1. Serological methods detection of antibodies (AT) to HIV is the standard for diagnosing HIV infection (ELISA test systems based on synthetic peptides have almost 100% sensitivity and specificity). ELISA allows you to detect HIV Ags, which may be indicators of early infection or, conversely, late - advanced development of HIV infection (p24 Ag)
2. Confirmatory tests— immunoblotting (IB), indirect immunofluorescence (IIF) and radioimmunoprecipitation (RIP).
a) WHO recommends that serum containing antibodies to two envelope proteins and one of the internal proteins of HIV be considered positive. Patients who are positive by ELISA but have indeterminate results by IB should be evaluated clinically and assessed by other means, medical examination, immunologically and after 3 - 6 months, their blood serum must be tested for antibodies to HIV.
b) indirect immunofluorescence (IIF) method - used as a confirmatory test in many laboratories or as a screening test.
c) radioimmunoprecipitation is a highly sensitive and specific method based on the use of amino acids labeled with radioactive isotopes. The method is highly sensitive for the detection of antibodies to surface proteins and is therefore highly specific, since these components of the virus are present in almost all HIV-infected individuals after seroconversion.
3. Molecular biological methods: method of molecular hybridization of nucleic acids, PCR
1) as an alternative and additional confirmatory method for detecting the presence of a virus in the body in relation to serological methods laboratory diagnostics;
2) as the first method specific analysis when diagnosing early HIV infection, when specific antiviral antibodies are not yet available;
3) for diagnosing HIV infection of newborns from HIV-infected mothers;
4) to determine the viral load and prescribe specific antiretroviral therapy and monitor its implementation;
5) as a clarifying method in case of unclear serological results and in case of discrepancy between serological and cultural tests;
6) when studying sexual partners of HIV-infected persons;
7) as a method of differential diagnosis of HIV-1 and HIV-2;
4. Virological method.
1. Principles of antiretroviral therapy: treatment should begin before the development of significant immunodeficiency; initial therapy should include combinations of at least three drugs; modification of therapy should consist of replacing or adding at least two new drugs; It is extremely important to measure the level of CD4+ cells and viral load; a decrease in viral load to a level below the detection limit of sensitive methods reflects the optimal effect of treatment.
2. There are three groups of modern antiretroviral drugs:
a) nucleoside reverse transcriptase inhibitors (NRTIs): zidovudine (azidothymidine, retrovir); didanosine (ddI, Videx); zalcitabine (ddC, hivid); stavudine (zerit, d4T); lamivudine (3TC, epivir); abacavir; adefovir; combivir (zidovudine + abacavir); trizivir (zidovudine+lamivudine+abacavir); adefovir (nucleotide reverse transcriptase inhibitors).
b) non-nucleoside reverse transcriptase inhibitors (NNRTIs): delaverdine(rescriptor); nevirapine(viramune); efavirenz
c) protease inhibitors (PI): saquinavir; ritonavir (norvir); indinavir (Crixivan); nelfinavir (Viracept); amprenavir (Agenerase); lopinavir (aluviran); Kaletra (lopinavir + ritonavir).
3. Monotherapy with any drug cannot provide sufficiently pronounced and long-lasting suppression of HIV replication. Moreover, with monotherapy, there is an increased risk of the emergence of resistant strains and the development of cross-resistance to drugs of the same group. The only exception is the use of zidovudine as monotherapy to reduce the risk of perinatal transmission of HIV.
4. The most important criterion for the effectiveness of therapy is the dynamics of the viral load, which should be determined: without treatment - every 6-12 months, during treatment - every 3-6 months, and also 4-8 weeks after the start of antiviral therapy.
In addition to antiretroviral therapy, treatment for secondary diseases is necessary.
34.3 AIDS (clinical variants, opportunistic diseases).
Opportunistic diseases- severe, progressive diseases that develop against the background of increasing immunosuppression and do not occur in a person with a normally functioning immune system (AIDS-defining diseases).
a) first group- these are diseases that are characteristic only of severe immunodeficiency (CD4+ level< 200 кл/мкл) и поэтому определяют клинический диагноз: 1. Кандидоз пищевода, трахеи, бронхов. 2. Внелегочный криптококкоз. 3. Криптоспоридиоз с диареей более 1 месяца. 4. Цитомегаловирусная инфекция с поражением различных органов, помимо печени, селезенки или лимфоузлов. 5. Инфекции, обусловленные вирусом простого герпеса, проявляющиеся язвами на коже и слизистых оболочках. 6. Саркома Капоши у лиц, моложе 60 лет. 7. Первичная лимфома мозга у лиц, моложе 60 лет. 8. Лимфоцитарная интерстициальная пневмония и/или легочная лимфоидная гиперплазия у детей в возрасте до 12 лет. 9. Диссеминированная инфекция, вызванная атипичными микобактериями с внелегочной локализацией. 10. Пневмоцистная пневмония. 11. Прогрессирующая многоочаговая лейкоэнцефалопатия. 12. Токсоплазмоз с поражением головного мозга, легких, глаз у больного старше 1 месяца.
b) second group- diseases that can develop both against the background of severe immunodeficiency, and in some cases without it: 1. Bacterial infections, combined or recurrent in children under 13 years of age (more than two cases over 2 years of observation): septicemia, pneumonia, meningitis, lesions bones or joints, abscesses caused by Haemophilus influenzae, streptococci. 2. Disseminated coccidioidomycosis (extrapulmonary localization). 3. HIV encephalopathy 4. Histoplasmosis, disseminated with extrapulmonary localization. 5. Isosporosis with diarrhea that persists for more than 1 month. 6. Kaposi's sarcoma in people of any age. 7. B-cell lymphomas (except Hodgkin's disease) or lymphomas of unknown immunophenotype. 8. Extrapulmonary tuberculosis. 9. Salmonella septicemia is recurrent. 10. HIV dystrophy.
The most common are Pneumocystis pneumonia, cryptococcal meningoencephalitis, generalized cytomegalovirus infection (encephalitis, retinitis, esophagitis, hepatitis, colitis), sepsis of mixed etiology, generalized form of Kaposi's sarcoma, pulmonary tuberculosis.
