Human immunodeficiency virus, or HIV, is a virus that attacks the immune system. This makes it hard for the body to fight infection and disease. HIV is the virus that causes AIDS (acquired immunodeficiency syndrome). But having HIV doesn't mean that you have AIDS.

HIV often causes flu-like symptoms soon after a person gets infected. These early symptoms go away in a few weeks. After that, signs of illness may not appear for many years. But as the virus multiplies in the body, symptoms reappear and then remain. Fatigue, weight loss, fever, night sweats, diarrhea, and other symptoms are common.

Treatment of HIV may prevent or delay HIV from developing into AIDS. If HIV isn't treated and progresses to AIDS, symptoms get worse and the body is less and less able to fight infections like pneumonia and tuberculosis.

Medicines are the main treatment for HIV. A doctor would likely prescribe several antiretroviral medicines, sometimes called antiretroviral therapy, or ART. By fighting the virus, these medicines can help the immune system stay healthy and delay or prevent AIDS. And they may help a person live longer.

An HIV test checks for HIV antibodies in the blood. If HIV antibodies are found, the test is considered positive.

Most doctors use two blood tests, called the ELISA and the Western blot assay. If the first ELISA is positive (meaning that HIV antibodies are found), the blood sample is tested again. If the second test is positive, the doctor will do a Western blot to be sure.

Most test facilities will have the ELISA test results in 2 to 4 days. Results of the Western blot take longer, 1 to 2 weeks. Rapid antibody tests are available that give results right away. But positive results of the rapid test need to be confirmed by the ELISA or Western blot test.

Even if HIV antibodies aren't found, you may need to be tested again, especially if you think you have been exposed. This is done to make sure that HIV antibodies don't appear at a later time. It can take as little as 2 weeks or as long as 6 months from the time you become infected with HIV for the antibodies to be found in your blood. Tests given at 6, 12, and 24 weeks can be done to be sure you aren't infected.

During this period, an infected person can still spread the infection even though his or her test was negative.

You can get HIV testing in most doctors' offices, public health clinics, hospitals, and Planned Parenthood clinics. You can also buy a home HIV test kit (saliva test) in a drugstore or by mail order. But be very careful to choose only a test that has been approved by the U.S. Food and Drug Administration (FDA). If a home test is positive, you'll need to see a doctor to have the result confirmed and to find out what to do next.

Experts don't fully agree on who should be tested for HIV:

The U.S. Centers for Disease Control and Prevention (CDC) recommends that all people should get tested for HIV as part of their regular medical care.

The U.S. Preventive Services Task Force (USPSTF) recommends HIV tests for all adults and adolescents who have a high risk for HIV. The agency recommends screening if:

• You or your sex partner(s) engages in high-risk behavior.
• You're pregnant.
• You've been to a sexually transmitted infection (STI) clinic or a tuberculosis (TB) clinic.

High-risk behavior means that you:

• Are a man who has sex with other men.
• Have multiple sex partners, especially partners who inject drugs.
• Inject drugs or steroids, especially if you share needles, syringes, cookers, or other equipment used to inject drugs.
• Have high-risk partner(s) (a man or woman who has multiple sex partners or injects drugs, or a man who has sex with men).
• Have or have recently had a sexually transmitted infection, such as syphilis or genital herpes.

Some expert opinions may vary, and your doctor may recommend testing based on your personal history.

Even if you don't think you're at risk, it's worthwhile getting tested once. In some cases people who've had a positive test didn't believe they had a high risk before having the test.

Getting tested can help find an infection early or when you have no symptoms. This is important so that:

• You can take steps to avoid spreading the infection.
• You can tell your sex partner(s) so they can be tested, get treatment if needed, and avoid spreading the infection.
• You can start treatment right away or as soon as needed. Treatment can help your immune system stay healthy and delay or prevent AIDS. And it may help you live longer. AIDS is the last and most severe stage of HIV infection. Treatment also lowers the chance that you will give the infection to a sex partner who doesn't have the infection.²
• If you are pregnant, you can get early treatment that can reduce the risk of passing HIV to your baby.

If your test shows that you have HIV, your sex partner(s) will need to know and get tested, which may affect your relationship.

If you have HIV, state law may require your doctor or the place where you had the test to report it to the state health department. Some states allow anonymous reporting (the person's name or other identifying information is not provided). Other states require confidential reporting (identifying information is provided but only to authorized public health officials).

With an ELISA test, you could have a false-positive test result, which shows that you have the disease when you actually don't. This could cause you unneeded worry until you have more tests to confirm that you don't have the disease.

If you use a home test kit, you could get a fast result, but it will still need to be confirmed with a test that can take several weeks.

Your doctor may want you to be tested if:

• You're sexually active.
• You have never had an HIV test.
• You have a high risk for getting HIV.
• You're pregnant.