HIV test (clinical analyzes)

Content

Introduction

HIV (human immunodeficiency virus) infection has a chronic course, may not create disturbances (be asymptomatic) for many years and can only be discovered by performing the specific test (Video).

In particular, the "ascertainment (diagnosis) of HIV infection is carried out by searching the blood for specific antibodies and the antigen called p24. The measurement of the amount of virus circulating in the blood (viremia-viral load), on the other hand, is mainly carried out to follow the progress of the infection over time (monitoring).

To avoid infecting other people and to start the necessary treatments as soon as possible, it is essential that anyone who has had behaviors potentially at risk (read the hoax) of infection carries out the HIV test in the manner recommended by the Ministry of Health (Video).

When planning a pregnancy, or at the beginning of the gestation period, it is recommended to carry out the HIV test in order to be able to implement, if the result is positive, all possible procedures to reduce the risk of transmission of the virus from the mother. to the child (read the Bufala).

The law n.135 of 1990 expressly provides that the test for the detection of anti-HIV antibodies is always carried out in compliance with the guarantees of confidentiality and confidentiality of health data. Legislative decree no. 124 of 29 April 1998, also referred to in the agreement between the state, regions and autonomous provinces of 27 July 2011, in art. 5, point b, underlines the gratuitousness of the test for the detection of anti-HIV antibodies.

The test can be performed in hospitals or in the laboratories of diagnostic centers, public or private, which are authorized to perform it. Before undergoing and at the time of delivery of the result, an informative interview (counseling) should be carried out on the methods of transmission and on the possibility of ascertaining HIV infection and sexually transmitted infections (STIs) by healthcare personnel properly trained.

For more and more in-depth information, as well as to find out if, when and where to carry out the test, you can contact your doctor or the AIDS and IST toll-free telephone of the Istituto Superiore di Sanità / Ministry of Health, the AIDS Network Services. , the United Against AIDS site and, more generally, the information services of public structures and non-governmental organizations.

The structures where to take the HIV test in Italy are listed on the Uniti contro l "AIDS site.

The test

Tests for HIV are able to highlight the presence of the virus or antibodies directed against it. To ascertain (diagnose) HIV infection, the first test to be performed is the search for specific antibodies in the blood by means of kits. authorized and valid for all types and subtypes of HIV. The methods mainly used are defined ELISA, EIA, ELFA or chemiluminescence and only recognize antibodies (test of third generation) or antibodies together with the p24 antigen (combined tests of fourth generation).

HIV antibodies appear in the blood over a period of 3 weeks to 3 months (window period) after the infection and it is therefore possible to carry out a test starting about a month after the behavior or event at risk.The test result, however, to be considered definitive, must be confirmed after 3 months, in the third generation tests, while, according to the indications of the Ministry of Health, the fourth generation tests, which are more sensitive and also recognize the " p24 viral antigen, can provide a definitive result starting 40 days after the risk event. It must be taken into account that in the window period the infection can be transmitted and therefore, before the final result of the test, it is necessary to protect any sexual intercourse with a condom.

Any positivity to the ELISA test must be absolutely confirmed by the named test western blot. More specific than the previous one, this test allows to highlight, on a nitrocellulose support, the presence of antibodies against individual HIV antigens. It requires higher costs and times than the traditional test and must be carried out by personnel adequately trained for its execution and for reading the results.

Rapid tests are currently available for the detection of anti-HIV antibodies that can be performed on the blood (a drop is enough) or on the saliva (gum secretion).

Rapid blood tests have a sensitivity comparable to that of traditional tests, while those on saliva, which may be influenced by individual factors or by the intake of food and drink, should be confirmed by a blood test. Apart from a rapid blood test. blood that can be purchased at pharmacies, rapid tests are usually performed at medical clinics in the presence of qualified personnel or in the context of awareness-raising initiatives in the area.

There are also tests for measuring the amount of virus in the blood (viral load or viremia) based on the molecular technique of gene amplification (real time PCR).Extremely sensitive, these tests are able to identify the presence of the viral genetic material and are mainly used to follow the progress of the infection over time in people in whom it has already been ascertained (diagnosed) and to adequately manage any treatment (therapy) anti-retroviral.

