Table of contents:
- What is an ELISA blood test
- What are immunoglobulins
- How is blood ELISA performed?
- Immunoassay for parasites by ELISA
- How is the ELISA method used?
- Immunological analysis of blood by ELISA
- Scope of immunological blood test by ELISA
- Indications for appointment and detected diseases by ELISA method
- Benefits of the ELISA method
- Disadvantages of the ELISA method
- Possible ELISA results
Video: ELISA - Enzyme-linked Immunosorbent Assay: Transcript
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.
The content of the article:
- 1 What is an ELISA blood test
- 2 What are immunoglobulins
- 3 How blood ELISA is performed
- 4 Immunoassay against parasites by ELISA
- 5 How the ELISA is used
- 6 Tests for immunological blood analysis by ELISA
- 7 Scope of immunological analysis of blood by ELISA
- 8 Indications for use and detected diseases by ELISA
- 9 Advantages of the ELISA method
- 10 Disadvantages of the ELISA method
- 11 Possible ELISA results
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. This study allows 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 (pathogenic agents). Among antibodies, immunoglobulins, which can exist in the form of immunocomplexes, are of paramount importance.
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.
Due to the low price and use of blood as a biomaterial, the method is used as a screening method. For example, if parasitosis is suspected, patients donate blood to determine antibodies to roundworms, lamblia, etc. If the result is positive, then you should not immediately start treating parasites - it is necessary to compare the clinical picture, the results of ELISA and, possibly, the results of other examination methods.
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 long since died, but their light has been shining until now, for centuries. In fact, we only see a star trail. There is light, but the star has long been gone.
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 immunoglobulins
5 main classes of immunoglobulins have been discovered and studied - 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 2 weeks 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 detected 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.
The 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 carrying out two or three tests made with an interval of 2 weeks.
Immunoglobulin E (IgE) is used in the practice of parasitology. Immunoglobulin D (IgD) is located on B-lymphocytes and is found in low concentrations in healthy people. After 10 years of life, it reaches its maximum values. The amount of immunoglobulin D increases during pregnancy, in patients with systemic connective tissue diseases, bronchial asthma, and diseases caused by an immunodeficiency state.
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 taking 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 a complete recovery after a considerable amount of time.
If IgA and IgM are not detected, and IgG manifests itself positively, then most likely 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.
For a chronic infection in the phase of subsiding of the process (remission), ELISA shows negative values of immunoglobulin M (IgM), while the result of immunoglobulins G (IgG) and A (IgA) will be positive.
Immunoassay for parasites by ELISA
ELISA is an abbreviation for enzyme-linked immunosorbent assay for parasites. It implies medical testing of a person's immune system. The test is based on the ability of antibodies to change their color. This diagnostic method has many positive features. For example, he is able to detect a huge variety of diseases caused by infection. It is most effective in cases of diseases caused by parasitic organisms.
What the presented technology gives: determination of the presence of helminths in blood; looking for other pathogens in the body; you can find out the reasons for the deterioration of your health; the treatment is also based on analyzes obtained in this way; you can monitor the health of 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 presumptive 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?
It would be a big mistake to confuse the ELISA method with the method of probing and subsequent study of feces. The latter are carried out using methods at the microscopic level, when a stool sample given by a patient is taken, or it is taken from a potential patient directly in a medical institution. In the sample, they try to detect helminthic invasions and other components, one way or another associated with the vital activity of parasites. Not only microscopic parasitic organisms are studied, but also their remains, their eggs and larvae.
Interpreting ELISA may not give you a complete understanding of the problem, so it is best to consult a doctor or laboratory assistant. It is also a mistake to believe that this method is relevant only if helminths parasitize in the intestine. Many other organs are also diagnosed - parasites can live in the duodenum, biliary tract, liver and even in the pancreas.
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.
The relevance and plausibility of the test results are directly proportional to the qualifications of medical personnel, the technical equipment of the laboratory, as well as the absence of any negligence or inattention among doctors. However, even the most attentive and responsible laboratory assistant will experience enormous difficulties if the parasite is present in the body in its minimal population, or if the clutch was performed immediately at the time of testing.
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.
Basically, for the ELISA analysis, the biological material under study is blood, however, cerebrospinal fluid, the contents of the vitreous body, amniotic fluid, etc. can be examined.
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 the 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 pathogens 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, as they are present there in large quantities.
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;
- CC3 for 4 weeks, a blood test for immunoglobulin is determined by all three types;
- during 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 can be present or absent.
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 (diagnostics 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. 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 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. It is impossible to cover the full list of indications for ELISA.
The most common goals of analysis are:
- diagnostics 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).
Benefits of the ELISA method
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, in order to identify the 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, 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 ELISA method
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.
Possible ELISA results
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.
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.
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).
Find out more:
- Antibody blood test: diagnosing the immune system
- Immunoassay blood test in parasitology
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