substance is equal to the concentration of labeled antibodies, and the concentration of labeled antibodies is equal to the concentration of unlabeled antibodies, which, in turn, is equal to the concentration of the antigen. Thus, we obtain the concentration of the detected antigen.
This double control in the form of the use of two types of antibodies made it possible to increase the sensitivity and specificity of the enzyme immunoassay method. Despite the lengthening of the analysis time and the inclusion of additional stages, these losses are compensated by the accuracy of the result. That is why currently the vast majority of enzyme immunoassay methods are indirect enzyme immunoassays.

What diseases are detected by enzyme immunoassay?

Let's move on to consider what diseases and what biologically active substances are detected by enzyme immunoassay. Substances detected by enzyme immunoassay are presented in the table.

Hormones and markers of thyroid disease	Thyroid peroxidase (TPO)
	Thyroglobulin (TG)
	Thyroid-stimulating hormone (TSH)
	Thyroxine (T4)
	Triiodothyronine (T3)
	Free thyroxine (T4)
	Free triiodothyronine (T3)
Diagnosis of reproductive function	Luteinizing hormone (LH)
	Follicle stimulating hormone (FSH)
	Prolactin
	Progesterone
	Estradiol
	Testosterone
	Cortisol
	Steroid binding globulin (SBG)
	Alphafetoprotein (AFP)
Tumor markers	Chorionic gonadotropin (CG)
	Prostate-specific antigen (PSA)
	SA – 125
	SA – 19.9
	CYFRA-21-1
	M – 12 (SA – 15.3)
	MUC – 1 (M – 22)
	MUC1 (M – 20)
	Alveomucin
	K – chain
	L – chain
	Tumor necrosis factor (TNFα)
	γ – interferon
	Carcinoembryonic antigen (CEA)
Diagnosis of infectious diseases

ELISA is a modern laboratory test that searches for specific antibodies in the blood (or antigens) to specific diseases in order to identify not only the etiology, but also the stage of the disease.

1. search for specific antibodies to any infectious disease;
2. search for antigens of any infectious diseases;
3. study of the patient’s hormonal status;
4. screening for the presence of autoimmune diseases.

Like any method of laboratory diagnostics, ELISA has its advantages and disadvantages. The advantages of the method include:

1. high specificity and sensitivity of the method (more than 90%);
2. the ability to determine the disease and track the dynamics of the process, that is, comparing the number of antibodies in different time periods;
3. accessibility and speed of this research;
4. non-invasive method of collecting material, not research;

The disadvantage of the method is the fact that during the analysis it is possible to identify not the causative agent of the disease itself, but only the immune response to it (antibodies).

The essence of the ELISA method

There are several types of ELISA: direct, indirect, blocking method, competitive. However, in practice, the heterogeneous enzyme-linked immunosorbent assay, or ELISA, is most often used.

The basis of enzyme immunoassay is the immune reaction of an antigen and an antibody with the formation of an immune complex, resulting in a change in the enzymatic activity of specific marks on the surface of the antibodies.

Essentially, this process can be divided into several stages:

1. on the surface of the wells of the test system tablet there is a purified antigen of a specific pathogen. When animal blood serum is added, a specific reaction occurs between this antigen and the desired antibody;
2. Next, a special chromogen (conjugate labeled with peroxidase) is added to the well. An enzymatic reaction occurs, which results in the formation of a colored substance in the well of the plate. The intensity of its color depends on the amount of immunoglobulins (antibodies) contained in the animal’s serum;
3. Then the result is evaluated. Using a multichannel spectrophotometer, the optical density of the test material is compared with the optical density of control samples and the results are processed mathematically. The amount of antibodies in a patient directly depends on the height of the optical density of a given well.

It must be remembered: for each test system, individual indicators are developed to record the results, indicators of normality and pathology (“reference values”). This must be taken into account when assessing the results of each specific study.

