Diagnosis of HIV infection
HIV testing is used for early diagnosis. Methods for diagnosing infection are constantly being improved, since the main symptoms of the disease do not appear immediately, disguising themselves as other pathologies. In addition, in laboratory tests, there is a high percentage of both false positive and false negative results.
Test systems use blood to determine HIV, less often urine and scrapings from the oral mucosa are used for this.
Stages of diagnosis of HIV infection in adults:
- Preliminary - screening, selecting candidates at risk (presumably infected);
- Reference
- Confirmatory - expert stage.
The complexity, labor intensity and cost of research methods grow from stage to stage.
Terms used in HIV diagnosis:
- Antigen - HIV or parts of it (capsule, enzymes, lipids, proteins).
- Antibody - cells of the immune system produced by the body against the introduction of a viral infection.
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Seroconversion is the immune response of the defense system against the active multiplication of the virus. Immediately after entering the body, HIV cells begin to actively divide. In response, the concentration of antibodies rises for several weeks. Their achievement of a certain level (seroconversion) is available to test systems for diagnostics. After the concentration of the virus drops, the level of antibodies drops.
- "Window period" - the time interval from the moment of infection to the appearance of seroconversion, takes from 1.5 to 3 months. An infected person during this period is especially dangerous as a carrier of infection, since an HIV test shows a false negative result, although the risk of transmission of the disease is extremely high.
Screening stage of HIV diagnosis
During the screening, an enzyme-linked immunosorbent assay (ELISA) is carried out to determine the total antibodies to HIV-1 and HIV-2. Shows accurate results no earlier than 3-6 months after infection, although there are exceptions: it can detect antibodies to HIV 3-5 weeks after a dangerous contact.
Fourth generation test systems are the most accurate. In addition to antibodies to the virus, they are able to determine also the antigen to HIV (p-24-Capsid), which makes it possible to detect the virus even in the "window period", before the appearance of antibodies.
The high cost of such test systems forces many countries to use third and even second generation systems that determine only the presence of antibodies.
Such systems give false positive results under the following conditions:
- Infection during pregnancy;
- Autoimmune diseases: psoriasis, rheumatism, systemic lupus erythematosus;
- The presence of the Epstein-Bar virus.
If the result of the enzyme immunoassay is positive, they proceed to the next stage of diagnosis.
Reference stage of HIV diagnosis
A double diagnosis with more sensitive test systems is used. Two positive results are a reason to move to the next level of diagnostics.
Expert stage - immunoblotting
At this stage, antibodies to individual proteins of the human immunodeficiency virus are determined.
Expert stage stages:
- Breakdown of the virus into individual antigens using electrophoresis.
- Transfer of antigens using the method of blotting onto special strips with pre-applied proteins characteristic of HIV.
- Fixation of the reaction that occurs if there are antibodies to antigens in the patient's blood.
There is a small risk of bias - a false negative result. It is possible if the study takes place in the terminal stage of the disease or in the "window period".
In combination with other tests, the PCR method (polymerase chain reaction) is used. It is highly susceptible to the virus, which can lead to a high rate of false positives.
Diagnosis in children whose mothers are HIV-infected
The testing of such children has its own characteristics - the mother's antibodies to HIV, which have penetrated the placenta during childbirth, may be present in the child's blood. They can last up to 15-18 months from the birth of the baby. if there are no such antibodies, this is not one hundred percent proof that the child is not infected with the virus.
Diagnostic tactics in children born to HIV-infected mothers:
- In the first month of life - PCR, since during this period the virus does not actively multiply;
- Over a month - a test to determine the p-23-Capsid antigen;
- Diagnostic measures up to 36 months of life.
Author of the article: Alekseeva Maria Yurievna | Therapist
Education: From 2010 to 2016 Practitioner of the therapeutic hospital of the central medical-sanitary unit No. 21, city of elektrostal. Since 2016 she has been working in the diagnostic center No. 3.
