Immunoassay Blood Test In Parasitology

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Immunoassay Blood Test In Parasitology
Immunoassay Blood Test In Parasitology

Video: Immunoassay Blood Test In Parasitology

Video: Immunoassay Blood Test In Parasitology
Video: Immunodiagnostic Methods – Immunology | Lecturio 2024, March
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An enzyme-linked immunosorbent assay is performed when difficulties arise with the diagnosis, if the patient has a hereditary predisposition to certain diseases, in order to assess the effectiveness of treatment. ELISA is a modern laboratory test that helps to identify specific antibodies in the blood for certain diseases. The method is highly specific and sensitive.

The content of the article:

  • 1 Immunoassay
  • 2 Basic concepts and principle of the enzyme immunoassay method
  • 3 Different classes of antibodies IgG, IgM, IgA

    • 3.1 IgM antibodies
    • 3.2 IgG antibodies
    • 3.3 IgA antibodies
  • 4 Advantages of the method
  • 5 Disadvantages of the method
  • 6 Indications for appointment and detectable diseases
  • 7 The analyzed biomaterial and features of its collection
  • 8 Timing of readiness of ELISA results
  • 9 Interpretation of enzyme immunoassay
  • 10 Possible ELISA results
  • 11 In conclusion

Linked immunosorbent assay

What is ELISA analysis
What is ELISA analysis

The analysis reveals antigens characteristic of certain pathogens and antibodies to them. The enzyme-linked immunosorbent assay is based on the reaction of interaction of an antigen with a specific antibody, as a result of which a complex is formed, which has a special label in its composition, which changes the color of the sample under the action of the reagent.

The intensity of the staining makes it possible to judge the presence of antibodies or antigens characteristic of a particular infection, and already with the help of the equipment, their quantity is determined. Antigens are foreign substances that cause an immune defense reaction in the body - specific proteins (immunoglobulins) are produced.

Each pathogen has its own set of antigens, and the immune response to them is also specific. The main material for analysis is blood from a vein.

An enzyme-linked immunosorbent assay makes it possible to identify with high accuracy latent diseases at an early stage, inform the doctor about the patient's general condition and the risks of developing pathologies, about the state of reproductive health.

An analysis is carried out to diagnose viral diseases: herpes, hepatitis, cytomegalovirus, Epstein-Barr virus, etc., sexually transmitted infections: gonorrhea, ureaplasma, chlamydosis, mycoplasma, Trichomonas, syphilis, to determine hormonal levels, diagnose cancer and immunodeficiency, detection and treatment of allergies. For the analysis, in addition to blood, you can also take cerebrospinal fluid, amniotic fluid, and the contents of the vitreous body.

The analysis assumes the use of a group of ELI tests:

  • ELI-B test, which allows to make a conclusion about the state of the immune system;
  • ELI-Dia-test, which determines the state of the endocrine system. With its help, diabetes of the first and second types is diagnosed;
  • ELI-N-Complex-12, which informs about the state of the peripheral and central nervous systems;
  • ELI-Ankor-test-12, an analysis that assesses the state of the heart and blood vessels, assesses the risk of developing a stroke, heart attack;
  • ELI-Viscero-16 is done to assess the general condition of the patient. This test provides diagnostics for 16 indicators: intestines, nervous system, myocardium, kidneys, immune system, liver, stomach, etc.;
  • ELI-P-complex-12 is made to assess the reproductive capacity of the body;
  • ELI-GIT-12 - an analysis that assesses the state of the gastrointestinal tract and makes it possible to foresee the risk of developing pathologies;
  • ELI-HCG-APS test, reveals reproductive health disorders.

Basic concepts and principle of the enzyme immunoassay method

The enzyme-linked immunosorbent assay (ELISA) is a laboratory diagnostic method based on the antigen-antibody reaction, which allows you to identify protein substances (including enzymes, viruses, bacterial fragments and other components of biological fluids). To understand how the enzyme immunoassay works, let's try to understand the essence of the "antigen-antibody" reaction. An antigen is a molecule foreign to the body, usually of protein origin, which can enter the human body together with an infectious agent.