It is incorrect to interpret the results of one laboratory based on the “reference values” of another laboratory. It is also incorrect to compare the results of different laboratories with each other.

When assessing the results for specific infections, the class of antibodies detected and their quantity are important. Not only the question of the etiology of the infection depends on this, but also the expected stage of the disease (acute, chronic), as well as the presence of an active infection (acute or exacerbation of chronic) at the time of examination.

What is the approximate time frame for the appearance of antibodies?

The earliest antibodies are IgM. They can be detected 1-3 weeks after possible infection, which characterizes the acute phase of the infectious process. The second situation for the appearance of IgM antibodies is an exacerbation of a chronic process. IgM circulates on average for about 3 months, then their amount gradually disappears. However, in some patients, trace amounts of IgM can be detected within 1-2 years after infection.

From the 4th week after infection, IgG antibodies begin to appear. With most infections, their titer gradually increases with a maximum at different times (on average after 1.5-2 months), then the titer remains at a low level and indicates immunity. In some diseases, IgG levels are not high.

Antibody detection options

• Isolated detection of IgM antibodies suggests the presence of a primary infection.
• Simultaneous detection of IgM and IgG in the blood is typical for primary infection in the previous 2-3 months, as well as during exacerbation of a chronic disease.
• Detection of isolated IgG may indicate both immunity to the disease and chronic infection. In the second situation, both the amount of antibodies (titer) and the change in this titer over time are important. Typically, studies are carried out at intervals of 2-4-6 weeks.

ELISA analysis is a modern laboratory diagnostic technique for a significant number of different diseases. The abbreviation stands for enzyme immunoassay. The essence of the technique is to determine the titer (activity) of antibodies.

The ELISA technique is currently gaining significant popularity. It is used in clinical medicine for the diagnosis of various pathologies, as well as in experimental studies that require accurate determination of the concentration of various compounds in the studied media.

The principle of the ELISA method

Enzyme immunoassay is an immunological reaction. It is based on the addition of specific antibodies
or antigens into the test medium (most often the blood being tested), followed by enzymatic determination of the concentration of the resulting antigen-antibody complexes. Based on the concentration of the complex, one can judge the level or activity of the compound being determined in the test medium.

Determination of the concentration of antigen-antibody complexes is usually carried out using special equipment using the chromatographic method.

Indications for use

ELISA analysis is carried out for various indications, the main ones in clinical medicine are:

• Diagnosis of infectious pathology with predominantly sexual transmission (STI), which includes chlamydia, mycoplasmosis, ureaplasmosis, trichomoniasis, while identifying specific antibodies to the infectious agent.
• Diagnosis of infectious diseases of various localization to determine the stage of the pathological process, primarily in the process of diagnosing parenteral viral hepatitis and HIV.
• Determination of hormone concentrations for the diagnosis of various pathologies of the endocrine system organs (endocrine glands).
• Determination of various compounds to diagnose the cause of intoxication of the body in case of poisoning, insect or snake bites.

For these medical indications, an ELISA blood test is performed. This technique is also actively used in experimental medicine during various clinical studies during the development of new medicines and vaccines for immunoprophylaxis.

How the research is carried out

A blood test using ELISA is carried out in a specialized laboratory. To carry it out, venous blood is first taken, usually from the cubital vein in a volume of 5-10 ml, which is then sent to the laboratory. On average, the test result can be obtained the very next day, which is an important point for promptly prescribing treatment after diagnosis of the disease.

How to prepare for ELISA

To obtain reliable research results using enzyme immunoassay, you should follow several simple preparatory recommendations, which include:

• The day before the test, you should stop eating fatty foods (meat, smoked meats) and alcohol.
• The material for the study must be submitted in the morning on an empty stomach.
• On the day of the study, it is advisable to avoid physical and psycho-emotional stress.
• Before the study, you should try not to smoke.

The majority of false-positive results of an enzyme-linked immunosorbent test are due to improper implementation of preparatory recommendations. This is in most cases associated with eating fatty foods, which lead to an increase in the concentration of triglycerides (fats) in the blood plasma, which reduce the specificity of the ELISA.

