Screening test in the diagnosis of HIV infection. Diagnosis of HIV Infection The standard method for diagnosing HIV is

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The following are subject to testing for HIV infection:

2. Persons with suspected or confirmed diagnosis: bacterial infection in children under 13 years of age, multiple and recurrent; candidiasis of the esophagus, trachea, bronchi or lungs; cervical invasive cancer; disseminated or extrapulmonary coccidioidomycosis; extrapulmonary cryptococcosis; cryptosporidiosis with diarrhea for 1 month or more; cytomegalovirus lesions of other organs, except for the liver, spleen, lymph nodes in patients older than 1 month; cytomegalovirus retinitis with loss of vision; herpetic infection that causes multifocal ulcers that do not heal within 1 month, or bronchitis, pneumonia, esophagitis; histoplasmosis disseminated or extrapulmonary; isosporiasis with diarrhea for more than 1 month; tuberculosis widespread or extrapulmonary; pulmonary tuberculosis in adults or adolescents over 13 years of age; extrapulmonary tuberculosis; other disease caused by mycobacteria, except M. tuberculosis disseminated or extrapulmonary; pneumonia caused by pneumocystis; progressive multifocal leukoencephalopathy; salmonella (except Salmonella typhi) septicemia, recurrent; brain toxoilase in children older than 1 month; Kaposi's sarcomas; lymphoid interstitial pneumonia in children under 13 years of age; Burkitt's lymphoma; immunoblastic lymphoma; primary brain lymphoma; wasting syndrome, hepatitis B, carriage of HBsAg; infectious mononucleosis; recurrent herpes zoster in persons over 60 years of age; sexually transmitted diseases.

In a highly specialized laboratory are carried out:

a) determination of antibodies, antigens and immune complexes circulating in the blood; cultivation of the virus, detection of its genomic material and enzymes;

b) assessment of the functions of the cellular link immune system. The main role belongs to the methods of serological diagnostics aimed at the determination of antibodies, as well as pathogen antigens in the blood and other biological fluids of the body.

Testing for antibodies to HIV is carried out in order to:

a) safety of blood transfusions and transplantations;

b) surveillance, testing to monitor the prevalence of HIV infection and study the dynamics of its prevalence in a particular population;

c) diagnosis of HIV infection, i.e. voluntary testing of blood serum of practically healthy people or patients with various clinical signs and symptoms similar to HIV infection or AIDS.

The system for laboratory diagnosis of HIV infection is based on a three-stage principle. The first stage is screening, designed to perform primary blood tests for the presence of antibodies to HIV proteins. The second stage is referential - it allows using special methodological techniques to clarify (confirm) the primary positive result obtained at the screening stage. The third stage - expert, is intended for the final verification of the presence and specificity of HIV infection markers identified at the previous stages of laboratory diagnostics. The need for several stages of laboratory diagnostics is primarily due to economic considerations.

In practice, several tests are used to identify HIV-infected people with a sufficient degree of certainty:

ELISA (ELISA) test (enzyme-linked immunosorbent assay) for detecting the first level is characterized by high sensitivity, although less specificity than the following;

Immune blot (Western-blot), a very specific and most used test to differentiate between HIV-1 and HIV-2;

Antigenemia p25-test, effective in the initial stages of infection;

Polymerase chain reaction (PCR).

In cases of mass screening of blood samples, it is recommended to test mixtures of sera from a group of subjects, compiled in such a way that the final dilution of each sample does not exceed 1:100. If the serum-current mixture is positive, each serum of the positive mixture is tested. This method does not lead to loss of sensitivity in both ELISA and immunoblot, but reduces labor costs and the cost of the initial examination by 60-80%.

In the primary serodiagnosis of HIV infection, total antibodies are determined using screening screening tests - ELISA and agglutination reactions. At the second (arbitration) stage, a more complex test is used - an immunoblot, which allows not only to confirm or reject the initial conclusion, but also to do this at the level of determining antibodies to individual proteins of the virus.

Linked immunosorbent assay(ELISA) is the main and most widely used method for determining antibodies to HIV. But the disadvantages of using ELISA in the serodiagnosis of HIV infection include frequent false positive results. In this regard, the result in the ELISA is not a basis for concluding that the subject is HIV-seropositive. This is due to insufficient purification of the immunosorbent from ballast proteins; spontaneous binding of serum antibodies to plastic, if its areas not occupied by the immunosorbent are insufficiently blocked or not blocked by a completely special neutral protein; cross-interaction with HIV proteins of the immunosorbent of various proteins present in the blood of individuals with certain, more often autoimmune pathological processes such as multiple sclerosis, SLE, tuberculosis; with frequent donation, infectious and oncological diseases, burns, pregnancy, repeated blood transfusions, transplantation of organs, tissues, as well as persons on hemodialysis; with the presence of rheumatoid factor in the blood, often provoking HIV false-positive reactions; the presence in the blood of the examined people of antibodies to HIV gag proteins and, above all, to the p24 protein (obviously, antibodies are formed to exogenous or endogenous retroviruses that have not yet been identified). Since anti-p24 is synthesized without fail on early stages HIV seroconversion, further immunological monitoring of persons with antibodies to HIV gag proteins is carried out, as well as their removal from donation.

