For basic questions and answers about HIV testing, visit our HIV testing basics page.
At the end of 2009, an estimated 1,148,200 persons aged 13 and older were living with HIV infection in the United States, including 207,600 (18.1%) persons whose infections had not been diagnosed. CDC estimates that approximately 50,000 people are infected with HIV each year (1 2).
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.
Rationale for Routine Screening for HIV Infection
People who are infected with HIV but not aware of it are not able to take advantage of the therapies that can keep them healthy and extend their lives, nor do they have the knowledge to protect their sex or drug-use partners from becoming infected. Knowing whether one is positive or negative for HIV confers great benefits in healthy decision making. Cohort studies have demonstrated that many infected persons decrease behaviors that help transmit infection to sex or needle-sharing partners once they are aware of their positive HIV status (3-10). HIV-infected persons who are unaware of their infection do not reduce risk behaviors (11,12,13). Persons tested for HIV who do not return for test results might even increase their risk for transmitting HIV to partners (14). Because medical treatment that lowers HIV viral load might also reduce risk for transmission to others (15), early referral to medical care could prevent HIV transmission in communities while reducing a person's risk for HIV-related illness and death.
HIV Testing Technologies
The most common HIV test is the antibody screening test, which tests for the antibodies that your body makes against HIV, not HIV itself. Antibody tests may be conducted in a lab or as a rapid test at the testing site. They may be performed on blood or oral fluid (not saliva).
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 fluid. In addition, most blood-based lab tests find infection sooner after exposure than rapid HIV tests. Newer blood tests can find HIV as soon as 3 weeks after exposure to the virus.
In addition to antibody tests, there are several tests now in use that can detect both antibodies and antigens, which are pieces of the virus itself. Because these tests do not have to wait for the body to make an immune response to the virus, they can find infection earlier than tests that only look for antibodies.
Follow-up diagnostic testing is performed if the first 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 first test is a rapid test, and it is positive, you will be directed to a medical setting to get follow-up testing. If your first test that required a lab for analysis is positive, the lab will conduct follow-up testing, usually on the same blood specimen as the first test.
Follow-up tests include:
- an antibody differentiation test, which distinguishes HIV-1 from HIV-2;
- a Western blot or indirect immunofluorescence assay, which detect antibodies
- an HIV-1 nucleic acid test, which looks for virus directly.
If you would like to learn more about HIV tests that are FDA-approved for use in the United States please go to US HIV tests and Algorithms.
CDC is drafting revised laboratory HIV diagnostic guidelines due to evidence that many persons infected with HIV at the time of testing are not detected by current testing strategies. The proposed testing process recommends
- Initial screening with a sensitive HIV antigen/antibody test.
- If reactive, the initial test is followed by a differentiation test that distinguishes HIV-1 from HIV-2.
- If the differentiation test is negative or indeterminate, HIV-1 nucleic acid testing, which looks specifically for components of HIV, is performed to identify new infections.