Tests for HIV Diagnosis

If you're worried that you might have been exposed to human immunodeficiency virus (HIV) -- the virus that causes AIDS -- it's important to get tested as soon as possible. Although the prospect of being diagnosed with the disease can be scary, today you can live a long and full life with HIV, especially if you start treatment early. Knowing you are infected can also help you take precautions so that you don't pass the virus to other people.

Several different tests are used to diagnose HIV infection. Other tests are used to select and monitor treatments in people who are living with HIV.

If you are infected with the HIV virus, your body will start to produce infection-fighting proteins against the virus, called antibodies. HIV antibody tests look for these proteins in your blood or other body fluids.

The most common HIV test, the enzyme-linked immunosorbent assay, or ELISA (also called EIA), is used to detect HIV antibodies in a sample of your blood. The device for test is microplate reader. Other versions of the antibody HIV test use a sample of saliva or urine.

Although HIV tests are very sensitive, they can produce false-positive results. So ELISA HIV tests must be confirmed with another HIV test, such as a Western blot or indirect immunofluorescence assay (IFA).

Antibodies won't show up in your blood or body fluid immediately after you've been infected. There is a "window period" of six to 12 weeks, and sometimes several months, before your body starts producing antibodies to the virus. So even if you tested negative within a few weeks of being exposed to HIV, you should get tested again at three months and six months.

Important note: The HIV virus is transmissible during the window period, even though the test may come back as negative.