All these diseases occur with damage to one or more organs and systems: the brain, lungs, liver, gastrointestinal tract and are severely progressive. AIDS-defining diseases appear in various combinations, and even adequate therapy does not bring the expected effect.
Clinical variants of AIDS: infectious, neuro-, oncological AIDS, depending on the prevalence of different clinics.
HIV: diagnosis and treatment, prevention
Acquired immunodeficiency syndrome has been one of the key problems of modern society for more than forty years. Therefore, HIV diagnosis is now attracting a lot of attention and resources. After all, the sooner a virus that destroys the body’s immune system is detected, the higher the chances of avoiding death.
The abbreviation HIV hides the definition of the human immunodeficiency virus - one of the most dangerous among those currently existing. Under its influence, all the protective properties of the body are deeply suppressed. This, in turn, leads to the occurrence of various malignant tumors and secondary infections.
HIV infection can progress in different ways. Sometimes the disease destroys a person in 3-4 years, but in some cases it can last more than 20 years. It is worth knowing that this virus is unstable and dies quickly if it is outside the host’s body.
HIV can be transmitted artificially, through blood contact and through a biocontact mechanism.
If there has been a single contact with a carrier of the virus, then the risk of infection will be low, but with constant interaction it increases significantly. Diagnosis of HIV infection is something that should not be neglected, especially when changing sexual partners
It is worth paying attention to the parenteral route of infection. It can occur during blood transfusions of contaminated blood, injections using needles that are contaminated with the blood of HIV-infected people, as well as during non-sterile medical procedures (tattoos, piercings, dental procedures using instruments that have not been properly treated).
At the same time, it is worth knowing that there is no need to be afraid of contact and household transmission of the virus. But the fact remains: a person is highly susceptible to HIV infection. And if a subject over the age of 35 becomes infected, then the development of AIDS occurs significantly faster than in those who have not yet overcome the thirty-year mark.
Of course, the best way to identify the problem, or lack thereof, is through an HIV diagnosis. But what reasons could a person have for leading healthy image life, go and check yourself for infection? Naturally, such an initiative must be justified in some way. Therefore, it is important to know what symptoms may indicate destructive processes that suppress the immune system.
It is unlikely that it will be possible to identify the incubation stage of the virus without a blood test, since the body at this time does not yet react in any way to hostile elements.
The second stage (primary manifestations) can also go unnoticed without the help of a doctor. But sometimes active replication of the virus occurs, and the body begins to react to this - fever, various polymorphic rashes, linear syndrome and pharyngitis are noted. At the second stage, it is possible to add secondary diseases such as herpes, fungal infections, pneumonia, etc.
The third, latent stage is characterized by a gradual increase in immunodeficiency. Due to the fact that the cells of the protective system die, the dynamics of their production increases, and this makes it possible to compensate for significant losses. At this stage there are several lymph nodes belonging to different systems can become inflamed. But strong painful sensations however, are not observed. On average, the latent period lasts from 6 to 7 years, but can last up to 20.
During the stage of secondary diseases, which is the fourth stage, concomitant infections of fungal, bacterial protozoal, viral origin appear, as well as malignant formations. All this occurs against the background of severe immunodeficiency.
Methods for diagnosing HIV infection
Talking about deep oppression defense mechanisms body due to exposure to the virus, it is worth noting that the patient’s future in this case directly depends on timely and accurate diagnosis.
For this purpose in modern medicine Various test systems are used, which are based on immunochemiluminescent and enzyme-linked immunosorbent blood tests. These techniques make it possible to determine the presence of antibodies belonging to different classes. This result helps to significantly increase the information content of methods of analytical, clinical specificity and sensitivity when working with infectious diseases.
Also interesting is the fact that it was the polymerase chain reaction method that made it possible to bring HIV diagnosis to a fundamentally new level. A variety of biological materials are suitable for research: blood plasma, biopsy, scraping, serum, cerebrospinal or pleural fluid.
If we talk about laboratory research methods, they are primarily focused on identifying several key diseases. We are talking about HIV infection, tuberculosis, all sexually transmitted infections, and viral hepatitis.
Molecular genetic and serological tests are also used to identify the immunodeficiency virus. In the first case, the RNA of the virus and the DNA of the provirus are determined; in the second case, antibodies to HIV are analyzed and the P24 antigen is detected.
In clinics that use, so to speak, classic methods diagnostics, a standard serological testing protocol is predominantly used.
Early diagnosis of HIV
This type of determination of the fact of infection is necessary in order to identify the threat of damage to the immune system as early as possible. This, firstly, allows you to avoid the spread of infection, and secondly, influence the disease in the initial stage.
If we consider the example of Russia, a clinical classification of HIV infection was introduced in the army and navy of the Russian Federation. This has yielded positive results: the process of early clinical diagnosis has become much easier.
Common symptoms indicating possible damage to the immune system include headache, night sweats and unmotivated fatigue. It is also possible to develop fever accompanied by signs of tonsillitis. This means that the temperature rises to 38 degrees or higher, and at the same time the tonsils become enlarged, and pain appears during swallowing. All this is complemented by rapid weight loss. Moreover, these symptoms are often complex.
In some cases, HIV infection early stages may manifest itself in the form of various changes in skin condition. We are talking about spots, roseola, pustules, furunculosis, etc. Early HIV diagnosis also includes working with symptoms such as generalized or limited enlargement of peripheral lymph nodes.
If there is simultaneous growth of several lymph nodes, lasting for three months or more, and in different groups, with the exception of groin area, that is, there is every reason to suspect a virus of the human immune system.
Speaking about diagnostics in more late period, you need to pay attention to the manifestation secondary immunodeficiency, which often occurs under the guise of various clinical symptoms. We are talking about the following manifestations:
- unmotivated generalized peripheral lymphadenopathy;
- arthralgia of unknown etiology, which has a wavy course;
- ARVI (ARI), inflammatory lesions of the lungs and respiratory tract, which make themselves felt quite often;
- fevers of unknown origin and prolonged low-grade fever;
- general intoxication, which manifests itself through unmotivated weakness, fatigue, lethargy, etc.
- carrying out early diagnosis HIV infection;
- clarifying the presence of questionable results as a result of an immunoblotting study;
- identification of a specific stage of the disease;
- monitoring the effectiveness of treatment aimed at suppressing the virus.
