How Is HIV/AIDS Diagnosed?

How Is HIV/AIDS Diagnosed?

In order to diagnose HIV infection, doctors perform a blood test to look for antibodies ^* to the virus. This test may not show signs of infection until several months after infection occurs. Other tests can detect the presence of the virus in the blood directly. The most common of these uses a technique called the polymerase (pah-LIM-er-ace) chain reaction (PCR). Special cultures ^* of the blood for HIV or a measurement of p24 antigen (AN-tih-jen), a part of the virus's coat, are available but are used less frequently.

A diagnosis of AIDS is made when a person who is infected with HIV develops certain infections or conditions associated with the disease that indicate a weakening of the immune system. AIDS is also diagnosed when the number of CD4+ T-cells in the body drops below a certain level. The level or "count" of these cells can be measured by taking a blood sample.