What tests are used to diagnose and monitor HIV?

There are several types of tests associated with HIV disease. Some test for antibodies that the body makes in response to the virus, some test for levels of a protein (called p24) found in the virus, some test for the actual number of copies of the virus per milliliter of blood (called viral load testing), some test for levels of immune cells called CD4 cells that are attacked by HIV, and some test for whether patients are resistant to anti-HIV drugs.

• Antibody testing—to diagnose HIV infection.
• p24 protein testing—may be used to detect early HIV infection, to monitor HIV therapy and HIV progression, and to screen blood for HIV.
• Viral load testing—to decide when to start therapy and to monitor therapy and HIV progression.
• CD4 testing—to decide when to start therapy and to monitor therapy, HIV progression, and the status of the immune system.
• Genotypic resistance testing—to determine if a particular strain of HIV is resistant to the therapy you are on and if the therapy should be switched.

When are these tests ordered?

One or more of these tests are ordered after a person is exposed to HIV and decides to be tested, either at the doctor’s office or a local clinic. Some approved home-test kits allow you to take a blood sample from your finger, send it to a lab, and receive your results later over the phone along with counseling. These are not tests that can be performed at home. Several of the tests listed above are then ordered at intervals by a doctor to monitor the course of therapy.