- modern laboratory research, during which a search for specific antibodies in the blood or antigens to specific diseases is carried out in order to identify not only the etiology, but also the stage of the disease. ELISA results can be provided qualitatively and quantitatively.
ELISA is currently used in the following situations:
1) Search for specific antibodies to any infectious disease;
2) search for antigens of any diseases (infectious, venereal);
3) study of the patient's hormonal status;
4) examination for tumor markers;
5) examination for the presence of autoimmune diseases.
The advantages of the ELISA method:
1) High specificity and sensitivity of the ELISA method (over 90%).
2) Possibility of determining the disease and tracking the dynamics of the process, that is, comparing the amount of antibodies at different time intervals.
3) Availability of ELISA diagnostics in any medical institution.
Relative disadvantage:
1) Identification of the immune response (antibodies), but not the pathogen itself.
Basic concepts
Before clarifying the essence of the ELISA method, let's briefly understand some of the concepts.
Antibodies (or immunoglobulins - Ig)
- specific proteins produced by B -
lymphocytes (immune cells) in response to any infectious pathogen (viruses, bacteria, fungi, etc.) entering the body. There are immunoglobulins A (IgA), immunoglobulins E (IgE), immunoglobulins M (IgM), immunoglobulins G (IgG), immunoglobulins D (IgD). They differ from each other in molecular shape and weight, half-life, participation / non-participation in infectious processes, timing of detection from the moment of infection. If we consider the molecular weight, then most of all it is in IgM - it is a pentamer (950,000 daltons), unlike other Ig (from 150 to 200,000 Da), due to which IgM simply cannot pass through the placental barrier. Therefore, the detection of IgM in a child of 1 year of age is always a sign of an infection in the fetus. In the blood serum, the bulk of immunoglobulins is represented by IgG (75-85%), and the lowest is IgE (0.003%). Only IgA, M, G are directly involved in the infectious process. IgE are a sign of allergic reactions and diseases, and IgD can be found only in the tissue of the lymph nodes and tonsils, plays a role in the formation of local immunity.
Antigens - high molecular weight substances of organic origin, in particular pathogens of infectious and other diseases, as well as substances of various altered cells formed in a particular disease (autoimmune diseases, oncology).
Immune complex - an antigen-antibody complex involved in the immune process.
What is the ELISA method based on?
There are several types of ELISA (direct, indirect, blocking method, competitive), however, in practice, heterogeneous solid-phase immunosorbent assay or ELISA (enzyme linked immunosorbent assay) is most often used
The basis of the enzyme-linked immunosorbent assay is the immune response of antigen and antibody with the formation of an immune complex: antigen-antibody, as a result of which there is a change in the enzymatic activity of specific labels on the surface of antibodies.
In simple terms, this process can be divided into several stages:
1) On the surface of the wells of the tablet of the doctor conducting the examination, there is a purified antigen of a certain pathogen. When biological material (blood serum) is added to the patient, a specific reaction occurs between this antigen and the desired antibody (immunoglobulin). This compound will act as a "special antigen" in the next step.
2) At this stage, the formation of IC (immune complexes) is taking place - a reaction between a "special antigen" and a conjugate (this is an immunoglobulin labeled with the enzyme peroxidase). A special chromogen is added. The result of such an enzymatic reaction is the formation of a colored substance in the well of the plate, the color intensity of which depends on the amount of immunoglobulins (antibodies) contained in the patient's material.
3) Next, the result is assessed: photometry using a multichannel spectrophotometer, comparing the optical density of the test material with the optical density of control samples, mathematical processing of the results. The amount of antibodies in a patient directly depends on the height of the optical density of a given well.
Typically, 96 well plates are used in practice.
When measuring the optical density (OD) of the test liquid, the amount (or concentration) of antibodies in a certain unit of volume is calculated. The result is then compared to a control sample.
Remember:for each test system, individual indicators are developed to record the results, indicators of norm and pathology (that is, "reference values"). This should be taken into account when evaluating the results of each specific study. It is inappropriate to interpret the results of one laboratory by the "reference values" of another laboratory. It is also incorrect to compare the results of different laboratories with each other.
When setting up ELISA reactions, such a concept as the avidity of antibodies is also important.
