HIV Testing

Background

An estimated 1.1 million people in the United States are living with HIV, including about 166,000 people who are unaware of their status. Thirty percent of new HIV infections are transmitted by people who are living with undiagnosed HIV. For those who are living with undiagnosed HIV, testing is the first step in maintaining a healthy life and reducing the spread of HIV.

CDC’s Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings advises routine HIV screening of adults, adolescents, and pregnant women in health care settings in the United States. The recommendations also call for reducing barriers to HIV testing. In April 2013, the U.S. Preventive Services Task Force issued similar recommendations.

CDC recommends that everyone between the ages of 13 and 64 get tested for HIV at least once as part of routine health care. For those with specific risk factors, CDC recommends getting tested once a year.

Data from a clinical trial sponsored by the National Institutes of Health shows a clear personal health advantage to being diagnosed with HIV early and starting therapy right away. This information further highlights the importance of routine HIV testing and its potential impact on better health outcomes.

Importance of HIV Testing for Prevention of HIV Infection

People with HIV who are aware of their status can get HIV treatment (antiretroviral therapy, or ART) and remain healthy for many years. Studies show that the sooner people start treatment after diagnosis, the more they benefit from ART. Treatment with ART lowers the level of HIV in the blood (viral load), reduces HIV-related illness, and lowers the risk of transmitting HIV to others. Taking ART the right way every day can reduce a person’s chance of transmitting HIV through sex by as much as 96%.

People who get tested and learn they are HIV-negative can also make decisions about sex, drug use, and health care that can protect them from HIV. For people at very high risk for HIV, taking daily HIV medicine called pre-exposure prophylaxis or PrEP can prevent HIV infection by more than 90%.

HIV Tests for Screening and Diagnosis

HIV tests are very accurate, but no test can detect the virus immediately after infection. How soon a test can detect infection depends upon different factors, including the type of test being used. There are three types of HIV diagnostic tests: nucleic acid tests (NAT), antigen/antibody tests, and antibody tests.

• NATs look for the actual virus in the blood. This test is very expensive and is not routinely used for HIV screening unless the person recently had a high-risk exposure or a possible exposure with early symptoms of HIV infection.
• Antigen/antibody tests look for both HIV antibodies and antigens. Antigens are foreign substances that cause your immune system to activate. If you’re infected with HIV, an antigen called p24 is produced even before antibodies develop. Tests that detect both antigen and antibodies are recommended for testing done in labs and are now common in the United States. There is also a rapid antigen/antibody test available.
• Antibody tests detect the presence of antibodies, proteins that a person’s body makes against HIV, not HIV itself. Most rapid tests and home tests are antibody tests.

An initial HIV test usually will either be an antigen/antibody test or an antibody test. If the initial HIV test is a rapid test and it is positive, the individual will be sent to a health care provider to get follow-up testing. If the initial HIV test is a laboratory test and it is positive, the laboratory will usually conduct follow-up testing on the same blood sample as the initial test. Although HIV tests are generally very accurate, follow-up testing allows the health care provider to be sure the diagnosis is right.

Resources for FDA-approved laboratory tests and home tests are available. Learn more about testing in nonclinical settings and testing in clinical settings.

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