Decoding the results

A blood test for antibodies using ELISA has 2 modifications - qualitative and quantitative determination. At
In a qualitative determination of antibodies, the result can be positive (antibodies are detected, indicating the possible presence of a pathological process caused by an infectious agent) or negative (there are no antibodies, indicating the absence of an infectious process).

The absence of antibodies is not always a 100% indicator of the absence of an infectious process. This is due to the fact that after infection, antibodies are not formed immediately, but over a certain period of time (at least about 2 weeks). Therefore, to confirm the absence of infection, ELISA can be repeated after some time.

Quantitative ELISA is used to determine the titer (activity) of antibodies, as well as their classes. In most cases, to diagnose infectious diseases, antibodies of the IgG (immunoglobulin G) and IgM (immunoglobulin M) classes are determined, which are formed in the body at various intervals after infection, so deciphering the test result can have several meanings:

• An increase in IgM activity and the absence of IgG is evidence of recent infection and an acute course of the infectious process.
• An increase in the activity of IgM and IgG is an exacerbation of the infectious process during its chronic course and long-standing infection.
• High IgG activity and the absence of IgM is a chronic course of the infectious process against the background of a long-standing infection, after which more than six months have passed (the time required for the formation of IgG class antibodies).

In general, deciphering ELISA results for each infectious process has certain features. A more accurate determination of the presence of an infectious disease, as well as the stage of its course, is carried out by a doctor.

ELISA is currently the method of choice for diagnosing most infectious diseases. Based on the results of such a study, the doctor has the opportunity to establish an accurate diagnosis and determine the stage of the pathological process in order to prescribe subsequent adequate and effective treatment.

Modern diagnostic techniques make it possible to identify a particular disease in a laboratory using special tests. One of these is an enzyme-linked immunosorbent blood test, which can confirm a previously made diagnosis.

Enzyme immunoassay ELISA is one of the most effective and modern methods for identifying disorders associated with immune and hormonal imbalances, as well as oncological processes. During the test, antibodies produced when there is an infection in the body can be detected in the blood. Taking this nuance into account, the disease can be detected even at the earliest stage of its development.

What is the basis of the technique?

The results of ELISA analysis are based on obtaining chemical reactions to enzymes, which serve as special identification marks for recognizing antibodies. Consequently, during immunochemical reactions, antibodies begin to interact with certain antigens. All this gives grounds to assert that false results when donating blood to ELISA are minimal.

The study allows you to determine the number of immune cells, their properties, as well as the presence of the necessary antibodies

The result is considered positive when coloration of the solution is detected. The color indicates that the antigens are interacting with the antibody. If nothing like this happens, the result is negative.

An enzyme-linked immunosorbent test (ELISA) is carried out for a comprehensive assessment of the body's protective functions. During the study, the number and properties of immune cells and the presence of necessary antibodies are determined. An ELISA blood test is performed to diagnose infectious, hematological, autoimmune diseases, primary and secondary immunodeficiencies. Let's consider what an ELISA blood test is and what indications exist for conducting this study.

What it is

A blood test using the ELISA method is a laboratory method with which antibodies or antigens are determined in a blood sample. This study is used to determine the level of immunoglobulins, immunological complexes, and hormones.

Indications for analysis

The following indications exist for prescribing an ELISA blood test:

• diagnosis of sexually transmitted infections - ureaplasma, mycoplasma, chlamydia, trichomonas, syphilis;
• diagnosis of viral diseases - cytomegalovirus, herpes, hepatitis, Epstein-Barr virus;
• determination of hormone levels;
• diagnosis of oncological diseases;
• determination of immunodeficiency;
• diagnosing allergies;
• preoperative comprehensive examination before organ transplantation;
• assessment of the effectiveness of therapy.

