How Is HIV Infection Diagnosed?

A blood test is used to confirm whether a person has been infected with HIV. Anyone who has engaged in risky behavior – such as sharing drug – injecting equipment or having unprotected sexual contact with an infected person or with someone whose HIV status is unknown – should consider being tested.

A positive HIV test result does not mean that a person has AIDS. Not everyone who has HIV infection develops AIDS. Experts estimate that about half the people with HIV will develop AIDS within 10 years after becoming infected.

Early diagnosis of HIV infection is important because:

  • It allows people to seek treatment that will help suppress HIV’s attack on the immune system and prevent opportunistic infections.
  • It helps women at risk for HIV infection who are planning a pregnancy or who are already pregnant take steps to reduce the risk of transmitting the infection to the baby.
  • It alerts those who are infected that they could infect others.

How To Information:

Where is HIV testing available?

HIV testing is available at most hospitals, family planning clinics, sexually transmitted disease (STD) clinics, community health centers, drug treatment facilities, and doctor’s offices. Individuals can contact their local health department for testing centers in their area. In many states, it is possible to be tested anonymously.

Information about testing centers is also available by calling the CDC’s National AIDS Hotline. (See Additional Sources Of Information.) Testing centers will also provide counseling about HIV and AIDS and help people understand their test results.

Nice To Know:

Q: Is a home test kit for HIV available?

A: No approved HIV test kit will give you a result at home. There is a kit available that is designed for you to collect a sample of your blood at home. Then you send the sample to a laboratory where it is tested for HIV.

What Kinds Of Blood Tests Are Used?

The blood tests most commonly used to diagnose HIV infection work by measuring the levels of antibodies produced by the body against HIV. Antibody-detecting assays, or tests, include the:

  • Enzyme immunoassay (EIA)
  • Enzyme-linked immunosorbent assay (ELISA)
  • Western blot test

Usually, the first test that laboratories use to detect the presence of HIV antibodies is an EIA or the ELISA. If the first test produces a positive result (HIV antibodies appear to be present), then the more sensitive Western Blot test is used to confirm it.

EIA or ELISA tests take from one to two weeks to complete, depending on where the test is performed.

Why Is It Often Necessary To Repeat An HIV Test?

Although a negative result on an HIV blood test usually means that the person is not infected with the virus, that is not always the case. The body may take three to six months after exposure to the virus to produce enough antibodies to be detectable in the bloodstream.

Because of this delay between infection and the appearance of HIV antibodies, a person should be retested six months after the last possible exposure to HIV. It is also important to remember that a person who has been exposed to HIV can pass the virus to others even before HIV antibodies appear in the bloodstream.


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