The sensitivity and specificity of enzyme immunoassay is constantly increasing. As a result, the fourth-generation ELISA is not inferior in its diagnostic capabilities to immune blotting and can be used not only at the screening, but also at the confirmatory stage of diagnosing HIV infection [Smolskaya T. T., 1997].

Immunoblotting is the final method of serological diagnostics, allowing to make a final conclusion about the HIV-positivity or negativity of the subject.

There is a clear correlation between the results of the study of sera in immunoblot and ELISA - twice positive in ELISA with different test systems, serum in 97-98% of cases then turn out to be HIV-positive in immunoblot. If the sera were positive in ELISA only in one of the two test systems used, they are positive in the immunoblot only in 4% of cases. In 5% of cases, when conducting confirmatory studies in people with positive data, the ELISA immunoblot can give “indeterminate” results, and among them, in about 20% of cases, antibodies to HIV-1 gag proteins (p55, p25, p18 ). The presence of antibodies only to HIV-1 gag proteins is a reason for additional examination of blood serum for HIV-2 infection.

The evaluation of the results of immunoblotting is carried out strictly in accordance with the instructions attached to the test system. In the absence of guidance on the interpretation of results, the WHO criteria should be used.

Upon receipt of positive test results at the reference stage of laboratory diagnosis of HIV infection and a negative result of the study by the method of immune blotting, a mandatory repeated expert diagnosis is performed 6 months after the first examination.

If the results of immunoblotting 12 months after the study of the first sample remain negative or indeterminate, then in the absence of risk factors, clinical symptoms or other factors associated with HIV infection, the subject is removed from dispensary observation.

Among serological methods, in case of indeterminate results, the immunoblot is used as an expert diagnosis. radioimmunoprecipitation(RIP). It is based on the use of viral proteins labeled with radioactive iodine, and precipitates are detected using beta counters. The disadvantages of the method include the high cost of equipment, the need to equip special rooms for these purposes.

Persons diagnosed with HIV infection are subject to constant dynamic monitoring with mandatory laboratory examination every 6 months.

Polymerase chain reaction (PCR) reveals premultiplied nucleotide sequences specific for the genome of a given pathogen. Isolated multiplication of a gene or its fragment, called amplification, PCR makes it possible to carry out in vitro using the enzyme thermostable DNA polymerase. For 2-3 hours, PCR allows you to get millions of copies of a specific section of the virus. With HIV infection, from cellular RNA, including the RNA of the virus, if it was reproduced in the cell or was integrated into its genome, using reverse transcription and hybridization with labeled oligonucleotide "probes", a sufficient amount of proviral DNA is obtained for analysis, which is detected and characterized quantitatively , as well as in relation to belonging to the HIV genome, establishing the homology of DNA and virus-specific amino acid sequences by a radioactive or other label of the probe. The sensitivity of PCR is the detection of viral genes in one of five thousand cells.

PCR, including quantitative, can only be used to determine the viral load on plasma to resolve the issue of initiation drug treatment patient or changing antiretroviral medicines. PCR cannot be recommended for diagnosing HIV infection, since even the most cutting-edge methods of its formulation and reagents make it possible to determine the viral load not lower than a certain level - 50 copies / ml. And the complexity of setting up PCR and its high cost (about $ 200) negate its large-scale use as a method of everyday laboratory diagnosis of HIV infection. Thus, PCR remains indispensable only for assessing plasma viral load in patients with already established diagnosis HIV infection in order to address the issue of therapy of patients.

Schematically, the stages of laboratory diagnosis of HIV infection are shown in Fig. one.

Rice. 1. Stages of laboratory diagnosis of HIV infection

During HIV infection, there is a period of "dark laboratory window" when the amount of anti-HIV antibodies is insufficient for the sensitivity of the test systems. This period ranges from one week to three months from the moment of HIV infection, depending on the level of sensitivity of the test system. Given this phenomenon, difficulties arise when examining donated blood from persons who are in the mentioned period of HIV infection. Therefore, in most countries of the world, a system has been introduced for using blood only after it has been stored for 3-6 months in order to carry out a mandatory re-examination for HIV infection of donors of these doses of blood and its components.

The stage of primary manifestations is characterized by the activity of the replicative process. The resulting viremia and antigenemia cause the formation of specific antibodies of the IgM class: anti-p24, anti-gp41, anti-gp120. The p24 antigen in some of the infected can be detected in the blood by ELISA as early as 2 weeks after infection and can be determined up to the 8th week. Next in clinical course HIV infection marks the second rise in the content of the p24 protein in the blood, it falls on the period of the formation of the AIDS stage.

The appearance of complete seroconversion, when a high level of specific antibodies of the IgG class to the structural proteins of HIV gp41, p24, gpl20, is recorded in the peripheral blood, greatly facilitates the diagnosis of HIV infection. Most commercial kits are designed to indicate just such antibodies.