Antibody avidity
- this is the strength of the binding of the antibody to the antigen and the amount of antigen associated with immunoglobulins (antibodies). Avidity is of great importance in assessing the estimated duration of infection, which is extremely important in the diagnosis of primary infection in pregnant women.
The basis of the antibody avidity test consists of treating the immune complex (antigen-antibody) with a urea solution in order to destroy the protein. Highly avid bonds remain intact, while low-avid bonds are destroyed. The result is displayed as an avidity index, expressed as a percentage (%).
What diseases are detected using ELISA diagnostics?
2. Markers of autoimmune diseases and indicators of human immunity(total IgE, total IgG, total IgA, total IgM, total IgD, secretory IgA, IgG 2, IgG4, CEC-circulating immune complexes, IgA and IgG to gliadin and others)
3. Cancer markers(TNF - tumor necrosis factor, CEA - cancer-embryonic antigen, PSA - prostate-specific antigen, HCG - chorionic gonadotropin, CA 125, alveomucin and many others)
4. Reproductive disorders I (estradiol, progesterone, prolactin, testosterone, AFP-alpha-fetoprotein, FSH-follicle-stimulating hormone and others)
5. Diseases of the thyroid gland(free and bound T3, T4, thyroglobulin, thyroperoxidase - TPO, thyroid stimulating hormone - TSH).
This list is not presented by all diseases that are diagnosed using enzyme-linked immunosorbent assay.
Material for ELISA analysis and rules for its collection
The most common material for the ELISA reaction is the patient's blood serum taken on an empty stomach. The material can also serve as cerebrospinal fluid, amniotic fluid, the contents of the vitreous humor, mucus of the cervical canal and urethra, smears.
Preparing patients for the delivery of material for ELISA
ELISA manufacturing time
Immunoassay of the material is carried out quickly, within a day. Delays can be in different laboratories due to the accumulation of a certain amount of sera.
Possible results of ELISA diagnostics
When evaluating the results for specific infections, the class of antibodies detected and their amount are important. This determines not only the question of the etiology of the infection (whether it is there or not), 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 timing of the appearance of antibodies (immunoglobulins - Ig)?
The earliest antibodies are IgM... They can be detected in 1-3 weeks after a possible infection, which characterizes the acute phase of the infectious process. The second situation of the appearance of IgM antibodies is the activation (or exacerbation) of a chronic process. IgM antibodies circulate on average for about 3 months, then their number gradually disappears. However, in some patients, trace amounts of IgM can be detected within 1–2 years of infection.
Modern test systems are highly sensitive, as a result of which nonspecific false-positive results are encountered (often in pregnant women). Therefore, in this group of patients, positive IgM must be rechecked!
IgA antibodies appear 2-4 weeks after infection, but in an amount sufficient for detection - after a month. Serum IgA is synthesized by the plasma cells of the spleen, lymph nodes and mucous membranes. Secretory IgA concentrate on the mucous membranes to fulfill their protective function - they participate in local immunity.
From the 4th week after infection, IgG antibodies begin to appear. In 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 (mycoplasmosis, chlamydia, trichomoniasis), the IgG level is not high, it decreases significantly due to the lack of immunity in these infections.
Detection options for antibodies of different classes:
Isolated detection of IgM antibodies suggests primary
infection.
- Simultaneous detection of IgM and IgG in the blood is characteristic of primary infection
in the previous 2-3 months, as well as with exacerbation of a chronic disease. Therefore, during pregnancy, the presence of IgM is not always a sign of primary infection.
- Detection of IgG in isolation may indicate immunity to this disease,
and chronic infection. In the second situation, both the amount of antibodies (titer) and the change in this titer over time are important. Usually, studies are carried out at intervals of 2-4-6 weeks.
- Detection of IgA isolated or with IgM indicates primary infection. At
the appearance of IgA together with IgG is expected to activate a chronic infection (on average, 2 weeks from the moment of exacerbation).
Definition IgG antibody avidity is an excellent complementary stage in the diagnosis of primary infection from long-standing infection, which has its clinical significance, first of all, in assessing the risk of intrauterine infection of the fetus. Detection of low-avidity IgG indicates a primary infection and is detected on average 4-6 months after infection, less often longer. Low avian IgGs require other laboratory confirmation of primary infection (IgM). Highly avid antibodies are either a sign of a chronic disease and its exacerbation, or formed immunity.