Particles of someone else's blood (if it does not match our group) are also antigens. In the body, antigens are capable of causing an immune response aimed at protecting the integrity of the internal environment from foreign substances. Therefore, our body synthesizes special substances - antibodies (immunoglobulins), capable of connecting with antigens according to the principle of "key to lock", binding them into an immune complex (this process is called the "antigen-antibody" reaction).

Linked immunosorbent assay. Such immune complexes are more easily recognized and destroyed by immune cells. There are several types of antibodies, each of which comes into action at a specific stage in the immune response. Thus, immunoglobulins of class M (IgM) are synthesized first in response to the penetration of an antigen into the body.

The content of these antibodies is highest in the early days of the infectious process. Following them, the immune system releases class G immunoglobulins (IgG) into the blood, which help destroy antigens until the infection is completely defeated, and also continue to circulate through the vessels in the future, providing immunity to re-infection.

Vaccination is based on this phenomenon: thanks to vaccinations containing weakened antigens of microbes and viruses, a large amount of IgG appears in our blood, which, upon contact with a real threat, quickly suppress the infection - before it harms health. There are also class A immunoglobulins (they are found in large quantities in the mucous membranes, protecting the "approaches" to the body), E (fighting parasitic infections) and others.

What is ELISA analysis
What is ELISA analysis

In laboratory diagnostics, the objects of interest are most often IgM, IgG and IgA: by their concentration it is possible to assess at what stage the infectious process is, and also to find out whether a person has ever been ill with one or another ailment (for example, rubella or chickenpox). How do you know which antigens or antibodies are present in the human body? When a doctor suspects that a certain infection is the cause of the disease, or wants to measure the concentration of a certain hormone, he prescribes an enzyme immunoassay for the patient.

The "antigen-antibody" reaction can be reproduced in laboratory conditions: use ready-made antibodies or antigens to determine whether the corresponding compound is present in the sample under study. First, you need to get a sample of biological fluid - usually blood serum. The laboratory uses plastic plates with wells that already contain purified antigens of the suspected pathogen (or antibodies if the task is to search for an antigen).

Samples are placed in wells where - or not - immune complexes are formed. If the "meeting" has taken place, a particular dye enters into an enzymatic reaction with the combined molecule, which allows drawing a conclusion about the analysis results using an instrumental optical density assessment.

ELISA is qualitative and quantitative. In the first case, an unambiguous answer is implied: the desired substance is either found or not found in the sample.

In the case of quantitative analysis, a more complex chain of reactions makes it possible to assess the concentration of antibodies in human blood, which, in comparison with the results of previous tests, will answer the question of how the infectious process develops. Interestingly The precursor to enzyme immunoassay was radioimmunoassay, which used labeled antibodies and antigens to identify a successful reaction. Since carrying out such diagnostics posed a potential threat to the health of the laboratory staff, the scientists started looking for a safe alternative to “stain” the samples. So in 1971 the IFA was invented.

Various classes of antibodies IgG, IgM, IgA

What is ELISA analysis
What is ELISA analysis

The enzyme-linked immunosorbent assay detects antibodies of infections belonging to different classes of Ig (G, A, M). Antibodies to the virus, in the presence of infection, are determined at a very early stage, which ensures effective diagnosis and control of the course of diseases. The most common methods for diagnosing infections are tests for IgM antibodies (acute phase of infection) and IgG antibodies (resistant to infection). These antibodies are determined for most infections.

However, one of the most common tests - hospital screening (tests for HIV, syphilis and hepatitis B and C) does not differentiate the type of antibodies, since the presence of antibodies to the viruses of these infections automatically suggests a chronic course of the disease and is a contraindication, for example, for serious surgical interventions. Therefore, it is important to refute or confirm the diagnosis.

Linked immunosorbent assay. A detailed diagnosis of the type and amount of antibodies in a diagnosed disease can be done by passing an analysis for each specific infection and type of antibodies. Primary infection is detected when a diagnostically significant level of IgM antibodies is detected in a blood sample or a significant increase in the number of IgA or IgG antibodies in paired sera taken with an interval of 1-4 weeks.