Difficulties in detecting antibodies in HIV-infected patients may arise during periods of massive viremia and antigenemia, when the available specific antibodies in the blood are used up to bind viral particles, and the replicative process is ahead of the production of new antiviral antibodies.

In individuals with an initially weakened immune system, viremia and antigenemia appear earlier and remain at a high level until the outcome of the disease. At the same time, such patients have a low content of free antibodies to HIV, due to two reasons - insufficient production of antibodies by B-lymphocytes and antibody binding of virions and soluble HIV proteins, therefore, to determine infection, test systems with increased sensitivity or modifications of analysis methods are required, providing stage of release of antibodies from immune complexes.

Despite the abundance of specific markers of HIV infection, the most frequently determined is the presence of total antibodies to HIV proteins. The term "total" implies the presence of two classes of antibodies (IgG and IgM) and a wide range of antibodies to various, primarily structural, HIV proteins.

Determination of CD4 cells. The main clinical and laboratory indicator for diagnosing the stage of HIV infection, the degree of destruction of the immune system in patients in everyday life, was the determination of the content of CD4+ lymphocytes: a decrease in the level below 200 cells/mm3 is the main criterion for diagnosing AIDS. It is believed that all HIV-infected individuals with a CD4+ lymphocyte count of 200 cells/mm3 or less require both antiviral therapy and PCP prophylaxis. And although 1/3 of HIV-infected with the number of CO4+-lymphocytes less than 200 cells/mm3 do not have clinical manifestations, experience has shown that they develop symptoms in the next 2 months, so they are all regarded as patients at the stage of AIDS.

Diagnosis of HIV infection at an early stage is essential. The complexity of therapy and the development of pathological complications depend on this. To date, there are many innovative research methods to identify such a terrible diagnosis. This is what will be discussed further.

What methods are available for diagnosing HIV infection?

Laboratory diagnostics

• Antibodies, antigens of pathogens and immune complexes are determined.
• When a virus is detected, it is cultured and genomic material and enzymes are detected.
• The functionality of the immune system is assessed.
• Epidemiological surveillance and monitoring of the prevalence of human immunodeficiency virus is carried out.
• Distribution dynamics are studied and the population is determined.
• It is possible to determine the degree of safety of transplantation and blood transfusion.

Differential Diagnosis

• At the first symptoms of HIV infection, which is in the acute phase, especially if there is a mononucleosis-like syndrome. Diagnosis is based on such pathologies as infectious mononucleosis, syphilis, rubella, adenovirus, leukemia in acute form, yersiniosis, hyperkeratosis.
• If HIV passes into the stage of generalized lymphadenopathy of a persistent nature, then diseases are differentiated in which the lymph nodes increase. For example, lymphocytic leukemia, syphilis, toxoplasmosis, lymphogranulomatosis. In this phase, the patient's symptoms become more pronounced.
• If secondary pathologies are detected, immunodeficiency is differentiated, which has arisen against the background of taking certain groups of drugs - radiation therapy, the use of glucocorticosteroid drugs and cytostatic drugs. Immunity is also significantly reduced in diseases such as myeloma, lymphoid leukemia, oncological neoplasms, and so on.
• If HIV is located in oral cavity, then diseases of the oral mucosa are differentiated.

Express Diagnostics

• The most accurate test is immunochromatographic. The test consists of special strips on which capillary blood, urine or saliva is applied. If antibodies to HIV are detected, then the strip has a color and a control line. If the answer is no, only the line is visible.
• Sets home use OraSure Technologies1. Developer - America. This test has been approved by the FDA.
• There are other rapid tests, but they do not have the approval of specialists, and therefore are undesirable for the test.

If revealed positive reaction for human immunodeficiency virus, it is necessary to additionally conduct an appropriate examination in a clinical setting.

Early diagnosis

In order to independently diagnose the pathology in the early stages, pay attention to the symptoms that exist in this case:

polymerase chain reaction

This is a rather expensive diagnostic, but in some cases it can give a false result. Therefore, when screening for HIV, other methods are additionally used.

immune blotting

The result is determined by the binding of blood proteins to proteins applied to the nitrocellulose strip. If HIV is present in the patient's body, then single lines are translucent. There are certain indicators of identifying lines that signal the presence of HIV. But there are also low numbers. In this case, there is a risk of developing initial stage human immunodeficiency virus, the formation of oncological tumors, tuberculosis, blood transfusion.

ELISA test

There are several types of ELISA tests, but only the latest developments are used - the 3rd and 4th generation. The technique is based on the collection of blood fluid from a vein. There is a certain preparation - the patient should not eat for 8 hours before the test. Therefore, blood is collected on an empty stomach in the morning.

How is diagnosis made during the incubation period?

After that, throughout the year, the person is under the close attention of doctors and undergoes multiple examinations. Only after this period it is possible to accurately establish the diagnosis - HIV.

Features of diagnosis in children

The first tests for HIV in a child are taken on the second day after birth. Then after reaching 2 months, then every 4 months.