HIV diagnosis on late stage includes examination for a disease such as Kaposi's sarcoma, which is manifested by the appearance of multiple neoplasms, often in the upper part of the body in young people, followed by dynamic development and metastasis.
Polymerase chain reaction
When considering various methods for diagnosing HIV infection, this is worth paying special attention to. It should immediately be noted that this blood test can be aimed at quantitative and qualitative characteristics.
The purpose of this method of detecting a virus can be defined as the following:
If we talk about primary infection, it should be noted that this technique makes it possible to determine HIV RNA in the patient’s blood after 14 days from the moment of infection. This is a very good result. In this case, the result of the study itself will have a qualitative expression: either positive (the virus is present) or negative.
Quantitative PCR expression
This type of polymerase chain reaction is used to determine the likely rate of progression of AIDS and to predict the patient's life expectancy.
Quantitative determination of HIV RNA cells in the blood makes it possible to understand when the disease enters the clinical stage.
It is worth paying attention to the fact that laboratory diagnostic methods for HIV give more accurate results if the biomaterial required for analysis is determined correctly and its collection is carried out competently.
In order to carry out high-quality monitoring of infected people, it is necessary (if possible) to use A complex approach to study the patient's immune status. We are talking about the quantitative and functional determination of all parts of the defense system: cellular, humoral immunity and nonspecific resistance as such.
Laboratory diagnostics
Increasingly, in modern laboratory conditions, a multi-stage method for assessing the state of the immune system is used. This technique often involves determining a subpopulation of immunoglobulins and lymphocytes in the blood. This means that the CD4/CD8 cell ratio is taken into account. If the result shows less than 1.0, then there is reason to suspect immunodeficiency.
Laboratory diagnosis of HIV infection must include this test, since this virus is characterized by selective damage to CD4 lymphocytes, which leads to a noticeable violation of the above-mentioned ratio (less than 1.0).
To assess the immunological status, doctors can conduct a test for the presence of “gross” or general defects in the humoral and cellular immunity system. We are talking about hypogammaglobulinemia or hypergammaglobulinemia in terminal stage, as well as a decrease in the production of cytokines, an increase in the concentration of circulating immune complexes, and a weakening of the response of lymphocytes to mitogens and antigens.
It is worth paying attention to the fact that laboratory diagnosis of HIV has two key stages:
- Screening laboratory. If a positive result was obtained in ELISA (enzyme-linked immunosorbent assay), then it is repeated two more times in the same system and without changing the serum. In the event that two of the three examinations lead to the detection of the influence of the virus, the serum is sent for further testing to a reference laboratory.
- The second stage, which includes laboratory diagnostic methods for HIV infection, is determining the state of the immune system. It is carried out in the reference laboratory mentioned above. Here, the positive serum is again tested in ELISA, but using a different test system, which differs from the previous one in the composition of antigens, antibodies or the format of the tests themselves. If a negative result is determined, a repeat test is carried out in a third test system. If the impact of the virus was ultimately not detected, then the absence of HIV infection is recorded. But if the result is positive, the serum is examined in a linear or immunoblot.
Ultimately, such an algorithm leads to positive, neutral or negative results.
Every citizen should know that HIV diagnostics are available to them. AIDS can be identified in institutions of the private, municipal or state health care system.
Naturally, identifying the virus would be of little use in the absence of various methods of influencing the infection. And although at the moment there is still no vaccine that could completely neutralize the virus, competent diagnosis, treatment of HIV and subsequent prevention can significantly improve the patient’s condition, thereby prolonging his life. This thesis is confirmed by the fact that the average life expectancy of men who began timely HIV treatment is 38 years. Women who start fighting the immunodeficiency virus live an average of 41 years.
After diagnosis has been made, HIV treatment comes down to the use of several techniques. One of the most common is active antiretroviral therapy, also known as HAART. If this type of treatment is applied promptly and correctly, you can significantly slow down the development of AIDS or stop it altogether.
The essence of HAART is that several pharmaceuticals are used simultaneously, the purpose of which is to influence various mechanisms of development of the immunodeficiency virus.
After various HIV diagnostic methods have determined the fact of infection, medications that have the following effects can be used:
It is difficult to overestimate the importance of such measures to influence the disease as diagnosis, treatment, and prevention of HIV infection. Therefore, the best thing that can be done after a positive test result for infection is to immediately begin to fight the disease. Another method that can help do this is virological treatment.
In this case, we are talking about the use of drugs that do not allow the virus to attach to the T-lymphocyte and enter the body. These drugs are called penetration inhibitors. A concrete example is Celsentry.
Viral protease inhibitors can be used to suppress HIV. The purpose of this group of drugs is to prevent new lymphocytes from becoming infected. These are drugs such as Viracept, Reyataz, Kaletra, etc.
The third group of topical medications are reverse transcriptase inhibitors. They are needed to block the enzyme that allows the virus RNA to multiply in the nucleus of the lymphocyte. Such methods can have a significant impact on a problem such as HIV infection. Diagnosis, treatment and prevention of AIDS is the work of qualified doctors, so the algorithm for using drugs should be drawn up by them.
If necessary, immunological and clinical interventions can also be used.
The World Health Organization suggests following methods fight against HIV infection:
To ensure that HIV diagnosis does not reveal the presence of the virus, you must follow simple rules security:
Thanks to the fact that HIV diagnosis does not stand still, thousands of people have the opportunity to start treatment on time and significantly increase their life expectancy. The main thing is not to ignore obvious symptoms and not be afraid to go to the doctor.