Reinfection, or re-infection, is detected by a rapid rise in IgA or IgG antibody levels. IgA antibodies are higher in older patients and more accurately diagnose current infection in adults.

Past infection in the blood is defined as increased IgG antibodies without an increase in their concentration in paired samples taken with an interval of 2 weeks. At the same time, there are no antibodies of the IgM and A classes.

IgM antibodies

What is ELISA analysis
What is ELISA analysis

Their concentration rises soon after the disease. IgM antibodies are detected as early as 5 days after its onset and reach a peak in the interval from one to four weeks, then decline to diagnostically insignificant levels within several months, even without treatment. However, for a complete diagnosis, it is not enough to determine only class M antibodies: the absence of this class of antibodies does not mean the absence of the disease. There is no acute form of the disease, but it can be chronic.

IgM antibodies are of great importance in the diagnosis of hepatitis A and childhood infections (rubella, whooping cough, chickenpox), easily transmitted by airborne droplets, since it is important to identify the disease as early as possible and isolate the sick person.

IgG antibodies

The main role of IgG antibodies is the long-term protection of the body against most bacteria and viruses - although their production occurs more slowly, the response to an antigenic stimulus remains more stable than that of antibodies of the IgM class.

Linked immunosorbent assay. IgG antibody levels rise more slowly (15-20 days after the onset of the disease) than IgM, but remain elevated for longer, and therefore may show a long-standing infection in the absence of IgM antibodies. IgG levels can be low for many years, but with repeated exposure to the same antigen, IgG antibody levels rise rapidly.

For a complete diagnostic picture, it is necessary to determine IgA and IgG antibodies simultaneously. If IgA result is unclear, confirmation by IgM determination. In the case of a positive result and for an accurate diagnosis, a second test, made 8-14 days after the first, should be checked in parallel to determine the increase in IgG concentration. The results of the analysis should be interpreted in conjunction with the information obtained in other diagnostic procedures.

IgG antibodies, in particular, are used to diagnose Helicobacter pylori, one of the causes of ulcers and gastritis.

IgA antibodies

They appear in serum 10-14 days after the onset of the disease, and at first they can even be found in seminal and vaginal fluids. IgA antibody levels usually decline by 2-4 months after infection if treatment is successful. Upon reinfection, the IgA antibody level rises again. If the IgA level does not drop after treatment, then this is a sign of a chronic form of infection.

Method advantages

The indisputable advantages of ELISA are the high sensitivity and specificity of the method. Sensitivity is the ability to recognize the target substance, even if its concentration in the sample is low. Specificity, on the other hand, implies the accuracy of the diagnosis: if the result is positive, it means that exactly the antibody or antigen that was assumed was found, and not some others.

Enzyme-linked immunosorbent assay has largely replaced the "gold standard" of microbiology - a bacteriological diagnostic method, during which, in order to identify a pathogen, it was required to isolate it from the body, and then grow the culture in a culture medium in a test tube for several days. All the time, while the analysis was being carried out, the doctors were forced to treat the patient "blindly", guessing about the origin of the microorganism by the symptoms of the disease.

Determination of IgM using ELISA allows you to make an accurate diagnosis in the first days of the disease. The high degree of manufacturability of enzyme immunoassay minimizes the influence of the human factor, which reduces the likelihood of error. Most of the ELISA test kits and reagents used in modern laboratories are manufactured in an industrial environment, which guarantees an accurate result.

Disadvantages of the method

What is ELISA analysis
What is ELISA analysis

Unfortunately, to carry out ELISA, you need to know what exactly to look for: the analysis technique implies that the doctor has an assumption in advance about the nature of the disease. Therefore, it makes no sense to prescribe such a test in the hope of accidentally "guessing" the diagnosis. In the case of diagnosing infectious diseases, an enzyme immunoassay cannot find the pathogen and determine its specific properties: it only indicates the presence of antibodies in the patient's blood, indirectly indicating the presence of a foreign microorganism in the human body.

ELISA is an extremely accurate, but not cheap method, so you need to use it wisely, and a qualified doctor should interpret the results.