To detect pathology in childhood serological examination methods, PCR are used. It is the latter type of diagnosis of the disease that makes it possible to identify the DNA and RNA of the virus in the first months of the baby's life. For this, blood is collected from the baby, which is subsequently placed in a test tube containing the EDTA preservative. Further, the material is stored for 2 days at a temperature not exceeding 8 degrees. But freezing blood is not acceptable. Dry blood fluid, which is obtained from whole blood and dried, can also be used.

Stages of diagnostics

• Pre-sorting, aka screening.
• Reference diagnostics.
• Confirmatory stage or expert diagnostics.

Screening - pre-sorting

You need to know that ELISA can, under certain conditions, give a false positive result. This can be during the period of bearing a child, with autoimmune diseases (psoriasis, rheumatism, lupus, etc.), Epstein-Bar disease and other pathologies.

Reference diagnostics

Confirmation stage - expert

Errors during diagnostics

Paradoxical as it may seem, there is a possibility of obtaining a false positive result. This usually happens during home testing, especially in cases where rapid tests are used. In a clinical setting, this is only possible with certain diseases or conditions:

• period of pregnancy;
• cross-reaction of the body;
• autoimmune pathological disorders;
• colds in the acute stage;
• oncological neoplasms;
• tuberculosis;
• sclerosis.

Feature - if a person is infected with viruses and fungi, then the test result may also be false. This is especially true in allergic conditions.

Preparation for testing

• First of all, you need to visit the appropriate specialist so that he can give you precise instructions on the preparation activities.
• Blood tests are always collected on an empty stomach. Therefore, before going to the clinic, you can not eat anything. Your last meal should be no later than 21:00.
• It is forbidden to smoke on the day of the test.
• Do not drink alcohol the night before.
• If you are taking any medications, be sure to consult your doctor beforehand. Because many drugs are prohibited before taking HIV tests.
• It is not recommended to conduct an ultrasound examination a few days before the collection of the analysis.
• It is not advisable to eat excessively fatty foods and consume a lot of sweets a day or two before the procedure.

Diagnosis of HIV infection (video)

Diagnosis of HIV is one of the primary tasks facing the employees of the dermatovenerological dispensary, as well as the staff of the clinic.

The disease is characterized by doctors as very insidious. It is characterized by a chronic course and is not amenable to full treatment. It is important to detect it in a timely manner in order to take it under control and prevent uncontrolled spread. What are the features of the human immunodeficiency virus, and how they can get infected, patients are often interested.

What are the methods of diagnosing the disease, and what signs make it possible to suspect infection?

Today, from everywhere you can hear about how dangerous HIV infection is. However, few people explain what this danger is. As a result, patients have an incomplete set of information and, as a result, do not take the threat seriously. But HIV is extremely dangerous. It is classified as a slowly progressive viral disease, prone to a chronic course. In this pathology, the immune system is primarily affected.

Doctors draw the attention of patients to the fact that death does not occur from the immunodeficiency virus itself, as such.

A person dies from concomitant infections, to provide full protection against which the body is no longer able. It also causes death cancerous tumors, with which it is not able to fight reduced immunity.

In fact, the mechanism by which HIV infection affects the immune system is quite complex. According to doctors, patients do not need to understand it thoroughly. It is enough to know that the disease can reduce the level of immunity to critical values. As a result, the body will be unable to defend itself against various external influences, which will lead to death sooner or later.

How infection occurs

It is important to understand that HIV infection today is surrounded by a wide variety of myths.

Patients are very ill-informed about when it is possible to become infected, and when health is out of danger.

The first thing to remember is that HIV is very volatile in the environment. It means that pathogen able to live fully and for a long time only in human body. He does not tolerate heating above 50 degrees (dies instantly). Also not able to resist drying processes. Not all body fluids contain enough virus for infection to occur.

The greatest danger is:

• blood;
• pre-cum;
• sperm;
• discharge from the female vagina;
• lymph;
• breast milk.

If any of these fluids come into contact with mucous membranes in which there are microtraumas, or with skin affected by injuries, infection occurs.

It is also possible if the foreign fluid enters directly into the bloodstream. Saliva and tears, contrary to popular belief, do not pose a threat. Due to the characteristics of the virus and its low survival rate, it is transmitted in several ways:

• sexual way i.e. with unprotected sexual intercourse, which inevitably entails the contact of biological fluids and mucous membranes of the body susceptible to the pathogen;
• parenteral route i.e. transmission of the virus with blood during its transfusion or due to the use of non-sterile instruments for medical purposes;
• vertical path i.e. from mother to child (today, if a woman takes antiretroviral therapy and refuses to breastfeed, the chance of infection of a child during childbirth is minimized).

It is important to understand that if microtrauma or open wounds are required for infection through the skin, then this is not a necessary condition for infection through the mucous membrane. The difference is explained by the fact that the mucous membranes and skin of the human body have completely different structure. This difference must be taken into account.

How to suspect HIV

Many patients are interested in the question of what signs can usually be used to suspect infection with the human immunodeficiency virus.