Features in infants:in children under one year old, and sometimes even 1.5 years old, maternal IgG to various infections circulate in the blood (that is, they penetrate through the placenta from the mother to the fetus during intrauterine development). They are not in themselves a sign of present infection. If IgM is detected at this age (recall that maternal IgM cannot penetrate the placenta), then this is a sign of intrauterine infection or an infection acquired after birth.
Quantitative ELISA method
The result of ELISA diagnostics (using an enzyme immunoassay analyzer) is displayed in certain units of measurement:
- Optical density (OD) of the sample - the concentration of specific antibodies per unit volume. The higher the OD of the sample, the higher the concentration of antibodies. Some results refer to the positivity coefficient (KP), which is also the optical density of the sample.
- Units of antibody concentration (nanogram / milliliter or ng / ml).
- In the form of serum titers: 1:20, 1:40, 1: 100, 1: 200, 1: 400, 1: 800, 1: 1200 and so on. Diagnostic titers (in which the diagnosis is made of the disease, and not the fact of infection) are different for different diseases.
- In the form of symbols - "+", "-", "?" (+, ++, +++, ++++).
- In the form of a qualitative assessment according to a given criterion (positively or negatively).
It is only a doctor who can correctly estimate the amount of antibodies, a variant of the class detection of immunoglobulins, and, therefore, set the stage of the disease and the need for treatment.
We must not forget that for any test system, its own "reference values" (variants of the norm) are developed, if exceeded, this or that disease is diagnosed (variants of pathology). For different test systems, "reference values" are different.
Correct comparison of ELISA results taken in dynamics is possible only if they are produced in the same laboratory.
Infectious disease doctor N.I. Bykova
The diagnostic method (ELISA) is informative and not too expensive, therefore many laboratories offer their clients this method (enzyme-linked immunosorbent assay). The study is carried out on an empty stomach, blood for analysis is taken from the patient's cubital vein. It is advisable not to smoke or drink alcohol before ELISA.
What is an ELISA blood test
Among the methods of blood analysis, which allow assessing the body's ability to resist infectious diseases and showing the phase of the disease, enzyme-linked immunosorbent assay (ELISA) occupies an important place. Carrying out this study allows you to comprehensively assess the activity of the protective function of the blood and identify the state of immunodeficiency in infectious pathologies, as well as blood diseases, autoimmune processes, hormonal problems.
This is a laboratory study that allows you to determine the presence of specific antibodies (protective factors of the blood of a protein nature) to certain antigens (disease-causing agents). Among antibodies, immunoglobulins are of paramount importance, which can exist in the form of immunocomplexes.
Immunoglobulins are produced as a result of complex neurohumoral reactions of human immunity, arising as a response to the introduction of foreign antigens. For each type of pathogenic agent, its own specific antibodies are produced. They act by "binding" an antigen or a pathological microorganism, forming a complex compound "antigen-antibody" with subsequent neutralization, enzymatic lysis, phagocytosis reactions and withdrawal from the body. It is by the presence of certain complexes that the ELISA method determines the type of pathogen or a harmful substance present in the patient.
It is worth remembering that after the completed course of treatment, antibodies can remain in our body for a very long time, even after the infection has left our body, i.e. the so-called "serological scar" remains. For example, there are thousands of stars in the night sky. Many of these stars have died long ago, but their light has been going down to us for centuries. In fact, we only see the trail of a star. There is light, but the star has been gone for a long time.
But if there is no light, this does not mean that the star was not there. It's the same with antibodies. Their presence does not guarantee the presence of the desired infectious agent in the body. The absence of antibodies does not mean that there is no infection. If the result of the analysis by ELISA is positive, then this means that you need to look for an infection with more specific and expensive methods - PCR, bacteriological cultures. A false positive result is possible if several microbes have a similar antigenic structure, then “similar” antibodies will be produced to different microbes.
What are the immunoglobulins
Openly and studied 5 main classes of immunoglobulins - IgA, IgM, IgG, IgD, IgE. the role of the rest has not yet been fully elucidated and it is at the stage of scientific research.
The main task of immunoglobulin A (IgA) is the protective functions of the mucous membranes of the respiratory tract, gastrointestinal tract and urinary system. With an acute onset of the disease, it is impossible to identify them. These protective complexes appear only from the 2nd week of the onset of the disease, sometimes later. The bulk of immunoglobulin A is concentrated in mucous tissues. Approximately 80%. The rest of the antibodies circulate in the blood.
