People exposed to the virus should get an HIV test as soon as they are likely to develop antibodies to the virus - within 6 weeks to 12 months after possible exposure to the virus. By getting tested early, people with HIV infection can discuss with a health care provider when they should start treatment to help their immune systems combat HIV and help prevent the emergence of certain opportunistic infections (see section on treatment below). Early testing also alerts HIV-infected people to avoid high-risk behaviors that could spread the virus to others.

Most health care providers can do HIV testing and will usually offer counseling to the patient at the same time. Of course, individuals can be tested anonymously at many sites if they are concerned about confidentiality.

Health care providers diagnose HIV infection by using two different types of antibody tests, ELISA and Western Blot. If a person is highly likely to be infected with HIV and yet both tests are negative, the health care provider may request additional tests. The person also may be told to repeat antibody testing at a later date, when antibodies to HIV are more likely to have developed.

Babies born to mothers infected with HIV may or may not be infected with the virus, but all carry their mothers' antibodies to HIV for several months. If these babies lack symptoms, a doctor cannot make a definitive diagnosis of HIV infection using standard antibody tests until after 15 months of age. By then, babies are unlikely to still carry their mothers' antibodies and will have produced their own, if they are infected. Health care experts are using new technologies to detect HIV itself to more accurately determine HIV infection in infants between ages 3 months and 15 months. They are evaluating a number of blood tests to determine if they can diagnose HIV infection in babies younger than 3 months.

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