Indications for appointment and detected diseases

It is impossible to cover the full list of indications for ELISA. The most common purposes of the analysis are: Diagnosis of acute and chronic infectious diseases:

  • IgM and IgG to viral hepatitis A, B, C, E, as well as hepatitis B and C antigens;
  • IgG to HIV; Ig M and IgG to cytomegalovirus infection;
  • Ig M and IgG to Epstein-Barr virus; Ig M and IgG to herpes infections;
  • Ig M and IgG to toxoplasmosis;
  • Ig M and IgG to measles, rubella, salmonellosis, dysentery, tick-borne encephalitis and other diseases;
  • IgG to parasitic diseases;
  • Ig M and IgG to sexually transmitted infections;
  • IgG to Helicobacter pylori infection.

General assessment of indicators of human immunity and markers of some autoimmune diseases. Identification of oncological markers (tumor necrosis factor, prostate-specific antigen, cancer-embryonic antigen and others). Determination of the content of hormones in the blood serum (progesterone, prolactin, testosterone, thyroid stimulating hormone and others).

The analyzed biomaterial and features of its collection

What is ELISA analysis
What is ELISA analysis

The main biomaterial for ELISA is blood serum: in the laboratory, a blood sample is taken from the patient from a vein, from which the shaped elements that complicate the analysis are further removed. In some other cases, cerebrospinal fluid, amniotic fluid, smears of mucous membranes, etc. are used for analysis.

In order to avoid distortions in the results, it is recommended to donate blood on an empty stomach, and two weeks before the study (if the goal is to diagnose chronic, latent infectious diseases), it is necessary to stop taking antibiotics and antiviral drugs. Terms of readiness of ELISA results If you have the necessary reagents and good organization of the laboratory, you will receive the test result within 1–2 days after blood collection. In some cases, if an emergency response is required, this period can be reduced to 2-3 hours.

IFA results are ready

If you have the necessary reagents and good organization of the laboratory, you will receive the test result within 1–2 days after blood collection. In some cases, if an emergency response is required, this period can be reduced to 2-3 hours.

Decoding of enzyme immunoassay

The result of a high-quality ELISA will be an unambiguous verdict: the desired substance is either found or not found in the sample. If we are talking about quantitative analysis, then the concentration can be expressed as a numerical value or a certain number of "+" signs (from one to several).

Analyzed indicators:

  • IgM - the presence of this class of immunoglobulins indicates an acute infectious process in the body. The absence of IgM can indicate both the absence of a specific pathogen in the body, and the transition of the infection to the chronic stage.
  • IgA with a negative IgM test most often indicates a chronic or latent infection. IgM and IgA (joint presence) - two positive results indicate the height of the acute phase of the disease.
  • IgG speaks either about the chronicity of the disease or about recovery and the development of immunity to an infectious agent.

Possible ELISA results

What is ELISA analysis
What is ELISA analysis

Depending on the content of the analysis, the form may present data in the form of a table listing all antibodies or antigens with notes on a negative or positive reaction, or the quantitative value of the result (negative, weakly positive, positive or sharply positive) will be indicated. The latter option determines how many antibodies are contained in the analyzed sample. Another quantitative indicator is the antibody avidity index, expressed as a percentage.

It indicates how much time has passed since the beginning of the infectious process (the higher the index, the more).

Today, thousands of types of ELISA test systems are produced, allowing the detection of specific antibodies and antigens in a wide variety of pathologies.

Therefore, this analysis is used in almost all medical industries. The diagnosis made with the help of ELISA is a guarantee of the appointment of adequate therapy and effective treatment of the disease.

Finally

Sometimes, having detected IgG antibodies in the test results, for example, toxoplasmosis or herpes, patients panic, not seeing that IgM antibodies that indicate the presence of a current infection may not be present at all. In this case, the analysis speaks of a previous infection, to which immunity has developed.

In any case, it is better to entrust the interpretation of the analysis results to the doctor, and with him, if necessary, determine the treatment tactics.

Find out more:

  • Analysis for a disgroup: what is it, preparation and conduct
  • Analysis of feces for dysentery: how to take, terms and methods
  • Analysis for toxoplasmosis: why and how to take it right

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