The main function is to neutralize and destroy microorganisms. After the acute manifestations of the disease have subsided, the amount of these immunoglobulins begins to decrease and completely disappears for up to 8 weeks after the onset of the disease. If IgA is found at a later date, then this indicates the chronization of the process.
The main and first markers of the acute phase of the developing pathology are class M immunoglobulins (IgM). They are found by the 5th day of the onset of the malaise. Their presence in the blood can be determined for about 6 weeks. Then they start to disappear quickly.
Residual immune response is characterized by the presence of class G immunoglobulins (IgG) in the blood. The appearance of these factors in the blood is detected about a month after the onset of the disease. In the future, they can be determined for many months, years and even all life, performing a protective function against the return (relapse) of the disease, and in some cases making it impossible for the secondary development of pathology.
If the amount of immunoglobulin G begins to rise again, then re-infection can be suspected. A similar conclusion can be made by conducting two or three tests, made with an interval of 2 weeks.
How is blood ELISA performed?
For enzyme immunoassay, in most cases, the blood of patients is used, sometimes the vitreous tissue, fluid of the spinal canal, and amniotic fluid are taken.
Blood is drawn through an injection needle into a syringe from the cubital vein. The study is carried out on an empty stomach. It should be remembered that certain medications may affect the test result. Before donating blood, you must refrain from smoking, drinking alcohol. Intake of narcotic substances can distort the results.
In the case of negative values of immunoglobulins IgM, IgG, IgA, we can talk about the absence of the disease or its initial phase, and the result with minuses is possible with full recovery after a significant amount of time.
If IgA and IgM are not detected, and IgG manifests itself positively, then in all likelihood we are talking about the formed immunity after an infectious disease, or after vaccination.
If IgA and IgM are not detected, and IgG manifests itself positively, then in all likelihood we are talking about the formed immunity after an infectious disease, or after vaccination
In the case of a high titer of IgM with negative values of IgG, IgA, it can be concluded that there is an acute infectious disease.
Simultaneous positive values of the results of immunoglobulins - IgA, IgM, IgG are characteristic of the acute phase of recurrence of the existing chronic disease.
What the presented technology gives: determination of the presence of helminths in the blood; looking for other pathogens in the body; you can find out the reasons for the deterioration of your health; treatment is also based on analyzes obtained in this way; you can monitor your immune system.
Another good feature is the ability to track cancer markers, regardless of their origin, but subject to their presence in the body, of course. This test is also suitable for describing the state of the human reproductive system. The presence of certain proteins, hormones and peptides makes it possible to judge the partner's potential in terms of conceiving a child, as well as the estimated quality of the future fetus.
A blood test for Giardia is a fairly popular practice among modern doctors. In addition, this research method is an excellent tool for biomedical analytics and quantitative statistics in terms of specific antigens.
How is the ELISA method used?
True, these are more complex cases, so the quality of such an analysis will greatly depend on the workers of the laboratory performing the testing. Features of the technology and its difference from old laboratory research:
- now, instead of a stool sample, blood is used to determine the presence of helminths;
- the study of the sample is carried out in the laboratory very quickly, the next day you can get complete information;
- the cost of laboratory research is inexpensive, since theology is very simple;
- a blood test for helminths gives high accuracy rates.
Immunological analysis of blood by ELISA
Few people know about what blood tests are from the point of view of the human immunological system, since these tests are not so common. As a rule, such a blood test provides information about the immunodeficiency virus in the human body and is anonymous, since it is carried out at the request of the patient.
For sampling, blood taken from a vein on an empty stomach is used, from which serum is obtained for research by centrifugation. In addition, the study of blood serum can reveal a number of sexually transmitted diseases (syphilis, herpes, chlamydia), as well as all types of hepatitis, measles, rubella, mumps and toxoplasmosis.
Basically, for ELISA analysis, the biological material under study is blood, however, cerebrospinal fluid, the contents of the vitreous body, amniotic fluid, etc. can be examined.
Immunoglobulins are immune molecules that can bind to and neutralize most infectious agents and toxins in the body. In this case, the most important characteristic of immunoglobulins is their specificity, that is, the ability to bind to a specific antigen. It is this property that is used to conduct a blood test for immunoglobulin.