Laboratory diagnosis of HIV infection
The following are subject to testing for HIV infection:
2. Persons with a suspected or confirmed diagnosis of: 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 infection of other organs, except the liver, spleen, lymph nodes in patients older than 1 month; cytomegalovirus retinitis with vision loss; herpetic infection, causing multifocal ulcers that do not heal within 1 month, or bronchitis, pneumonia, esophagitis; disseminated or extrapulmonary histoplasmosis; isosporosis with diarrhea for more than 1 month; widespread or extrapulmonary tuberculosis; pulmonary tuberculosis in adults or adolescents over 13 years of age; extrapulmonary tuberculosis; another disease caused by mycobacteria other than M. tuberculosis disseminated or extrapulmonary; pneumonia caused by pneumocystis; progressive multifocal leukoencephalopathy; Salmonella (except Salmonella typhi) septicemia, recurrent; brain toxoylosis in children older than 1 month; Kaposi's sarcoma; lymphoid interstitial pneumonia in children under 13 years of age; Burkitt's lymphoma; immunoblastic lymphoma; primary brain lymphoma; wasting syndrome, hepatitis B, HBsAg carriage; infectious mononucleosis; recurrent herpes zoster in people over 60 years of age; sexually transmitted diseases.
In a highly specialized laboratory the following is carried out:
a) determination of antibodies, antigens and immune complexes circulating in the blood; cultivating the virus, identifying its genomic material and enzymes;
b) assessment of the functions of the cellular component of the immune system. The main role belongs to serological diagnostic methods aimed at determining antibodies, as well as pathogen antigens in the blood and other biological fluids body.
HIV antibody testing is carried out to:
a) safety of blood transfusions and transplantations;
b) surveillance, testing in order to monitor the prevalence of HIV infection and study the dynamics of its prevalence in a certain 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 built on a three-stage principle. The first stage is screening, intended to perform primary blood tests for the presence of antibodies to HIV proteins. The second stage is referential - allows, with the help of special methodological techniques clarify (confirm) the primary positive result obtained at the screening stage. The third stage is the expert stage, intended for the final verification of the presence and specificity of markers of HIV infection 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 that allow identifying HIV-infected people with a sufficient degree of reliability:
ELISA test (enzyme-linked immunosorbent assay) for detection of 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 that allows you to differentiate HIV-1 and HIV-2;
Antigenemia p25 test, effective in initial stages 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 in the positive mixture is tested. This method does not lead to a loss of sensitivity in both ELISA and immunoblot, but reduces labor costs and the cost of the initial examination by 60-80%.
During the primary serodiagnosis of HIV infection, total antibodies are determined using 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 the basis for a conclusion about the HIV seropositivity of the subject. 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 at all by a special neutral protein; cross interaction with HIV immunosorbent proteins of various proteins present in the blood of persons with certain, often autoimmune, pathological processes such as multiple sclerosis, SLE, tuberculosis; with frequent donations, infectious and oncological diseases, burns, pregnancy, repeated blood transfusions, organ and tissue transplants, as well as persons on hemodialysis; with the presence of rheumatoid factor in the blood, which often provokes 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 exo-or endogenous retroviruses that have not yet been identified). Since anti-p24 is synthesized without fail in the early stages of HIV seroconversion, further immunological monitoring of individuals with antibodies to HIV gag proteins is carried out, as well as their exclusion from donation.
The sensitivity and specificity of enzyme immunoassays are constantly increasing. As a result, fourth-generation ELISAs are not inferior in their diagnostic capabilities to immunoblotting 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 diagnosis, allowing one to make a final conclusion about the HIV positivity or negativity of the subject.
There is a clear correlation between the results of studying sera in immunoblotting and ELISA - double-positive sera in ELISA with different test systems in 97-98% of cases then turn out to be HIV-positive in immunoblotting. If the sera turned out to be positive in the ELISA in only one of the two test systems used, in the immunoblot they are detected positive only in 4% of cases. In 5% of cases, when conducting confirmatory studies in individuals with positive data, ELISA immunoblot can give “uncertain” results, and among them, in approximately 20% of cases, “uncertain” results are caused by 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 blood serum for HIV-2 infection.
Evaluation of immunoblotting results is carried out strictly in accordance with the instructions supplied with the test system. If the instructions do not provide guidance on how to interpret the results, WHO criteria should be used.
If positive research results are obtained at the reference stage of laboratory diagnosis of HIV infection and a negative result of the immunoblotting test is obtained, a mandatory repeated expert diagnosis is carried out 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, 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 and the need to equip special premises 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 pre-multiplied nucleotide sequences specific to 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. In 2-3 hours, PCR allows you to obtain millions of copies of a specific region of the virus. During HIV infection, from cellular RNA, including the RNA of the virus, if it was reproduced in a 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 identified and characterized quantitatively , as in relation to belonging to the HIV genome, using a radioactive or other probe label, establishing the homology of DNA and virus-specific amino acid sequences. The sensitivity of PCR is the detection of viral genes in one out of five thousand cells.
PCR, including quantitative, can be used only to determine the viral load in plasma to decide whether to start drug treatment for a patient or change antiretroviral drugs. PCR cannot be recommended for diagnosing HIV infection, since even the most cutting-edge methods and reagents can determine the viral load not lower than a certain level - 50 copies/ml. And the complexity of PCR testing and its high cost (about $200) negate its widespread use as a method of routine laboratory diagnosis of HIV infection. Thus, PCR remains indispensable only for assessing the viral load in plasma in patients with an already established diagnosis of HIV infection in order to resolve the issue of patient therapy.
The stages of laboratory diagnosis of HIV infection are shown schematically in Fig. 1.
Rice. 1. Stages of laboratory diagnosis of HIV infection
During HIV infection, there is a period of “dark laboratory window” when the amount of antibodies against HIV is insufficient for the sensitivity of 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 during examination donated blood from persons staying in the mentioned period of HIV infection. Therefore, in most countries of the world, a system of using blood only after it has been stored for 3-6 months has been introduced in order to carry out mandatory re-examination for HIV infection of donors of these doses of blood and its components.
Stage primary manifestations 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 infected people can be detected in the blood by ELISA already 2 weeks after infection and can be detected up to the 8th week. Next in clinical course HIV infection is characterized by a second increase in the level of p24 protein in the blood; it occurs during the formation of the AIDS stage.
The appearance of complete seroconversion, when a high level of specific IgG antibodies to the HIV structural proteins gp41, p24, gpl20 is recorded in the peripheral blood, significantly facilitates the diagnosis of HIV infection. Most commercial kits are designed to indicate just such antibodies.
Difficulties in detecting antibodies in patients with HIV infection may arise during periods of massive viremia and antigenemia, when the existing 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 binding of HIV virions and soluble proteins by antibodies, therefore, test systems with hypersensitivity or modifications of assay methods that include the step of releasing antibodies from immune complexes.