• unreasonable increase in temperature of the systemic type, which cannot be explained by any other infection, and which persists for a long time, despite the measures taken for treatment;
• a strong increase in the size of the lymph nodes (in the first place, the nodes in the groin area suffer, but their involvement throughout the body is also possible);

• severe weight loss that cannot be explained by diets, stress, hormonal disruptions and other reasons;
• complaints of stool disorders that haunt the patient for a long time, and it is not possible to find the reason why they appeared;
• a pronounced tendency to the transition of any infectious diseases to chronic forms, and the nature of the pathogen does not matter much, both bacterial and viral pathologies are chronicled;
• diseases provoked by opportunistic microflora develop, which does not pose a threat to a person whose immunity is fully functional (for example, mycoplasmosis, ureaplasmosis, candidiasis, etc.).

The clinic of HIV infection is very non-specific, as doctors say. Because of this, it is often difficult to make a diagnosis. Many patients completely ignore the alarming symptoms, preferring not to seek medical help. Even if the disease greatly affects their general well-being.

It is important to understand that HIV infection for a long time may not make itself felt at all. And when the first signs appear, a person may not even associate them with the possibility of his infection and make attempts to be treated at home.

Diagnostic methods

Laboratory diagnosis of HIV has been developed for a long time and has been successfully used to diagnose this dangerous disease.

The disease cannot be identified by symptoms alone. Therefore, confirmation of the diagnosis on the basis of laboratory methods often plays a decisive role.

There are various methods for diagnosing HIV. In Russia, first of all, preference is given to immune blotting, as well as ELISA reactions. These methods are often used as screening methods, for example, when checking medical personnel.

ELISA systems

Often, patients ask their doctors how to start a diagnostic search for suspected infection with the human immunodeficiency virus.

Any competent doctor will say that preference should be given to enzyme immunoassay. It is this technique in Russia that is the first diagnostic stage.

The principle of ELISA is simple. Doctors created special proteins in the laboratory. They are able to detect and interact with antibodies produced by the body in response to exposure to HIV. Then a special indicator enzyme is added to the system, which changes its color. At the final stage, the material is processed using a special apparatus, and the doctor receives the final result.

IFA is very popular.

First of all, due to the fact that you can get results even if no more than a few weeks have passed since the introduction of the pathogen into the body.

It is important to understand that enzyme immunoassay does not determine the virus itself in the blood, but antibodies to it.

For many people, they may begin to develop later than two weeks, which may cause the result to be erroneous. There are several generations of ELISA tests.

The most modern and high-precision are those that belong to the 3rd and 4th generations. Doctors note that it is best, if there is a choice, to give preference to European reagents, since their accuracy reaches 99%. The terms for obtaining the results of the ELISA are on average from 2 to 10 days.

Why ELISA can be false

It is important to understand that enzyme immunoassay can give both false positive and false negative results. Although the risk of such a development of events is extremely small.

The patient can get false negative results if the test was taken too early and antibodies have not yet formed in the body.

To exclude such a reaction, patients are advised to take the analysis several times with different intervals of time.

A false positive test occurs in some diseases. For example, patients with:

• alcoholic hepatitis;
• myeloma in large numbers;
• some autoimmune diseases;
• women during pregnancy, etc.

In such diseases, human blood is replenished with antibodies. They can resemble HIV antibodies in structure, which confuses the reagents, provoking a reaction. Of course, test systems have become more and more sensitive in recent years. However, the problem of false results has not yet been fully resolved.

Immunoblotting

In modern conditions, it is impossible to make a positive diagnosis of HIV, relying only on ELISA. It is necessary to confirm the results obtained, which is performed using the reaction of immune blotting (immunoblotting, IB).

To perform IB, special test strips must be present in the laboratory. They are coated with viral proteins. Before analysis, the patient's blood taken from a vein is prepared in a special way.

The resulting biological material is added to the gel, in which proteins are separated by their weight. Then, a pre-prepared strip is lowered into the resulting mass.

The band gets wet (blotting occurs), bands are detected on it if the material contains HIV infection proteins. If proteins are absent, wetting does not change appearance stripes.

There are several interpretations of immunoblotting. However, by whatever method a particular hospital or laboratory performs the decoding, the probability of correct diagnosis is 99.9%.

Can immunoblotting give incorrect results, patients often wonder? Yes, it is possible, for example, if a patient has tuberculosis, is pregnant, or suffers from oncology.

PCR to help

PCR is another method that can diagnose the human immunodeficiency virus in blood and other body fluids where its concentration is quite high.

According to doctors, the polymerase chain reaction can give a positive result as early as 10 days after the first contact of the body with the infection.

It is important to understand that PCR in some cases gives false positive results. This is explained by the fact that the method has a very high sensitivity.

As a result, it often reacts to similar antibodies, indicating completely different pathological processes in the patient's body.

Despite its high sensitivity and low probability of false results, PCR is not widely used. This is explained by several factors. Firstly, to perform a polymerase chain reaction, special equipment is required, the price of which is quite high. Secondly, the personnel working with the equipment must be highly qualified, which can also cause difficulties. These features combined make PCR an expensive diagnostic method and, as a result, not accessible to everyone.

Despite the fact that PCR is not a screening method, it is used, for example, to test a newborn for infection with the human immunodeficiency virus.

