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An HIV test shows if someone is infected with HIV, the virus that attacks the body’s immune system and causes acquired immune deficiency syndrome, or what is more commonly known as AIDS. There are several different tests that can be used to determine if you are carrying the HIV virus.
The first test developed is still the most frequently used for the initial detection of HIV infection: the enzyme-linked immunosorbent assay or as it’s more commonly known, the ELISA.
The ELISA is usually done by drawing blood, usually from a vein in the arm. If the ELISA test is negative – meaning that antibodies are not found – the testing is complete.
If the ELISA test is positive, the laboratory will want to make sure that it is not a “false positive” result (some molecules in the bloodstream can sometimes cause a false-positive result, such as with an infant who was exposed to HIV via his mother).
First, they may repeat the ELISA test. If it’s positive, they will conduct a test called Western blot. If both the ELISA and the Western blot test yield a positive result, a diagnosis of HIV infection is confirmed and the results are sent back to the healthcare professional who ordered the test.
Quantitative Polymerase Chain Reaction (PCR): The quantitative PCR, also known as the viral load test, is a test frequently used in Ethiopia for infants. It is considered to be highly reliable for someone who may have recently been exposed to the virus, such as an infant whose mother is HIV positive. If the virus is present, the quantitative PCR will reveal how much virus is in a person’s bloodstream (the viral load).
In most cases, a quantitative PCR is highly accurate within 48 to 72 hours. However, a small number of people don’t have viral loads that are high enough to confirm a diagnosis until 28 days after exposure. The standard recommendation is that a negative PCR result be confirmed with an ELISA test at 13 weeks.
This information was taken from the following website:
A Complete Guide to Testing for HIV
“false-positive result, such as with an infant who was exposed to HIV via his mother”
The infant actually carries the antibodies that the mother’s immune system created (passed through the placenta) and this causes the false-positive not direct “exposure to HIV via his mother”. In reality, it’s not really a false-positive since the ELISA tests for antibodies and the child has antibodies in his blood (it’s just that the antibodies aren’t due to him being infected with the virus). The mother’s antibodies can survive in the infant’s bloodstream for more than a year. True false-positives (where the child doesn’t have the antibody but is declared positive) are very rare. Unfortunately, false-negatives (HIV positive children who test negative) may be more common especially with the ELISA test due to the antibodies being degraded prior to the test being completed. My understanding is that the PCR test may have a lower rate of false-negatives because it’s more sensitive and DNA degrades slower than proteins (antibodies) but a quick Google search didn’t find any data on that.
Thanks, Brian, for clarifying this!!!
mary