Despite the abundance of specific markers of HIV infection, the most often 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 wide range antibodies to various, primarily to structural, proteins of HIV.
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 determination of the content of CD4+ lymphocytes has become: a decrease in the level below 200 cells/mm3 is the main criterion for diagnosing AIDS. All HIV-infected individuals with a CD4+ lymphocyte count of 200 cells/mm3 or below are considered to require both antiviral therapy and prophylaxis against Pneumocystis pneumonia. And although 1/3 of HIV-infected people with a number of CO4+ lymphocytes less than 200 cells/mm3 do not have clinical manifestations, experience has shown that their symptoms develop in the next 2 months, so they are all regarded as patients at the AIDS stage.
Diagnosis of HIV infection
How to find out if a person has HIV? The most common method for diagnosing HIV infection is enzyme-linked immunosorbent assay (ELISA). Enzyme-linked immunosorbent test systems are used to detect antibodies to HIV in blood serum.
HIV infection is confirmed by two different tests - a screening test and a confirmatory test. Due to their high sensitivity, screening tests may produce false-positive results. Therefore, usually when receiving the primary positive result the same blood sample is taken and the screening test is repeated a second time, and if it is again positive, only then is a different type of confirmatory test performed. Confirmatory tests are performed only on blood samples that repeatedly test positive (are “reactive”).
The most common screening test is enzyme-linked immunosorbent assay (ELISA). Typically, immunoblotting is used as a confirmatory test. The combination of two different types of tests ensures that the results obtained are “highly accurate”.
Screening test systems use artificially created HIV proteins that “catch” specific antibodies produced by the body in response to viral proteins. Once antibodies are captured, they "can be detected by reagents that are used in conjunction with an indicator, such as an enzyme, that causes a color change." The color changes are read by a machine, which determines the result. Immunoblotting works in a similar way, but uses an electric field to distinguish different components based on their molecular weight. This allows antibodies to specific viral antigens to be detected, which are then depicted on paper as distinguishable “stripes”. Modern test systems can detect HIV infection in 3-5 weeks in most people.
If there was a risk of HIV infection, when can you get a test?
The enzyme-linked immunosorbent assay (ELISA), which is used to diagnose HIV, can only show results several weeks after infection. This type of analysis determines not the virus itself, but antibodies to it. In some people, antibodies are present in sufficient quantities in the blood after 2 weeks. However, in most people it takes longer for antibodies to form (seroconversion). For the test result to be sufficiently reliable, it is necessary that about 3 months have passed since the risky situation. Sometimes the formation of antibodies takes longer - from 3 to 6 months.
If the test result is negative after 3 months, is it necessary to retest after 6 months?
For the vast majority of people, the test is quite reliable after 3 months (in most people, antibodies appear even earlier). You can completely exclude the possibility of infection by getting tested after 6 months.
How long should I wait for test results?
This depends on the characteristics of the laboratory in which the testing is carried out. The ELISA test can be done within the same day, but in most laboratories this period can range from 1-2 days to 2 weeks. Considering that waiting for results can be a very unpleasant period, it is best to clarify this issue in advance, before taking the test. You can also find out whether weekends and holidays will affect the timing of the test.
How reliable is a positive test result?
Sometimes ELISA has false positive results (in about 1% of cases), the cause of such a result may be pregnancy, various viral infections, or simple accident. After receiving a positive result, more accurate test- immunoblot, based on the results of which a diagnosis is made. A positive immunoblot result after a positive ELISA is 99.9% reliable - this is the maximum accuracy for any medical test. If the immunoblot is negative, it means that the first test was false positive, and in fact the person does not have HIV.
What is an uncertain (doubtful) result?
If ELISA is positive or negative, then immunoblot can be positive, negative or indeterminate. Indeterminate immunoblot result, i.e. the presence of at least one protein to the virus in the immunoblot can be observed if the infection occurred recently and there are still few antibodies to HIV in the blood, in which case the immunoblot will become positive after some time. Also, an uncertain result may appear in the absence of HIV infection with hepatitis, some chronic diseases metabolic nature, or during pregnancy. In this case, either the immunoblot will become negative or the cause of the indeterminate result will be found.
Do I need to take an HIV test when applying for a job?
According to the legislation of the Russian Federation, HIV testing can be mandatory only for blood donors, foreign citizens and stateless persons wishing to enter the territory of the Russian Federation for a period of more than three months, as well as medical personnel working directly with blood; persons in prison. All other citizens take an HIV test voluntarily.
HIV infection– a disease resulting from infection with the human immunodeficiency virus (HIV).
HIV is an RNA virus belonging to the retrovirus family.
A common property of retroviruses is the presence of an enzyme - reverse transcriptase (revertase), which “removes” a genetically accurate copy in the form of DNA from RNA. Based on morphology, genome structure and other characteristics, HIV belongs to the family of lentiviruses, that is, viruses of slow infections. The general features of diseases caused by viruses of this family include: a long incubation period that does not have exact dates (from 1 month to 10 years or more); inconspicuous, asymptomatic onset of the disease; slowly increasing clinical picture; pathogenesis is mediated through the immune system and high speed genetic variability of the virus. All this greatly complicates the diagnosis, treatment and prevention of HIV infection.
There are currently two known types of HIV: HIV-1 and HIV-2. The disease caused by HIV-2 is characterized by slow dynamics and a longer course.
Epidemiology and transmission routes:
HIV infection is an anthroponosis, the only source of the pathogen for a person is a virus carrier and an AIDS patient.
Viral particles (virions) are present in all biological fluids of the body, but in varying concentrations. The highest levels of the virus are in the blood and seminal fluid.
The virus is transmitted in three ways:
- from mother to fetus/newborn.
HIV is not transmitted through ordinary household contacts or through airborne droplets. There have been no recorded cases of HIV transmission through the bites of blood-sucking insects.
However, HIV is not as contagious as other STIs. Thus, of more than 1,600 sexual partners of HIV-infected people examined, only 15% became infected with this virus.
The development of HIV infection is determined by two interacting factors: the main pathogenic property of HIV, which is to weaken the immune system of an infected person, and the specific immune response of the body that develops during the course of the disease.
