What is HIV screening. Goals of HIV testing and screening

The analysis will be ready within 1 day, excluding Sunday (except for the day of taking the biomaterial). You will receive results by email. email as soon as it's ready.

Preparation for analysis

Do not take a blood test immediately after radiography, fluorography, ultrasound, physiotherapy.

24 hours before blood sampling:

Limit fatty and fried foods, do not take alcohol.

Eliminate heavy physical activity.

From 8 to 14 hours before donating blood, do not eat, drink only clean still water.

Do not smoke for 60 minutes prior to blood sampling.

15-30 minutes before blood sampling to be in a calm state.

Analysis Information

Index

Hospital screening can detect hepatitis B and C viruses, HIV, syphilis in a person.

Hospital screening is a standard set of studies before an operation or hospitalization to prevent infection of personnel and people who will be in the same room with the patient. Often long time after infection, a person may not know about his illness. This is dangerous for him and for those around him. Including for staff during hospitalization or surgery.

The analysis is carried out in order to eliminate the risks of infection of personnel during hospitalization and other people in the ward.

It is prescribed by a doctor before hospitalization.

Research method - Immunochemiluminescent analysis (ICLA)

Material for research - Blood serum

Composition and results

• Composition of a comprehensive study

Hospital screening (HIV, syphilis and hepatitis B and C)

A set of tests required for hospitalization:

If you are planning an operation, then in addition to the analyzes included in this complex, you must perform others. The list of tests will be prescribed by the doctor, or you can choose a complex that includes a standard set of tests for hospitalization and surgery.

The complex of these tests is designed to detect infections transmitted with blood and other body fluids before hospitalization. The purpose of performing these tests before hospitalization is to protect others, both staff and patients in the hospital, from infection.

And if there is a disease, take into account the possible complications.

If a positive or doubtful result of any of the tests is obtained, confirmatory tests are performed.

Only with a positive result of confirmatory tests, a positive result is issued. To do this, the analysis period can be extended additionally up to 7 days.

A positive result of any of the analyzes of this complex does not always mean that the patient has a disease.

The diagnosis of the disease is made by the doctor on the basis of a clinical examination, additional data laboratory tests and the results of other studies.

Interpretation of the results of the study "Hospital screening (HIV, syphilis and hepatitis B and C)"

The interpretation of test results is for informational purposes, is not a diagnosis and does not replace the advice of a doctor. Reference values ​​may differ from those indicated depending on the equipment used, actual values ​​will be indicated on the results sheet.

A positive result of any of the tests may indicate the presence of a current disease or a past disease.

A negative test result may indicate the absence of a current or past infection, but early disease cannot be ruled out.

If you receive a doubtful result of any of the tests, the test must be repeated after 10 to 14 days.

Unit of measurement:

a qualitative test, the result is given in the form: positive, negative, questionable

Reference values: Negative result

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Timely diagnosis of HIV infection becomes an extremely important measure, since earlier treatment can largely determine the further development of the disease and prolong the life of the patient. AT last years Significant progress is being made 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 for diagnosing HIV infection, which are useful to know for timely treatment of this problem and maintaining the normal quality of life of the diseased.

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 for more than later dates 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 on early dates 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 HIV infection, requires an IB and the patient's referral to a specialist at the 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%.

Revealing is 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

The final diagnosis of HIV infection can only be established after a positive result is obtained. immune blotting(IB). 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 additional method diagnostics 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 only have to pay for HIV tests 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

Diagnosis of HIV is one of the primary tasks that the employees of the dermatovenerological dispensary, as well as the staff of the polyclinic, face.

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 diseases prone to 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. Also, cancerous tumors become the cause of death, with which reduced immunity is unable to fight.

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 highly volatile in environment. This means that a pathogenic microorganism is 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 human body have completely different structures. 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;
• strong increase lymph nodes in size (in the first place, 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.

Exist various methods HIV diagnosis. 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 specialize 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!

Critical to the diagnosis of HIV infection laboratory diagnostics, which consists in the detection of antibodies to HIV in the blood by ELISA, followed by confirmation of positive results by IB. This method of diagnosing HIV infection makes it possible to identify HIV-infected individuals with an efficiency of 99%.

Indications for the use of various laboratory research and features of the interpretation of the results

Currently, for the screening stage of diagnosing HIV infection, kits of reagents of the third and fourth generations based on the ELISA method are used. Distinctive feature tests of the fourth generation is the possibility of simultaneous detection of hypertension (p24) and total AT, while tests of the third generation allow you to determine only AT. Where possible, fourth-generation tests should be preferred due to their higher diagnostic sensitivity and the ability to detect infection in individuals during the serological window.

A negative result in the detection of antibodies to HIV by ELISA does not always indicate the absence of infection. A serious problem is those cases when the test is carried out during the serological window, i.e. in the first weeks after infection, when antibodies to HIV have not yet been developed in sufficient quantities. In some individuals, the serological window may extend for several months; therefore, if there is evidence of exposure to HIV-infected people, repeat tests are usually carried out after 2–3 months. False-negative results of detection of antibodies to HIV using ELISA can be obtained in the terminal stage of the disease, characterized by severe damage. immune system with a deep violation of the process of formation of antibodies.

A positive result of detection of antibodies by ELISA indicates the likelihood of contracting HIV infection, but sometimes this result can be a false positive, for example, if a person has tumors, allergic diseases, during pregnancy, with autoimmune diseases, significant changes in indicators biochemical research blood, some chronic diseases. In such cases, additional research in an expert laboratory is required.

If a positive result of detection of antibodies to HIV by ELISA is obtained, its confirmation is required. At the first stage of confirmation, the analysis is repeated in the same test system in two wells - this eliminates technical errors. If the result is confirmed, the determination of antibodies by ELISA in the patient's serum is repeated using two reference sets of reagents. If a positive result is obtained in at least one of these studies, the third stage of confirmation is undertaken: a study by the IB method, which allows the detection of antibodies to individual HIV antigen proteins.

The results obtained by the IB method are interpreted as positive, doubtful and negative. The results are considered negative (negative) if no antibodies to any of the HIV antigens are found in the test serum or there is a weak reaction with the p17 protein. The most compelling reason for positive reaction is the detection of antibodies to HIV envelope proteins (glycoproteins gp41, gp120, gp160). The result is considered positive if antibodies to any two HIV glycoproteins are detected. If there is a reaction with only one of the envelope proteins, in combination with a reaction with other proteins or without it, the result is considered doubtful, in this case it is recommended to conduct tests to detect p24 antigen or HIV DNA / RNA. If p24 hypertension or HIV DNA/RNA is detected, retest using IB is performed 2 weeks after the first indeterminate result and every 2 weeks thereafter until a positive result is obtained in the confirmatory test. If, 6 months after the first examination, indeterminate results are again obtained, and the patient has no risk factors for infection and clinical symptoms HIV infection, the result is regarded as a false positive.

Often, after 1–3–6 months from the moment of obtaining a doubtful result, antibodies to all HIV antigens appear one after another in the blood serum. In this case, a dubious result is evidence of the initial stage of HIV infection. In some cases, doubtful results of IB are observed in uninfected individuals who have antibodies in their bodies that are similar to true antibodies to HIV.

One of the indirect signs of HIV infection is a selective decrease in CD4+ T-helper cells due to the fact that HIV has a tropism for the CD4 cell receptor. However, these changes may be absent at certain stages of HIV infection, have individual variations in different patients, and also occur in other diseases. So, in adult patients who are in the latent stage of the disease, the number of CD4 + lymphocytes usually exceeds 0.5. 109/l, which corresponds to the values ​​in healthy people.