HIV

Overview
Testing
Prevention & Treatment
Common Questions
Sources

Tests

Laboratory Tests

Testing associated with HIV/AIDS involves either measuring the affected patient’s response to HIV (antibodies) or measuring and evaluating the virus itself. Most tests are performed using the patient’s blood. The goals of HIV testing are to:

screen for and diagnose HIV infection – confidential or anonymous testing is available for those who think they may have been exposed. Initial tests often involve testing a small sample of blood from a fingerstick or oral fluid (saliva) for HIV antibodies produced by the patient’s immune system. Results are often available within minutes; however, a positive screening result needs to be confirmed by another test.
measure and monitor the amount of virus in the patient’s blood (the viral load)
evaluate and monitor the patient’s immune function status
evaluate HIV’s resistance to available drug therapies

Specific tests may include:

HIV antibody testing—ordered to diagnose HIV infection.
p24 protein testing—may be used to detect early HIV infection and to screen blood products for HIV.
HIV viral load testing—measures the quantity of HIV virus in the blood. Ordered to help decide when to start therapy and ordered at intervals to monitor the effectiveness of therapy.
CD4 count—measures the number of CD4 T-cells in the blood. Ordered at intervals to determine when to start HIV therapy. Also ordered to monitor therapy, HIV progression, and the status of the immune system.
HIV genotypic resistance testing—ordered to determine whether the particular strain(s) of HIV that the patient has are resistant to available antiretroviral drug therapies. Ordered when a patient is initially diagnosed to determine whether, and to which drugs, the HIV is resistant. Also ordered when treatment is initiated, changed, and when there is evidence of treatment failure.
Phenotypic resistance testing–sometimes ordered on patients who are resistant to multiple antiretroviral drugs to help guide treatment. This test evaluates whether the patient’s strain(s) of HIV can grow in various concentrations of antiretroviral drugs.

Other laboratory testing may be performed to identify and monitor the treatment of opportunistic infections, complications, and drug toxicities. Testing may also be ordered at intervals to evaluate the patient’s state of health and organ function. Some tests are ordered to evaluate risks associated with using a specific HIV treatment. For instance, the drug abacavir can cause a potentially severe hypersensitivity reaction in some patients. Those who are planning to take the drug may be tested first for the gene allele, HLA-B*5701. If they are positive for it, they are at an increased risk of having a reaction and another drug should be considered.

Non-Laboratory Tests
Testing such as a chest x-ray or an imaging scan may sometimes be performed to help evaluate the patient’s health status.