There are five types of immunoglobulins, but the most studied are immunoglobulins A, M, and G. Immunoglobulins M and G are active in the blood. Immunoglobulins A are a kind of barrier on the surface of the mucous membranes, since they are present there in large quantities.
An immunological blood test allows you to determine the type of immunoglobulins, thanks to this, ELISA allows not only diagnosing the disease, but also determining the stage of this and tracking the dynamics of the disease:
- in the first 2 weeks of the disease, only immunoglobulins A are found;
- from the 2nd to the 3rd week of the disease, immunoglobulins A and M are found in the blood;
- Сс3 for 4 weeks, a blood test for immunoglobulin is determined by all three types;
- with recovery, immunoglobulins M disappear in the blood, and the amount of A and G decreases 2 to 4 times;
- in the presence of a chronic process, immunoglobulins G are necessarily present in the blood, immunoglobulins M are absent, immunoglobulins A may or may not be present.
Scope of immunological blood test by ELISA
- Diagnostics of viral diseases: hepatitis, herpes, Epstein-Barr virus, cytomegalovirus, etc.
- sexually transmitted infections: chlamydia, gonorrhea, Trichomonas, mycoplasma, ureaplasma;
- syphilis; endocrinology (determination of hormone levels);
- tumor markers (diagnostics of oncological diseases); immunology (diagnosis of immunodeficiency);
- allergology (diagnosis and treatment of allergies).
Serological blood test is a laboratory blood test method that is used to diagnose infectious diseases and determine the stage of the infectious process. The serological response is based on the interaction of antibodies and antigens.
Determination of antigens is used to determine the genus and species of microorganisms. This research method is used in urology and venereology. Blood for a serological blood test is taken in the morning on an empty stomach from a vein.
Indications for appointment and detected diseases by ELISA method
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 formed 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. It is impossible to cover the full list of indications for ELISA.
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.
ELISA has largely replaced the "gold standard" of microbiology - a bacteriological diagnostic method, during which, to identify a pathogen, it was required to isolate it from the body, and then grow the culture on a nutrient medium in a test tube for several days.
All the time, while the analysis was being carried out, doctors were forced to treat the patient "blindly", guessing about the origin of the microorganism by the symptoms of the disease. The determination of IgM using ELISA allows an accurate diagnosis to be made already in the first days of the disease.
The high degree of manufacturability of the enzyme immunoassay minimizes the influence of the human factor, which reduces the likelihood of error. Most of the ELISA test systems and reagents used in modern laboratories are produced in an industrial environment, which guarantees an accurate result.
Disadvantages of the ELISA method
Unfortunately, to carry out ELISA, you need to know what exactly to look for: the analysis method 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 the diagnosis of infectious diseases, the 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.
Possible ELISA results
Depending on the content of the analysis, the form may contain data in the form of a table listing all antibodies or antigens marked with 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.
If you have the necessary reagents and good organization of the laboratory, you will receive the test result within 1–2 days after blood sampling. In some cases, if an emergency response is required, this period can be reduced to 2-3 hours.
Being a modern type of laboratory research, ELISA, or enzyme-linked immunosorbent assay, allows you to find specific antibodies or antigens to certain diseases in the blood. This allows you to detect both the etiology of the disease and determine its stage. Moreover, the results of this type of research can be issued both quantitatively and qualitatively. So, let's take a closer look at the principle of the enzyme immunoassay method, its methodology and essence.
What is enzyme immunoassay
Appointed for the most complete comprehensive assessment of health status, enzyme immunoassay allows you to assess the overall health and assess its protective functions. This laboratory study allows you to diagnose infectious, autoimmune, hematological pathologies by analyzing blood.
The essence of the enzyme immunoassay is discussed in the video below:
Who is it assigned to?
This study can be assigned to those patients who have the following diseases:
- diseases of viral origin, which include hepatitis;
- sexually transmitted diseases - chlamydia, Trichomonas, syphilis, ureaplasma, mycoplasma;
- immunodeficiency;
- conducting a preoperative comprehensive examination.
ELISA blood test is also prescribed to determine the level of hormones and assess the quality of the type of therapy.
The doctor may prescribe this analysis to establish the stage of the existing disease, which allows timely adjustments to the treatment used. And the high accuracy of the data obtained allows you to have the most detailed picture of health. At the same time, the data obtained after the study is carried out in a very short period of time, which makes it possible to track the dynamics of the development of the pathological process.
