An estimated 1.2 million people in the United States have HIV, including about 158,500 people who are unaware of their status. Nearly 40% of new HIV infections are transmitted by people who don’t know they have the virus. For people with undiagnosed HIV, testing is the first step in maintaining a healthy life and preventing HIV transmission.
For information about HIV: how's it's transmitted, how you can prevent it, and how to get tested, visit CDC HIV Basics
HIV Testing at CCRI
Importance of HIV Testing for Prevention of HIV Infection
People with HIV who know their status can get HIV treatment (called antiretroviral therapy or ART) and remain healthy for many years. Studies show that the sooner people start HIV treatment after diagnosis, the more they benefit. HIV treatment reduces the amount of HIV in the blood (called viral load), reduces HIV-related illness, and prevents transmission to others. People with HIV who take HIV treatment as prescribed and get and keep an undetectable viral load (or stay virally suppressed) will not transmit HIV to their sex partners.
People who get tested and learn they don’t have HIV can make decisions about sex, drug use, and health care that can help prevent prevent HIV. Taking HIV medicine called pre-exposure prophylaxis (PrEP) is highly effective for preventing HIV.
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 HIV depends on the type of test being used. There are three types of HIV tests: antibody tests, antigen/antibody tests, and nucleic acid tests (NAT).
- Antibody tests look for antibodies to HIV in a person’s blood or oral fluid. Antibody testscan take 23 to 90 days to detect HIV after exposure. Most rapid tests and the only FDA-approved HIV self-test are antibody tests. In general, antibody tests that use blood from a vein can detect HIV sooner after infection than tests done with blood from a finger stick or with oral fluid.
- Antigen/antibody tests look for both HIV antibodies and antigens. Antibodies are produced by a person’s immune system when they’re exposed to viruses like HIV. Antigens are foreign substances that cause a person’s immune system to activate. If a person has HIV, an antigen called p24 is produced before antibodies develop. Antigen/antibody tests are recommended for testing done in labs and are common in the United States. An antigen/antibody test performed by a lab on blood from a vein can usually detect HIV 18 to 45 days after exposure. There is also a rapid antigen/antibody test available that is done with a finger stick. Antigen/antibody tests done with blood from a finger stick can take 18 to 90 days after exposure.
- NATs look for the actual virus in the blood. This test should be considered for people who have had a recent exposure or a possible exposure with early symptoms of HIV and have tested negative with an antibody or antigen/antibody test. A NAT can usually detect HIV 10 to 33 days after exposure.
An initial HIV test usually will either be an antigen/antibody test or an antibody test. If the initial HIV test is a rapid or self-test and it is positive, the person should go to a health care provider to get follow-up testing. If the initial HIV test is a lab test and it is positive, the lab will usually conduct follow-up testing on the same blood sample as the initial test. Although HIV tests are generally accurate, follow-up tests allow the health care provider to confirm the result.