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Background

For basic questions and answers about HIV testing, visit our HIV testing basics page.

At the end of 2010, an estimated 1,144,500 persons aged 13 and older were living with HIV infection in the United States, including 180,900 (15.8%) persons whose infections had not been diagnosed1. The estimated incidence of HIV has remained stable overall in recent years, at about 50,000 new HIV infections per year2.

HIV testing is entering a new era in this country as lawmakers, health care and insurance executives, and public health officials are making changes in their respective fields to ensure that more people will know their HIV status – an important consideration for maintaining health and reducing the spread of the virus. In September 2006, CDC released Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings. These Recommendations advise routine HIV screening of adults, adolescents, and pregnant women in health care settings in the United States. They also recommend reducing barriers to HIV testing.

In April 2013, the U.S. Preventive Services Task Force (USPSTF) recommended that clinicians screen adolescents and adults ages 15 to 65 years for HIV infection. Younger adolescents and older adults who are at increased risk should also be screened. They also recommend screening all pregnant women for HIV, including those who present in labor whose HIV status is unknown.

Importance of HIV Testing for Prevention and Treatment of HIV Infection

People with HIV who know they are infected can get treatment (antiretroviral medications).  Effective treatment keeps HIV infected people healthy and living longer. Studies indicate that all people with HIV infection, including those with early infection, benefit from antiretroviral medications3. Treatment with antiretroviral medications lowers the level of HIV in the blood (viral load), reduces HIV-related illness, and reduces the spread of HIV to others4

Knowing they have HIV infection allows people with HIV to protect other people with whom they have sex or share drugs and needles from becoming infected. Knowing that one is positive for HIV helps that person to make better decisions about sex and health care. Studies have shown that many people with HIV who know that they are infected avoid behaviors that spread infection to others with whom they have sex or share drugs and needles5-12. HIV-infected persons who do not know that they are infected do not avoid unsafe behaviors13,14,15.  Persons who know they have HIV can get medical care and take antiviral medications that can reduce HIV spread by as much as 96%4.    

Knowing that one does not have HIV infection can also help that person make better decisions about sex, drug use, and health care. For example, antiretroviral medications can also be used to prevent HIV infection in persons who are HIV-negative. This is called pre-exposure prophylaxis or PrEP. Doctors planning to prescribe PrEP must conduct testing to ensure that patients are HIV-negative before they start PrEP.

HIV Tests For Screening and Diagnosis

There are three types of HIV diagnostic tests: antibody tests, antigen/antibody tests, and nucleic acid (RNA) tests.  Antibody tests detect antibodies, proteins that your body makes against HIV, not HIV itself. Antigen tests and RNA tests detect HIV directly.

An initial HIV test will either be an antibody test or antigen/antibody test. It may involve sending blood or oral fluid to a laboratory or obtaining blood or oral fluid for a rapid test. Blood tests can detect HIV infection sooner after exposure than oral fluid tests because the level of antibody in blood is higher than it is in oral fluid1. Likewise, antigen/antibody and RNA tests detect infection in blood before antibody tests2.Some newer antigen/antibody lab tests can sometimes find HIV as soon as 3 weeks after exposure to the virus.  No antigen/antibody or RNA tests are available for oral fluid. 

Follow-up testing is performed if the initial test result is positive. HIV tests are generally very accurate, but follow-up testing allows you and your health care provider to be sure the diagnosis is right. If your initial test is a rapid test and it is positive, you will be directed to get follow-up testing. If your initial test is a laboratory test and it is positive, the laboratory will usually conduct follow-up testing on the same blood specimen as the initial test.
Follow-up tests include:

  • antibody differentiation tests, which distinguishes HIV-1 from HIV-2 antibodies;
  • HIV-1 nucleic acid tests, which looks for the virus RNA directly;
  • Western blot and indirect immunofluorescence assay, which detect antibodies.

CDC has issued revised recommendations for laboratory testing for the diagnosis of HIV infection because of evidence that many persons infected with HIV at the time of testing were not detected by some antibody tests or the Western blot.
If you would like to learn more about HIV tests that are FDA-approved for use in the United States please go to U.S. HIV tests

References:

1. Luo W, Masciotra S, Delaney KP, Charurat M, Croxton T, Constantine N, et al. Comparison of HIV oral fluid and plasma antibody results during early infection in a longitudinal Nigerian cohort. J Clin Virol, 2013. 58 Suppl 1: e113-8.
2. Masciotra S, Luo W, Youngpairoj AS, Kennedy MS, Wells S, Ambrose K, et al. Performance of the Alere Determine HIV-1/2 Ag/Ab Combo Rapid Test with specimens from HIV-1 seroconverters from the US and HIV-2 infected individuals from Ivory Coast. J Clin Virol, 2013.

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