Why take such tests
Since, thanks to the ELISA blood test, it is possible to obtain a significant amount of information about the state of health and pathological processes occurring in the body, it is he who makes it possible to take into account the initial data (general health, stage of the disease, dynamics of the development of the pathological process, the indicator of the effectiveness of the therapy used) when compiling treatment regimens.
For this reason, to obtain the most pronounced result of treatment and the fastest termination of the pathological process in the body, an ELISA blood test is prescribed. Based on the data obtained, serious diseases of the immune system, the presence of antigens in the blood and the causes of allergies can be cured more quickly using the most effective methods.
The prescription of an ELISA analysis is carried out for a variety of pathologies, and it should be done only as directed by a doctor. The frequency of the analysis is also set by the doctor, and when donating blood for the ELISA analysis, the picture of the disease is the most complete. Since obtaining the dynamics of the course of the disease is possible with the delivery of this test more than once, most often blood donation can be prescribed from three to five times. This makes it possible to compare the amount of antibodies in the blood at different time intervals.
Types of such a procedure
There are several types of enzyme immunoassay. They differ in the type of fluid taken from the human body, on the basis of which its composition and the presence of certain antigens are studied.
At the same time, not only human blood can be taken for analysis, but also his other fluids:
- amniotic fluid
- cerebrospinal fluid
- the contents of the vitreous body,
- strokes,
- mucus from the urethra and cervical canal.
Carrying out the operation itself for taking a certain type of fluid is standard and is carried out in a day hospital.
Indications for
Usually, an ELISA analysis is prescribed by a doctor if it is necessary to obtain a detailed picture of the current disease, which takes place in any form: chronic, sluggish or acute. And the indications for this type of analysis can be considered the following conditions and therapeutic goals:
- search for antigens of certain diseases;
- determination of hormonal status;
- detection of the hepatitis virus in the body;
- research on;
- search for antibodies to any type of infectious disease;
- examination for the presence of autoimmune damage to the body.
For an enzyme-linked immunosorbent assay, see the video below:
Contraindications for
To date, no contraindications for enzyme immunoassay have been identified.
During pregnancy, when there is a constant change in the content of hormones in the blood, it is necessary to carry out this analysis several times to confirm the result. Newborns and infants may also have incorrect test data: during intrauterine development, certain types of antibodies can enter the fetal blood through the mother's placenta. Therefore, their presence in the analysis taken should not be considered a sign of an existing infection.
Analysis safety
Carrying out the procedure for taking any kind of liquid from the human body does not bring any negative effect on the body. Complete sterility during manipulation avoids the likelihood of contracting any kind of disease.
Preparation for conducting
To obtain the most reliable results of the study, one should refrain from drinking alcoholic beverages and narcotic drugs before taking blood (or other liquid) for analysis.
How is the procedure going, sensations during it
For ELISA analysis, the patient's blood is taken strictly on an empty stomach: you should not eat any kind of food at least hours before the procedure. The analysis is taken from the cubital vein.
The doctor is informed about the presence of any diseases and medications taken in advance, most often the drugs will be canceled at the time of blood donation. The sensations during the procedure are similar to taking blood for a biochemical analysis.
Decoding the results
ELISA diagnostics allows you to determine the presence of infection in the body, the activity of the pathological process and the etiology of the existing infection. The quick receipt of the result of the analysis (within 24 hours) is one of the advantages of this type of research.
The process of decrypting the information received is carried out by the doctor. It should be borne in mind that the correctness of the results obtained on the dynamics of any processes is guaranteed when passing analyzes in one laboratory.
Average cost of the procedure
The average cost of an ELISA study depends on the direction of the analysis and the determination of specific values. Thus, the determination of serological markers of various types of infectious diseases (anti-HAV IgG, anti-HAV IgM, HBsAg) will cost from 200 to 320 rubles and is carried out within 2 working days. The indicator of the cost of this procedure is also considered its advantage: the availability of prices for any type of research allows conducting research at any size of the budget.
The cost of an ELISA study depends on the policy of the medical institution, but it should be considered a publicly available procedure that allows you to get a detailed picture of the existing disease and provide the most complete treatment.