HIV is pantropic, but its main target cells are T-helper cells, which carry hundreds of CD4+ receptor molecules on their membrane. In the body, the virus transforms from a less aggressive state to a more aggressive one, which is expressed in a progressive decrease in the number of CD4+ lymphocytes in the blood until their complete disappearance and leads to worsening clinical picture.
From the moment of infection to the appearance of specific antiviral antibodies, it usually takes 6-8 weeks. The period between infection and the appearance of detectable antibodies to HIV in the blood serum is called the “window” period.
On the one hand, the immune system is a target for the virus, on the other hand, it itself produces specific antibodies to it. At the same time, the development of autoimmune processes occurs in the immune system, which aggravate the process of destruction of cells and tissues of the body.
HIV infection is characterized by the absence of a specific clinical picture, and its diagnosis is usually made on the basis of a carefully collected medical history in combination with a number of signs confirmed by laboratory diagnostics. In 1983, WHO developed certain criteria by which the presence of HIV infection can be determined if serological diagnostics are unavailable (Bangui criteria). These include:
- loss of body weight by more than 10% of the original;
— chronic diarrhea for more than one month;
- prolonged fever for one month (constant or intermittent).
- persistent cough for more than one month;
- generalized itchy dermatitis;
- history of herpes zoster;
- chronic progressive or disseminated herpetic infection(herpes simplex);
A diagnosis of HIV infection using these criteria can be made to a patient if he is found to have simultaneously at least two “big” signs and one “small” sign. A sufficient basis for making a diagnosis of AIDS may be the discovery of generalized Kaposi's sarcoma or cryptococcal meningitis in a patient. Due to the low sensitivity and specificity of these criteria, WHO subsequently required serological confirmation of the diagnosis.
Clinical classification of HIV infection:
Stage of primary manifestations:
A. acute febrile phase;
B. asymptomatic phase;
B. persistent generalized lymphadenopathy.
Stage of secondary diseases:
A. Weight loss less than 10 kg, superficial bacterial, viral, fungal infections skin and mucous membranes, herpes zoster, repeated pharyngitis, sinusitis.
B. Progressive weight loss of more than 10 kg, unexplained diarrhea, fever for more than 1 month, hairy leukoplakia, pulmonary tuberculosis, repeated or persistent bacterial, fungal, viral, protozoal lesions internal organs(without dissemination) or deep lesions of the skin and mucous membranes, repeated and disseminated herpes zoster, localized Kaposi's sarcoma.
The presence of antibodies to HIV depending on the stage of the disease.
Antibodies to HIV in the blood
HIV test result
II. Primary manifestations
B. Asymptomatic phase
III. Secondary diseases
After the virus enters the body, it multiplies in the blood. In 50% of infected individuals, a prodromal state may develop during this period, accompanied by a rise in body temperature to 38.5-39.5 ° C and other mononucleosis-like symptoms and lasting from three to 10 days. This condition passes, reminiscent of the recovery period after a flu infection.
Starting from 6-8 weeks of illness, an increase in the level of antibodies in the blood occurs, that is, seroconversion. During this period, generalized lymphadenopathy and minor immunodeficiency may develop, but in some patients the clinical manifestations of HIV infection are minimal. With severe acquired human immunodeficiency syndrome (AIDS), opportunistic infections of internal organs rapidly develop, affecting nervous system. Activation of saprophytic flora is observed on the skin and mucous membranes. Kaposi's sarcoma and other tumors develop. Infections such as tuberculosis, syphilis, deep mycoses, etc. may become more active. A characteristic disease for HIV-infected people is Pneumocystis pneumonia. In some patients, the liver and spleen are enlarged, which is an unfavorable sign indicating rapid progression of the process. There are cerebral forms of HIV infection - such as meningitis caused by yeast fungi, toxoplasmic brain abscesses, acute and subacute encephalitis, isolated brain tumors (lymphomas). Patients may present with various vascular lesions.
Nonspecific diagnostic methods include the following: determination of the content of T-lymphocyte subpopulations in the blood, assessment of the activity of the reactivity of peripheral blood T-lymphocytes or biopsy material.
Specific diagnostic methods include:
— detection of provirus DNA or RNA of the HIV virus in human cells by PCR;
— detection of mature infectious virions in biological fluids and cells;
— determination of soluble viral proteins (antigens);
— determination of antibodies to HIV (ELISA, immunoblot, agglutination reaction, radioimmunoprecipitation).
The most common diagnostic screening method is ELISA. A negative result may indicate:
— about the absence of infection;
— about conducting the study before the onset of seroconversion (during the “window” period or during other periods of disappearance of the antibody titer).
Positive results can be true or false. False positives can be obtained when examining patients with chronic infectious, autoimmune or oncological diseases, uninfected pregnant women, patients after blood transfusions and patients with chronic alcoholism. The earliest time for detection of antibodies to HIV is 3-4 weeks from the date of infection.
Confirmatory analysis. Immunoblot.
After the screening test, all positive results are checked in another enzyme immunoassay system, and then in a more sensitive test - immunoblot. Sera confirmed by this test can be considered true positive.
Before conducting an HIV test, the patient must be counseled (pre-test counseling) on the reasons why the test is necessary, and after receiving the result, accordingly, post-test counseling must be carried out in order to explain the result of the study. Confidentiality must be maintained at all stages of diagnosis and subsequent treatment.
There are four main approaches to the treatment of HIV infection: etiological, immunostimulating, immunoreplacement and pathogenetic (against secondary infections).
Nucleotide analogues or inhibitors of other classes have the ability to suppress viral reverse transcriptase. The first drug to treat AIDS patients was a nucleotide analogue, azidothymidine. The drug causes side effects, affecting primarily hematopoiesis, and in most patients, with long-term use (more than 6 months), resistance to it develops. Currently, over 10 new drugs are used - protease and reverse transcriptase inhibitors. Significantly complicates the creation process effective drugs rapid rate of HIV mutation in the body, accompanied by the emergence of treatment-resistant strains.
Only a combined approach can limit viral replication and prevent the development of drug resistance. Triple antiretroviral therapy (a combination of three drugs based on two nucleoside analogues and protease inhibitors) has become standard.