Express systems for diagnostics

Doctors and scientists have spent a lot of effort to create rapid tests to assess HIV infection. According to doctors, when using these systems, it is possible to get a result within 15 minutes after the test has been carried out.

Rapid HIV tests are based on the principle of immunochromatography. The system usually includes a strip impregnated with special reagents.

The task of the patient is to apply blood, semen or any other biological fluid that may contain antibodies to the virus.

If they are found, then two colored bands will appear on the strip, one of which is control, and the other is diagnostic. If not detected, then only the control band will be detected.

It is important to understand that rapid tests do not give a 100% guarantee that a person is not infected or, on the contrary, is infected with HIV. In any case, the results obtained with their help must be confirmed in the laboratory using immunoblotting.

Express-type test systems are convenient for patients who want to calm themselves at home. However, as doctors note, even if with their help a person received a negative result, if you suspect negative changes in the body, you should still consult a doctor.

Which doctor should I contact if I suspect an infection?

Many patients are wondering which doctor they should contact if they suspect HIV infection. First of all, it is recommended to visit a venereologist. It is this medical worker who specializes in diseases that can be transmitted from person to person sexually.

The venereologist will be able to conduct a competent examination, collect an anamnesis and decide what examinations the patient needs for an accurate diagnosis. At his discretion, he can also refer the patient to the infectious diseases hospital. Especially if he still suspects he has HIV.

The human immunodeficiency virus is a common disease. Any person leading an active sex life can face it.

Knowledge of the features of the spread and diagnosis of this disease in modern realities is vital if the patient wants to maintain his health and longevity. Only a timely appeal to the doctor will allow you to take the infection under control and protect yourself from it!

Timely diagnosis of HIV infection becomes an extremely important measure, since earlier treatment can largely determine further development diseases and prolong the life of the patient. In recent years, there has been significant progress in the field of detecting this terrible disease: the old test systems are being replaced by more advanced ones, examination methods are becoming more accessible, and their accuracy is significantly increased.

In this article, we will talk about modern methods diagnosis of HIV infection, which is useful to know for the timely treatment of this problem and maintaining the normal quality of life of the patient.

Methods for diagnosing HIV

In Russia, for the diagnosis of HIV infection, a standard procedure is carried out, which includes two levels:

• ELISA test system (screening analysis);
• immune blotting (IB).

Other diagnostic methods can also be used:

• express tests.

ELISA test systems

At the first stage of diagnosis, a screening test (ELISA) is used to detect HIV infection, which is based on HIV proteins created in laboratories that capture specific antibodies produced in the body in response to infection. After their interaction with the reagents (enzymes) of the test system, the color of the indicator changes. Further, these color changes are processed on special equipment, which determines the result of the analysis performed.

Such ELISA tests are able to show results within a few weeks after the introduction of HIV infection. This analysis does not determine the presence of the virus, but detects the production of antibodies to it. Sometimes, in the human body, the production of antibodies to HIV begins after 2 weeks after infection, but in most people they are produced at a later date, after 3-6 weeks.

There are four generations of ELISA tests with different sensitivities. In recent years, III and IV generation test systems have been more frequently used, which are based on synthetic peptides or recombinant proteins and have greater specificity and accuracy. They can be used to diagnose HIV infection, monitor HIV prevalence, and ensure safety when testing donated blood. The accuracy of III and IV generation ELISA test systems is 93-99% (more sensitive are the tests that are produced in Western Europe - 99%).

To perform an ELISA test, 5 ml of blood is taken from the patient's vein. Between the last meal and the analysis should be at least 8 hours (as a rule, it is performed in the morning on an empty stomach). Such a test is recommended to be taken no earlier than 3 weeks after the alleged infection (for example, after unprotected intercourse with a new sexual partner).

The results of the ELISA test are obtained after 2-10 days:

• negative result: indicates the absence of HIV infection and does not require a referral to a specialist;
• false negative result: can be observed in the early stages of infection (up to 3 weeks), in the late stages of AIDS with severe immune suppression and with improper blood preparation;
• false positive result: it can be observed in some diseases and in case of improper blood preparation;
• positive result: indicates infection with HIV infection, requires an IB and the patient's referral to a specialist in an AIDS center.

Why can an ELISA test give false positive results?

False-positive results of an ELISA test for HIV can be observed with improper processing of blood or in patients with such conditions and diseases:

• multiple myeloma;
• infectious diseases provoked by the Epstein-Barr virus;
• state after ;
• autoimmune diseases;
• against the background of pregnancy;
• condition after vaccination.

For the reasons described above, non-specific cross-reacting antibodies may be present in the blood, the production of which was not provoked by HIV infection.

In recent years, the frequency of false positive results has significantly decreased due to the use of III and IV generation test systems, which contain more sensitive peptide and recombinant proteins (they are synthesized using in vitro genetic engineering). After the use of such ELISA tests, the frequency of false positive results has significantly decreased and is about 0.02-0.5%.

A false positive result does not mean that a person is infected with HIV. In such cases, WHO recommends another ELISA test (mandatory IV generation).