For the norms and features of the ELISA study, see the video below:
(ELISA) is a method for examining blood in a laboratory, based on the search for special cells - antibodies to various diseases. The method allows not only to identify the pathogen, but also to establish 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:
- The ability to search for all existing antibodies to infectious diseases in the patient's blood.
- High availability of the research method. Today, ELISA analyzes can be performed by any medium-sized laboratory.
- Almost 100% specificity and sensitivity of the method.
- The ability to search for antibodies and antigens, as well as to establish the stage of the pathological process and track its dynamics, thanks to the comparison of the quantity.
Such a number of advantages over other analyzes completely overshadows one single drawback of the analysis: it is able to detect antibodies, but not the pathogen itself.
Key Terms for Assessing Analysis
In order to understand what an ELISA analysis is, what it is and how it is performed, you need to get acquainted with the basic terms used by specialists.
- Antibody- a protein that is produced by the cells of the human immune system (type B lymphocytes). They respond with a specific reaction to the ingress 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 weight, response rate, 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 are involved in allergic reactions.
- Antigen- a foreign agent of organic origin and high molecular weight. Most often it is pathogens or their biologically active substances.
- An antigen-antibody complex, or an immune complex, is a direct combination of a foreign substance and an immunoglobulin, which gives rise to an immune response.
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? The method can be easily described by briefly describing its stages.
Preparatory stage... The laboratory doctor uses a special plate with 96 wells. An antigen of a specific pathogen is applied to the surface of each well.
Stage 1. A blood sample is taken, which is then applied drop by drop to the well. In the hole, a reaction is triggered between the antigen and the antibody in the blood.
Stage 2. In the hole, a reaction is in full swing with the formation of immune complexes. 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, a special device called a "spectrophotometer" is used. It compares the density of the material in the well and the control sample. Then the device generates the result by means of mathematical analysis.
Evaluation of results and purpose of ELISA
The interpretation of the result depends on several important nuances:
- The optical density of the well.
- Well plate manufacturer (test systems).
- The laboratory in which the study was carried out.
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 avidity of antibodies. This parameter characterizes the amount of antigen, 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 break down the weak bonds between the antigen and the antibody and leave only strong ones. The value of an avidity test is that it can be used to find out the time of infection. This information is extremely important for the diagnosis of pregnant women.
An ELISA blood test is used for:
- To search for various pathogen antigens.
- For the study of hormonal levels.
- For examination for the presence of autoimmune pathology.
- To detect markers of cancer.
Varieties of ELISA
ELISA analysis has the following varieties:
- Indirect.
- Straight.
- Competitive.
- 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 a complex of an antigen with an antibody with a color change on the surface of the well.
The quantitative ELISA blood test deserves special attention. It is not a form of analysis, but a way of evaluating results. Thanks to him, the number of antibodies is counted 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, and also on the laboratory.
Diseases detected by ELISA
ELISA is a blood test that can detect a huge number of various infectious diseases. Moreover, both viral and bacterial diseases are detected with the same accuracy. For example, with the help of the formation of immune complexes, it is possible to prove the presence of antigens of the causative agents of the following diseases:
In addition, ELISA allows you to detect:
- Cancer markers - TNF (tumor necrosis factor), PSA (prostate-specific antigen), CEA (cancer-embryonic antigen), CA-125 (ovarian tumor marker)
- The pregnancy hormone is hCG (human chorionic gonadotropin).
- Reproductive system disorders: hormones of the female and male reproductive systems.
- Thyroid pathology.
It is important to mention that the ELISA test for HIV today is the main way to diagnose this dangerous disease.
ELISA material and sampling technique
To perform ELISA, the patient takes blood on an empty stomach. Further, serum is obtained from the blood, which is directly used for analysis. In addition, ELISA can be performed on cerebrospinal fluid (cerebrospinal fluid), mucus of the cervical canal (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 sampling.
Terms of receipt and interpretation of results
The timing of receiving a response from the laboratory depends not on the speed of its work, but on the stage of the disease and which 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 the chronic one 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 2-3 weeks later, either alone, or together with M, indicating an acute infection, or together with G, indicating a chronic process.
Such different times for the appearance of antibodies in the blood will make the patient wait a long time for the result. Waiting more than a month after the ELISA test is performed is acceptable. Decoding and interpretation by a doctor also take a certain period of time.
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