Produced by several different methods. It would seem that there is nothing easier than identifying this disease through blood sampling. But it is not so. The diagnosis of HIV can indeed be detected in this way, but further research is carried out using different methods. They largely determine what treatment will be prescribed to the patient and what measures will be taken subsequently. Among the most common and highly effective methods are screening analysis and immunoblotting. Each of them should be considered in more detail.
AIDS diagnosis: screening analysis
A screening test or ELISA test method is used at the initial stage of diagnosing HIV infection. When developing this method, virus proteins were artificially created in the laboratory. They react to antibodies in a special way. The latter are produced in the body when cells infected with a terrible disease appear in it. Laboratory diagnosis of HIV in this case is made using artificial enzymes. When they interact with antibodies, they turn a certain color. A strip with an indicator, after blood gets on it, is placed under a special device, with the help of which it is possible to determine whether a person has this disease or not. Modern methods for diagnosing HIV, including ELISA, make it possible to determine the fact of infection or its absence with high accuracy. But, like all equipment, the screening analysis apparatus has an error. That is why, if necessary, the patient retakes the test.
It is important to know that the ELISA test is one of the earliest methods for determining the presence of the immunodeficiency virus in the body. HIV infection is a diagnosis that can only be detected several weeks after infection. When infected cells enter the bloodstream, the body's immune system begins to actively resist. Antibodies are produced, which are detected by laboratory testing after two or three weeks. Early diagnosis of HIV infection using an ELISA test allows one to detect antibodies to the immunodeficiency virus in a person’s blood. This is its main difference from other modern methods.
It is worth noting that some people have antibodies to this disease begin to be produced at a later date. From the moment of infection to the start of this process, it can take three to six weeks. This is why medical experts recommend undergoing a screening test four to five weeks after unprotected sexual intercourse or other reason for suspecting accidental infection.
Methods for laboratory diagnosis of HIV infection by ELISA have been developed over a long period of time. To date, there are four generations of tests. The most accurate and effective of them are those that were developed most recently. Laboratory diagnosis of HIV infection and AIDS using the third and fourth generation of ELISA tests is carried out using recombinant proteins and peptides. The sensitivity of these tests to antibodies produced by the body is 92 - 93%. We are talking about Russian research methods. Europeans have learned to do similar tests with a sensitivity of 99%.
Modern methods of laboratory diagnosis of HIV infection based on ELISA are used not only to detect the presence of the disease. Using a screening analysis, it is possible to monitor the spread of the immunodeficiency virus, as well as collect test material before drawing blood from donors.
ELISA is a standard method for diagnosing HIV infection: how is it done, why does it give a false result?
Diagnosis of HIV and AIDS using ELISA is a standard procedure. The patient's blood is taken from a vein. Five milliliters of material is sufficient for analysis. Clinical 
HIV types 2 and 1 are diagnosed at least eight hours after ingestion. Doctors recommend doing it in the morning on an empty stomach. The results of the full study are known in two or three days. Express screening is performed in less time. As a rule, this only takes a few hours. However, the error in this case increases. Express diagnosis of HIV is necessary in emergency cases, for example, when a patient needs urgent surgery. Such an analysis must be performed before unscheduled surgical interventions, because if a patient has an immunodeficiency virus, doctors observe increased safety measures. Clinical diagnosis of HIV infection in a short period of time is also necessary in cases where donated blood must be collected quickly to save another patient.
There are cases when a person was diagnosed with AIDS or HIV, but as a result it was not confirmed, or vice versa. Why does this happen in the case of the ELISA test? A false negative result may be due to the fact that the blood was improperly prepared for the test. Sometimes the reason for this is improper execution of its collection. A false negative result when verifying the diagnosis of HIV infection is not confirmed even if the materials for the study were taken too early. After all, at least three weeks must have passed after infection. There are cases when the result of detection of the immunodeficiency virus is false positive. It's connected with general condition immune and hormonal systems of the human body. In most cases, the patient experiences diseases that are the result of a false positive result. We are talking about alcoholic hepatitis, in which the liver produces special enzymes, which can cause an incorrect diagnosis of HIV. Pregnancy and some autoimmune diseases, along with multiple myeloma can also cause a false positive result. This list can include patients on dialysis and people who were vaccinated shortly before the differential diagnosis of HIV.
Speaking about screening analysis, it is important to note that this research method requires confirmation. Doctors, before making a diagnosis of HIV based on it, always send the patient for immune blotting.
Basic methods of laboratory diagnosis of HIV infection: immunoblotting
AIDS, the diagnosis and treatment of which are closely interrelated, is detected in several ways. As mentioned above, one ELISA test is not enough to finally determine the diagnosis. Differential diagnosis of HIV infection in this case is complemented by immunoblotting. In modern medicine it is called the final confirmatory method of diagnosis. In this case, proteins contained in the patient’s blood are used for research. They are separated in a special gel, after which laboratory workers have the opportunity to study the molecular composition of the blood.
The time it takes to diagnose HIV using this method ranges from one to three days. For the study, blood is taken from the subject’s vein and placed on a tester with a gel. The result, which is called into question, can occur during pregnancy, the presence of oncological processes, or tuberculosis. A false negative reaction to the test can occur if the test is carried out incorrectly or if it is carried out too early. At least three weeks must pass from the moment of infection. After all, the time it takes for HIV to be diagnosed directly depends on the state of the immune system.
Other methods for diagnosing AIDS and HIV
Radiation diagnostic methods for AIDS are used, as a rule, in the terminal or secondary stages. With their help, it is possible to identify changes that occur in the body due to secondary diseases or opportunistic infections.
Bioresonance diagnostics of HIV, which is also called non-linear scanning, is used mainly in private clinics to detect the immunodeficiency virus. Official medicine considers this method to be insufficiently accurate and effective. Perhaps the improvement of nonlinear diagnostics in the future will make it possible to identify this terrible diagnosis already in the incubation period.
Diagnosis of HIV infection: serological method and its features
It's comparative new technique, in which laboratory criteria for diagnosing HIV infection are based on the antigen-antibody principle. In the case of the immunodeficiency virus, a search for antibodies to the virus occurs in the human body. To do this, an artificially derived antigen is used, to which antibodies must react. Specific serological markers of HIV infection cause specific changes in the composition of the blood. It is worth noting that this research method is most effective in the acute stage, which ends with seroconversion. This is followed by an asymptomatic latent period, during which it is not easy to find the antigen.