The patient's blood is sent to a reference or arbitration laboratory marked "repeat" and tested on a IV generation ELISA test system. If the result of the new analysis is negative, then the first result is recognized as erroneous (false positive) and IB is not carried out. If the result is positive or doubtful during the second test, the patient is required to undergo IB in 4-6 weeks to confirm or refute HIV infection.

immune blotting

A definitive diagnosis of HIV infection can only be made after a positive immune blotting (IB) result is obtained. For its implementation, a nitrocellulose strip is used, on which viral proteins are applied.

Blood sampling for IB is performed from a vein. Then it undergoes special treatment and the proteins contained in its serum are separated in a special gel according to their charge and molecular weight (the manipulation is carried out on special equipment under the influence of an electric field). A nitrocellulose strip is applied to the blood serum gel and blotting (“blotting”) is carried out in a special chamber. The strip is processed and if the materials used contain antibodies to HIV, they bind to the antigenic bands on IB and appear as lines.

IB is considered positive if:

• according to American CDC criteria - there are two or three lines gp41, p24, gp120 / gp160 on the strip;
• according to American FDA criteria - there are two lines p24, p31 and a line gp41 or gp120 / gp160 on the strip.

In 99.9% of cases, a positive IB result indicates HIV infection.

In the absence of lines - IB is negative.

When identifying lines with gp160, gp120 and gp41, IB is doubtful. Such a result can be detected when:

• oncological diseases;
• pregnancy;
• frequent blood transfusions.

In such cases, it is recommended to perform a second study using a kit from another company. If, after additional IB, the result remains doubtful, then follow-up is necessary for six months (IB is performed every 3 months).

polymerase chain reaction

The PCR test can detect the RNA of the virus. Its sensitivity is quite high and it allows detecting HIV infection as early as 10 days after infection. In some cases, PCR can give false positive results, because its high sensitivity can also react to antibodies to other infections.

This diagnostic technique is expensive, requires special equipment and highly qualified specialists. These reasons do not allow it to be carried out during mass testing of the population.

PCR is used in such cases:

• to detect HIV in newborns who were born to HIV-infected mothers;
• to detect HIV in the "window period" or in case of doubtful IB;
• to control the concentration of HIV in the blood;
• for the study of donor blood.

Only by the PCR test, the diagnosis of HIV is not made, but is carried out as an additional diagnostic method to resolve disputes.

Express Methods

One of the innovations in HIV diagnostics has become rapid tests, the results of which can be assessed in 10-15 minutes. The most efficient and accurate results are obtained with immunochromatographic tests based on the principle of capillary flow. They are special strips on which blood or other test fluids (saliva, urine) are applied. In the presence of antibodies to HIV, after 10-15 minutes, a colored and control strip appears on the test - a positive result. If the result is negative, only the control line appears.

As with ELISA tests, rapid test results should be confirmed by IB analysis. Only then can a diagnosis of HIV infection be made.

There are express kits for home testing. The OraSure Technologies1 (USA) test is FDA approved, available without a prescription, and can be used to detect HIV. After the test, in case of a positive result, the patient is recommended to undergo an examination in a specialized center to confirm the diagnosis.

The remaining tests for home use have not yet been approved by the FDA and their results can be very questionable.

Despite the fact that rapid tests are inferior in accuracy to IV-generation ELISA tests, they are widely used for additional testing of the population.

You can get tested for HIV infection at any polyclinic, the Central Regional Hospital or at specialized AIDS centers. On the territory of Russia, they are held absolutely confidentially, or anonymously. Each patient can expect to receive medical or psychological advice before or after the analysis. You will have to pay for HIV tests only in commercial medical institutions, and in public clinics and hospitals they are performed free of charge.

For information on how you can get HIV infection and what myths exist about the possibilities of getting infected, read

The diagnosis of HIV infection is important factor on the way to a speedy recovery, the process helps to ensure timely therapy for the patient.

HIV infection is caused by the human immunodeficiency virus, which actively affects the entire immune system of the patient, because of which the latter is inhibited and AIDS develops without timely intervention (the acquired immune deficiency syndrome known to everyone). Understanding how the disease process proceeds and how it affects the entire body helps to better understand why early and accurate diagnosis is important. There is a huge risk that diseases will arise that are not usually characteristic of people who have a normal, strong immune system. Without timely intervention, this condition will lead to death.

Symptoms

Everyone should know the symptoms of this common infection and its course. The danger lies in the fact that HIV is a slowly progressing disease, which in the early stages has non-specific signs, to some extent similar to the manifestations of mononucleosis. And then for some time the disease is asymptomatic. Given this, you need to know additional clinical indications for testing a patient for HIV:

Diagnostics

Laboratory diagnosis of HIV infection, as a rule, has 3 main directions and goals:

1. Direct determination of the presence of HIV infection in the body.
2. Determining which of the 8 stages the disease is in, and identifying concomitant diseases in a weakened body.
3. Prediction of possible progression in the clinical course of the disease and constant monitoring of ongoing treatment with the help of screening tests for antibodies. Watching for possible side effects from taking antiretroviral drugs.