Principle of the method

The principle of operation of the enzyme immunoassay method is based on the determination of specific antibody proteins in the blood - immunoglobulins. Immunoglobulins are produced by the human immune system when antigens (foreign microorganisms) enter the body. Such immune molecules bind to a variety of infectious pathogens in the body and neutralize them.

Immunoglobulins have an important characteristic – specificity. Thanks to this, they can bind to a specific antigen, forming an antigen-antibody complex. During an ELISA blood test, it is this complex that is determined qualitatively and quantitatively.

There are five classes of immunoglobulins. But usually three classes are defined - immunoglobulins A, M, G. These antibodies accumulate in the body at different times from the moment of infection.

• Immunoglobulins class M (IgM) appear in the blood very first on the fifth day from the moment of infection. They remain in the body for 5–6 weeks, then disappear from the bloodstream. IgM antibodies indicate an acute period of the disease or an exacerbation of the disease during its chronic course.
• Approximately 3–4 weeks after infection, immunoglobulins appear in the blood class G (IgG). They can exist in human blood for several months or even years. According to the interpretation of the ELISA blood test, if in two blood samples taken sequentially after two weeks, the amount of IgG immunoglobulins is increased, they speak of a current infection or reinfection - re-infection with the same infection.
• Immunoglobulins class A (IgA) can be detected by this research method 2–4 weeks after infection or exacerbation of an infectious disease. Of these, only 20% circulates in the blood, the rest are in the secretion of the mucous membranes. IgA antibodies disappear from the bloodstream 2–8 weeks after the destruction of infectious agents. The disappearance of these immunoglobulins means a cure for the infection. If, after the end of the disease, the presence of IgA antibodies in the blood is determined, it means that the disease has entered the chronic stage.

Preparing for analysis

To carry out a blood test using the ELISA method, human blood is most often used. But you can also examine the contents of the vitreous body, cerebrospinal fluid, and amniotic fluid.

A blood sample for testing is taken from the patient’s antecubital vein. It is recommended to donate blood on an empty stomach (at least 12 hours must have passed since your last meal). It is necessary to inform the doctor if the patient is taking medications, as some of them may change the test result. The reliability of the study results is affected by alcohol and drug use.

Decoding

The result form of this test indicates the positive (+) or negative (-) result of determining each class of immunoglobulins.

Let's consider the interpretation of a possible interpretation of the ELISA blood test.

• A negative result for IgM, IgG, IgA means lack of immunity to infection.
• A negative result for IgM, IgA and a positive result for IgG is post-infectious or post-vaccination immunity.
• Negative or positive result of IgG, IgA and positive result of IgM – acute infection.
• A positive result for IgM, IgG, IgA is an exacerbation of a chronic infectious disease.
• Negative IgM result and negative or positive IgG result, IgA – chronic infection.
• Negative IgM result and IgG, IgA are not detected - recovery.

Advantages of the method

The ELISA blood test has many advantages. The main ones can be identified:

• relatively high accuracy (sensitivity);
• the possibility of early diagnosis;
• the ability to monitor the dynamics of the infectious process;
• high level of unification, which allows for mass examinations;
• a short period of time required to obtain the analysis result;
• ease of use;
• automation of all stages of analysis;
• relatively low cost.

Flaws

The disadvantage of the ELISA method is that it sometimes gives false negative or false positive results. In addition to technical errors during the study, the cause of false results may be the patient’s rheumatoid factor, the presence of chronic diseases (in which antibodies are produced), metabolic disorders, or the use of certain medications.

• ascariasis;
• trichinosis - the analysis is carried out several times, the maximum level of antibodies is determined 4-12 weeks after infection;
• cysticercosis;
• taeniasis;
• fascioliasis – antibodies are detected in the acute stage of the disease;
• opisthorchiasis – differential diagnosis is carried out between the chronic and acute forms of the disease;
• giardiasis;
• visceral and cutaneous leishmaniasis;
• amoebiasis;
• toxoplasmosis.

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