Reference diagnostics of HIV infection: description and features
HIV reference values are considered the most accurate in identifying a diagnosis. This research method combines ELISA test and immunoblotting. The HIV diagnostic reference laboratory allows samples to be collected and subsequently processed in two ways. This allows you to get the most accurate result within 24 hours. Rechecking the analysis obtained in the reference laboratory is necessary only if the data from the ELISA test and immunoblotting contradict each other. This is enough a rare event, which most often occurs in people with the above-described concomitant diseases.
Timely diagnosis of HIV infection becomes an extremely important measure, since early initiation of treatment can largely determine the further development of the disease and prolong the patient’s life. In recent years, there has been significant progress in identifying this terrible disease: older test systems are being replaced by more advanced ones, examination methods are becoming more accessible, and their accuracy is significantly increasing.
In this article we will talk about modern methods diagnosis of HIV infection, knowledge of which is useful for timely treatment of this problem and maintaining a normal quality of life for the patient.
HIV diagnostic methods
In Russia, a standard procedure is carried out to diagnose HIV infection, which includes two levels:
- ELISA test system (screening analysis);
- immunoblotting (IB).
Other methods can also be used for diagnosis:
- rapid 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. Next, these color changes are processed using special equipment, which determines the result of the analysis performed.
Such ELISA tests can show results within a few weeks after the introduction of HIV infection. This test 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 varying sensitivities. In recent years, third and fourth generation test systems have been increasingly 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 generation III and IV ELISA test systems is 93-99% (tests produced in Western Europe are more sensitive - 99%).
To perform an ELISA test, 5 ml of blood is taken from the patient’s vein. At least 8 hours must pass between the last meal and the analysis (usually it is performed in the morning on an empty stomach). It is recommended to take such a test no earlier than 3 weeks after the suspected infection (for example, after unprotected sexual intercourse with a new sexual partner).
ELISA test results are obtained in 2-10 days:
- negative result: indicates absence of HIV infection and does not require contacting a specialist;
- false negative result: may be observed on early stages infection (up to 3 weeks), with late stages AIDS with severe immunosuppression and improper blood preparation;
- false positive result: can be observed in some diseases and in case of improper blood preparation;
- positive result: indicates HIV infection, requires IB and the patient contacting a specialist at the AIDS center.
Why can an ELISA test give false positive results?
False-positive HIV ELISA test results can occur due to improper blood processing or in patients with the following conditions and diseases:
- multiple myeloma;
- infectious diseases caused by the Epstein-Barr virus;
- state after ;
- autoimmune diseases;
- against the background of pregnancy;
- condition after vaccination.
For the reasons described above, nonspecific 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 decreased significantly due to the use of generation III and IV test systems, which contain more sensitive peptide and recombinant proteins (they are synthesized using genetic engineering in vitro). After the introduction of such ELISA tests, the frequency of false positive results decreased significantly and is about 0.02-0.5%.
A false positive result does not mean that the person is infected with HIV. In such cases, WHO recommends conducting another ELISA test (necessarily IV generation).
The patient’s blood is sent to a reference or arbitration laboratory with the mark “repeat” and tested using a IV generation ELISA test system. If the result of the new analysis is negative, then the first result is considered erroneous (false positive) and IS is not carried out. If the result is positive or questionable during the second test, the patient must undergo IB after 4-6 weeks to confirm or refute HIV infection.
Immune blotting
A definitive diagnosis of HIV infection can only be made after a positive immunoblotting (IB) result is obtained. To carry it out, a nitrocellulose strip is used, on which viral proteins are applied.
Blood sampling for IB is performed from a vein. Next, it undergoes special processing and the proteins contained in its serum are separated in a special gel according to their charge and molecular weight (manipulation is carried out using 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 the 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 the American FDA criteria, the strip has two lines p24, p31 and a line gp41 or gp120/gp160.
In 99.9% of cases, a positive IB result indicates HIV infection.
If there are no lines, the IB is negative.
When identifying lines with gr160, gr120 and gr41, IB is doubtful. This result may occur when:
- oncological diseases;
- pregnancy;
- frequent blood transfusions.
In such cases, it is recommended to repeat the study using a kit from another company. If after additional IB the result remains doubtful, then observation is necessary for six months (IB is carried out every 3 months).
Polymerase chain reaction
A PCR test can detect the RNA of the virus. Its sensitivity is quite high and it allows detecting HIV infection within 10 days after infection. In some cases, PCR may give false positive results, because it high sensitivity may also react to antibodies to other infections.
This diagnostic technique is expensive and requires special equipment and highly qualified specialists. These reasons do not make it possible to carry out mass testing of the population.
PCR is used in the following cases:
- to detect HIV in newborns born from 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.
The PCR test alone does not make a diagnosis of HIV, but is carried out as a additional method diagnostics to resolve controversial situations.
Express methods
One of the innovations in HIV diagnostics is rapid tests, the results of which can be assessed within 10-15 minutes. The most effective and accurate results are obtained using immunochromatographic tests based on the principle of capillary flow. They are special strips on which blood or other test fluids (saliva, urine) are applied. If antibodies to HIV are present, after 10-15 minutes a colored and control strip appears on the test - a positive result. If the result is negative, only the control strip appears.
As with ELISA tests, the results of rapid tests must be confirmed by IB analysis. Only after this can a diagnosis of HIV infection be made.
There are rapid home testing kits available. The OraSure Technologies1 test (USA) is FDA approved, available over the counter and can be used to detect HIV. After the test, if the result is positive, the patient is recommended to undergo examination at a specialized center to confirm the diagnosis.
Other tests for home use have not yet been approved by the FDA and their results may 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 take tests to detect HIV infection at any clinic, central district hospital or specialized AIDS centers. On the territory of Russia they are carried out absolutely confidentially, or anonymously. Each patient can expect to receive medical or psychological consultation before or after the test. 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.
Read about the ways in which you can become infected with HIV and what myths exist about the possibilities of becoming infected.
