HIV diagnosis

What tasks do the laboratories of the AIDS Centers perform?

The functions of the laboratories include the following main tasks:

Diagnosis of HIV infection

Control (monitoring) of the effectiveness of treatment provided to people living with HIV (PLHIV)

Diagnosis of HIV drug resistance

HIV diagnosis is a process that includes a series of laboratory tests with the mandatory use of various diagnostic test systems and methods. The need for a series of tests is primarily due to the simple fact that today there is no ideal method that guarantees absolutely accurate separation of infected patients from uninfected persons. The most reliable data is achieved by a combination of several tests (methods), some of which better identify HIV-infected patients, and others - better identify uninfected. At the first stage, laboratories use the most sensitive test systems of the latest (fourth) generation. The probability of a false negative result when using these test systems is extremely small, therefore, when receiving a negative result, AIDS Centers immediately issue a conclusion: No antibodies to HIV have been detected.

However, a positive result is not absolutely accurate proof of the presence of HIV infection. In Kazakhstan, the overall prevalence of HIV infection is quite low (<0.05%). The probability of detecting an HIV-infected patient among the general population is less than the probability of obtaining a false positive result (the permissible limit is 2%). Therefore, a positive result requires confirmation. To do this, the laboratories of the AIDS Centers conduct additional tests that allow you to "filter out" true-positive results from false-positive ones. At the last stage, an immunoblot test is used, which guarantees maximum reliability of positive results. Based on this result, doctors can make a final conclusion about the presence of HIV infection in the patient.

Monitoring the effectiveness of antiretroviral therapy. In Kazakhstan, people living with HIV receive free treatment in the form of antiretroviral therapy (ART). The effectiveness of ART depends very much on a number of factors: compliance with the medication regimen, the primary resistance of the virus to a particular drug, or the rate of occurrence of mutant resistant forms. Therefore, all PLHIV receiving ART undergo regular examination in the laboratories of regional and city AIDS centers for quantitative determination of HIV RNA (viral load) and quantitative determination of CD4+/CD8+ T-lymphocyte levels.

The viral load test allows you to determine how effectively drugs suppress the reproduction of the virus. A test for CD4+/CD8+ T-lymphocytes shows the state of the patient's immunity. If the viral load is at a low level, and the number of CD4+ cells is growing, then the chosen treatment regimen is effective. If not, it is necessary to make appropriate adjustments.

Diagnosis of HIV drug resistance. The problem of the emergence of HIV drug resistance is inevitable when implementing a large-scale treatment program for PLHIV. In the case when therapy turns out to be ineffective, and this is not related to the patient's commitment to treatment, studies are conducted on the basis of the AIDS RC to identify and genotyping mutant forms of the virus. These studies allow us to determine which drugs can no longer suppress the reproduction of the virus, and thus adjust the treatment regimen.

What is an immunoblot and why can we trust its positive results?

The human immunodeficiency virus consists of a number of proteins (antigens), to each of which specific antibodies are produced in an infected patient. Unlike tests performed at the first stages (ELISA, IHLA, rapid tests), the immunoblot can determine which specific HIV antigens a patient has antibodies to.

According to the criteria of the World Health Organization (WHO), a positive result can be established when antibodies to at least two of the three surface proteins of the virus (gp) are detected. Therefore, the use of an immunoblot minimizes the probability of false positive results.

Fig. 1. Example of an immunoblot

gp160, gp120, gp41, p66, p24, p17 are virus proteins. The appearance of a dark transverse line on the test strip indicates the presence of antibodies to this protein in the patient's body.Example of an immunoblot

There are two types of immunoblot. The first, the so-called Western Blot, is made from proteins of real, but previously destroyed viruses grown in cell culture. The advantage of the Western blot is that all HIV proteins are present in it, and we can see the full picture of the process of generating specific antibodies in the patient's body. However, the use of an expensive culture accordingly affects the price of this test. The second type of immunoblot, a linear immune test, was developed in order to reduce the cost of confirmatory analysis. Recombinant (artificially created) proteins are used in linear immune tests. Since a number of HIV proteins are absent in tests of this type, we get a fragmentary picture. For example, in linear immune tests, gp160 protein is missing - one of the three surface proteins on the basis of which the final decision is made, which makes this test less informative. Therefore, the Western blot remains today the "gold standard" for confirming the diagnosis of HIV infection.

How reliable are the negative results of the immunoblot?

Due to insufficient sensitivity (compared to ELISA, IHLA or rapid tests), negative results of the immunoblot should be treated with caution. Therefore, when receiving a negative or uncertain result of the immunoblot, AIDS Centers prescribe the patient to undergo a second examination in two weeks. As a rule, this period is enough for the patient's body to develop enough antibodies to the main proteins of the virus. However, in some cases, this process may take several months, so the patient may be invited to undergo an examination several more times, up to the final establishment or exclusion of the diagnosis of HIV infection.

How is the safety of donated blood ensured?

Screening of blood donors for HIV (i.e. mandatory examination of each blood donation, each donor) is carried out not by regional AIDS, but by blood centers. At the same time, the fourth-generation IHL/ELISA methods are used, which make it possible to simultaneously detect viral antigen and antibodies to HIV. In addition, blood samples are examined using the polymerase chain reaction method (in Fig. 2 it is designated as NAT - nucleicacidamplificationtechnology, Eng.), which allows detecting HIV RNA as early as 10 days after infection. Up to this point, HIV infection is not detected by any tests.

Fig. 2. Detection of HIV infection using tests of various formats and generations during the natural course of infection.Detection of HIV infection by means of tests

Upon receiving a positive result of any of the tests, the potentially infected donor blood is destroyed, and the donor himself is removed from the opportunity to donate blood in the future. At the same time, the diagnosis of HIV infection is not made to the donor without conducting confirmatory studies. To make a final diagnosis, a blood sample of the donor is sent to the AIDS RC for further research according to the approved algorithm of testing for HIV infection.

How is HIV-2 diagnosed in Kazakhstan?

According to the available epidemiological data, not a single case of HIV-2 infection has been registered in the CIS today. Nevertheless, in all laboratories of the regional AIDS centers of Kazakhstan and blood centers, test systems are used that can simultaneously detect both HIV-1 and HIV-2 infection. In addition, the great similarity of the structure of viruses of the first and second types provides a cross-reaction in the immunoblot at the confirmation stage. If HIV-2 infection is suspected, the AIDS RC laboratory has an appropriate immunoblot at its disposal to detect specifically antibodies to the human immunodeficiency virus of the second type.

How much does an HIV test cost?

According to the tariffs for medical services within the guaranteed volume of free medical care approved by the order of the Ministry of Health of the Republic of Kazakhstan, the cost of HIV testing is 1413.99 tenge.

Can private medical organizations perform HIV research?

In order for the population to have wide access to HIV testing, medical organizations of all forms of ownership can conduct the first stage of laboratory diagnostics of HIV infection. At the same time, the Ministry of Health will provide for qualification requirements and the obligation to provide statistical reporting.

Press service of the RC AIDS