In the first months, especially in the absence of proper treatment, a person infected with HIV will experience a rapid increase in the load on the entire body (that is, the content of infected RNA in plasma increases). Due to the fact that there is a rapid infection of not only cells, but also blood with lymph nodes, it becomes possible to determine proviral DNA.

The problem with making a diagnosis is that antibodies to HIV do not appear immediately, but the ELISA method and immunoblotting remain the most reliable.

In immunology, this phenomenon is called the serological window - this is the most important period from the onset of infection to the appearance of such an amount of antibodies that can be detected using tests. How long this moment lasts depends on the state of the immune system of each person individually, but on average it lasts from 2 to 12 weeks. At this time, tests will show that the person is healthy, but in fact he is already infected. Sometimes it can take up to 3 years, while HIV antibodies, while in the human body, do not show any signs of activity (this happens in 10% of those infected).

Diagnosis of HIV infection includes 3 stages of blood tests carried out in a special laboratory. The first is called screening, with its help it is determined whether there are antibodies against HIV proteins.

The second way of diagnosing is the reference method, with the help of special methods they clarify or confirm the primary screening result. The third diagnostic stage, which is also expert, is needed for the final verification of HIV infection markers that were identified at the previous stages of laboratory diagnostics. That is, it is needed in order to both confirm and exclude a possible error. All these tests are quite expensive and complex, and therefore are performed only in laboratories with special equipment. In studies of blood serum, it is noted that sometimes the reaction is either false positive or indefinite. This happens in pregnant women and in those who have some autoimmune diseases, in which case the tests are taken again after a month and a half, during which time the concentration of specific antibodies in the body will reach required level(if any) and the result will be more accurate.

If at least one of the serological methods of research showed a positive result for HIV, then further examination should be dynamic and regular until the functions of the immune system are fully restored.

Stage Definition

The disease is defined as follows: Approximately 2 weeks after the suspected infection, the immunoblotting method is used, this assay has the highest sensitivity, approximately 97%. If the result is negative, another, even more sensitive method is used - this is a polymerase chain reaction (PCR) or ELISA. Theoretically, this hypersensitive assay can detect one DNA per 10 mg of medium. It happens that immunoblotting shows a negative result, and ELISA is positive. This suggests that at this stage there is an initial period of seroconversion, that is, the concentration of specific antibodies in the body will increase and re-analysis using immunoblotting after a while will show a positive result.

How it works? Using the polymerase chain reaction method, a large number of copies of the nucleic acid are made, because the virus is in a protein shell. Among the resulting copies, the cells affected by the virus are determined by their distinctive structure and with the help of labeled enzymes. The problem with this method is that this diagnostic method is too expensive and is not routinely used unless the patient is willing to pay for it individually or in a private clinic.

Laboratory diagnosis of HIV infection helps to distinguish 5 stages of how the pathology develops. These stages go through the same way, the difference is only in the time frame, since everything depends on the state of the immune system of each individual person.

• incubation latent stage;
• stage of primary obvious signs;
• asymptomatic course of the disease;
• acute HIV infection without secondary diseases;
• acute form of the disease with secondary pathologies;
• clinically latent stage (lasts up to 7 years);
• stage of secondary diseases;
• the terminal stage, when practically human systems and organs are irreversibly affected by the disease.

According to the analyzes and the number of affected cells in it, according to general condition doctors can quite accurately determine at what stage of the disease a person is.

incubation period. At this time, viruses and affected HIV nucleic acids are not yet detected in the blood, therefore, having fallen into the period of the asymptomatic serological window, a person may not know about his illness.

Stage of primary manifestations. At this time there are characteristics, which were listed above, antibodies are formed in the body.

Asymptomatic stage. The most dangerous, during this period of the disease, even those signs that appeared in the second stage subside, the disease disappears without obvious symptoms.

Acute HIV infection without secondary disease. When the patient's blood is re-examined, wide-plasma leukocytes are found with a parallel decrease in the number of lymphocytes. An increased content of the former indicates inflammation in the body, most patients have an acute infection.

Acute HIV infection with secondary diseases. Due to the rapid decrease in lymphocytes, a persistent immunodeficiency develops in the body, against which other various diseases. For example, candidiasis, pneumonia, allergies, all kinds of infections, tonsillitis and more.

latent stage. Immunodeficiency progresses, the disease worsens, and the person himself loses an average of 10% of his body weight.

Stage of secondary diseases. This penultimate period also has its 3 stages, the so-called 4A, 4B, 4C. In the absence of proper treatment, the strength and capabilities of the body are greatly depleted.

Terminal stage. The critical decrease in CD-cells is less than 0.05-109 cells/L. The concentration of antibodies is practically determined.

Blood tests for HIV in children

For a long time after birth, the baby's blood contains maternal antibodies to HIV infection. A blood test that is done in the first month of a baby's life may not confirm infection, but the absence of antibodies to HIV does not mean that the virus has not crossed the placenta. Such children should be observed for the first 3 years, making appropriate tests.

To avoid error as much as possible, the results of laboratory responses should be considered only in conjunction with the data of the general clinical examination.

Modern diagnostics of HIV infections almost completely excludes a possible error, except for some points, it is important to take advantage of this as early as possible.