The viral load is in fact an index of the level of reproduction (replication) of the virus and, when the treatment is effective, the viral load drops below the value that can be measured by the method used. This means that the virus is kept under control by the therapy, preventing damage to the body's defense system (immune system). The evidence of non-measurable viral load, however, does not indicate that the infection has been eliminated since in the people being treated, the virus continues to reproduce, but at much lower levels, in the body's lymphatic tissue.

Results

The tests of third and fourth generation for the detection of HIV antibodies and p24 antigen (ELISA, EIA, ELFA) they are extremely sensitive and specific and have extremely low probability of error. The test is considered negative when the value found is below that measurable with the method and therefore, the presence of antibodies or p24 antigen in the blood can be excluded.

If, on the other hand, the result is clearly above this level, the test is considered positive and indicates, with a good level of certainty, the presence of anti-HIV antibodies or p24 antigen.

When the numerical value is around the measurable level, without being clearly above or below, the test should be repeated or the alternative western blot test should be performed.Any positive ELISA test, however, must always be confirmed by the western blot test so that HIV infection can be considered as ascertained (diagnosed) and the result can be communicated to the person concerned.

The western blot test highlights the presence of antibodies against individual viral antigens with a characteristic profile that allows to confirm the presence of the infection.

There are cases, however, in which even with a positive result of the ELISA test, the western blot test does not show with certainty the presence of antibodies against HIV, giving an indeterminate result. These circumstances may be due, in very rare cases , to a methodological anomaly of the ELISA test or, more likely, to very low levels of antibodies against HIV as occurs, for example, in the case of a very recent infection. In these cases it is not possible to establish with certainty whether HIV infection is present and, therefore, it is necessary to undergo another blood sample at a later time.

The test for measuring the viral load (real time PCR) is extremely sensitive and can detect the presence of the virus in the blood, confirming the positivity of the other tests for HIV. Generally, it is used to check the progress of the infection and the efficacy of antiretroviral treatment in people with HIV.

There are cases in which the viral load is not detectable in the blood even in the presence of anti-HIV antibodies, a phenomenon that occurs when the virus reproduces (replicates) at low levels only in the lymphatic tissue because it is adequately controlled by the defense system of the organism (immune system) or treatment.

For this reason, the PCR test cannot be considered on its own as a test capable of ascertaining (diagnosing) HIV infection and must always be performed in conjunction with the ELISA test.

Bibliography

UNAIDS. Global AIDS update 2016

Luzi AM, Colucci A, Suligoi B. (Ed.).The Italian legislation on HIV, AIDS and Sexually Transmitted Infections (STI). Rome: Higher Institute of Health; 2012. (ISTISAN reports 12/8)

Colucci A, Luzi AM, Gallo P, D'Amato S and Pompa MG (Ed.). Access to HIV testing: results of a research project by the Ministry of Health carried out by the Higher Institute of Health and by the Associations of the Council for the Fight against AIDS. Rome: Higher Institute of Health; 2011. (ISTISAN Reports 11/41)

Buttò S, Luzi AM, Pompa MG, Rezza G and Suligoi B. Laboratory diagnosis of HIV infection and access to HIV testing in Italy. Annals of the "Istituto Superiore di Sanità", 2010; 46

Di Sarno V, Botta F, Lichtner E, Colucci A, Gallo P, Luzi AM. HIV / AIDS cross-cultural telephone counseling. Rome: Higher Institute of Health; 2010. (ISTISAN reports 10/30)

Colucci A, Gallo P, Luzi AM (Ed.). The prevention of HIV infection: some experiences of telephone counseling in Italy. Rome: Higher Institute of Health; 2010. (ISTISAN reports 10/47)

Dalla Torre R, Taglieri FM, Gallo P, Colucci A, D "Agostini A, Fanales Belasio E, Lichtner E, Mulieri I, Schwarz M, Valdarchi C, Luzi AM. United against AIDS: the web as a prevention tool for sexually transmitted infections. News bulletin Higher Institute of Health. 2014; 27: 15-18

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