The safest way to get tested is in the institutions and organizations that conduct counseling and testing programs. If, for any reason, you do it privately, on your own initiative, you will come across various tests: preliminary, confirmatory and those used during the treatment of HIV infection.
Prepared by: Bratislav Prokić, October 2022
Review: Prof. Dr. Biljana Kocić, epidemiologist,
Institute of Public Health - Niš
What are preliminary tests for HIV?
Elisa and rapid tests are most often used to detect HIV infection. Although we call them preliminary, they are very reliable. The most important thing is to respect the window period,which is the time from the moment when you may have been exposed to the virus, until the moment when a test can definitely detect it.
What is the window period for HIV tests?
The test, which uses venous blood,can reliably confirm or exclude the presence of HIV infection as early as 6 weeks after potential exposure to the virus. It is an ELISA (or EIA) of the fourth generation, and it is also called “HIV Combo ag/ab”, because it detects both a part of the virus (antigen) and a specific part of the immune response to the presence of infection (antibodies).
The test, which uses a drop of blood from a finger (capillary blood), can reliably confirm or exclude the presence of HIV infection, after 3 months of potential exposure to the virus. It is a rapid test that detects the presence of antibodies to HIV, which the body creates in response to infection.
The test that detects HIV from saliva “OraQuick” has a window period of 3 months as well as the rapid test. These tests have not been registered in Serbia at the time of writing.
Which test can detect HIV the earliest?
The PCR test directly looks for HIV in the blood and therefore can detect early infection, before the formation of antibodies, already after 10 days. The PCR method is not recommended for testing (screening) for HIV, except in special circumstances.
What are HIV confirmatory tests and when are they used?
A positive (reactive) result of a preliminary HIV test must be confirmed by a PCR test, and a Western blot is also used to establish the diagnosis.
The PCR HIV RNA Western blot
Western blot detects antibodies to several specific HIV proteins (gp120, gp41, p24, p17, p31, gp36, sgp105, sgp120), and is reliable after three months of infection.
If enough time has passed from the risk you had to the test (window period) and the result of the HIV test is negative, you do not need to repeat the test, nor do confirmatory tests.
How reliable are the tests?
The accuracy of a test, in addition to the expertise of the person performing the test, depends primarily on characteristics known as sensitivity and specificity. Many modern HIV tests are extremely sensitive (over 99%) and extremely specific (over 99%).
What does the sensitivity and specificity of an HIV test mean?
Test sensitivity is the percentage of correct positive results when HIV is actually present, and specificity is the percentage of correct negative results when HIV is not present. Lower sensitivity rates will produce more false negatives, and lower specificity rates will produce more false positives.
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