HIV antibody testing is used to screen for and diagnose HIV infections. Since there is no cure, early treatment of HIV infection and immune system monitoring can greatly improve long-term health and survival. Also, if a person knows his HIV status, it may help change behaviors that can put him and others at risk.
Different types of antibody tests may be used for HIV screening:
All HIV tests used in the U.S. detect HIV-1, and some tests have been developed that can also detect HIV-2. (HIV-1 is the most common type found in the United States, while HIV-2 has a higher prevalence in parts of Africa.)
Combination tests have been developed that detect HIV antibody and the HIV antigen called the p24 antigen. Levels of p24 antigen are typically high early in the course of infection. A combination test may be performed to increase the likelihood that HIV infection is detected sooner after exposure occurs.
Various options are available for getting tested:
A blood or oral sample can be collected in a doctor's office or a local clinic and sent to a laboratory for testing.
In these same settings, there may be a rapid test available in which results are generated in about 20 minutes.
There is also a home collection kit approved by the U.S. Food and Drug Administration (FDA) that is available for HIV antibody testing. This allows a person to take a sample at home and then mail it to a testing center. Results are available over the phone, along with appropriate counseling.
In July 2012, the FDA approved for marketing the first HIV test for home use. The testing kit is the same as that used in many doctors' offices and clinics in which an oral sample is collected for testing and results are available in about 20 minutes. The home test has two limitations: 1) testing on oral fluid is less sensitive than a blood test so the home test may miss some cases of HIV that a blood test would detect; and 2) the home test is not as accurate when it is performed at home by a lay person compared to when it is performed by a trained health care professional. However, the FDA felt that the convenience of home testing would encourage some people who might otherwise be reluctant to go to a doctor or clinic to learn their HIV status.
Regardless of the type of screening test used, a positive result requires follow up with a second test to establish a diagnosis of HIV. Current testing protocols usually involve an initial screening test that uses a method called an immunoassay (IA). If positive, the HIV antibody immunoassay test is repeated. It is a very sensitive type of test but currently requires a second test method, usually a Western blot, to confirm the results because false positives can occur.
With the aim of improving the diagnostic process, a new testing protocol has been proposed and is in the process of being implemented. Over time, more clinics and doctors may opt to follow these steps:
Screen for HIV using an HIV antigen/antibody test or an HIV antibody test, then:
Verify a positive with a second HIV antibody test that differentiates between HIV-1 and HIV-2
If results between the first and second test do not agree, then the next test to perform is a HIV-1 RNA test (nucleic acid amplification test, NAAT). If the HIV-1 RNA is positive, then the test is considered positive.
Several organizations recommend routine screening for HIV:
The Centers for Disease Control (CDC), American College of Physicians (ACP), and HIV Medicine Association (HMA) recommend that anyone between the ages of 13 and 64 be screened for HIV at least once.
The CDC and American College of Obstetricians and Gynecologists (ACOG) recommend that all pregnant women be screened. Repeat testing in the third trimester may be done for women at high risk. A woman who wants to make sure she is not infected with HIV before getting pregnant may opt to get tested. (see Pregnancy: Pre-conception, HIV).
The American Academy of Pediatrics (AAP) advises that all sexually active youth be screened, and that youths between 16 and 18 years old who live in high risk areas (areas where more than 1 in 1000 people have HIV) be offered HIV testing at least once, regardless of sexual history.
A health care worker with direct exposure to blood on the job
Any individual who thinks he may have been exposed
Timing of testing after suspected exposure is important. Antibody testing will not detect HIV immediately after exposure, during the window before the development of antibodies. The window period typically lasts from 2 to 8 weeks after exposure. If someone is tested too soon, the result may be negative despite the fact that the person is infected (false negative) and can transmit the disease to others. If an HIV test is negative but suspicion of exposure remains high, then repeat testing at a later time (usually 3 months after possible exposure) may be required. If available, a p24 antigen test may be performed, or a newer combination test that detects HIV antibody and p24 antigen may be ordered.
A healthy individual has no antibodies to HIV. However, a negative screening test means only that there is no evidence of disease at the time of the test. It is important for those who are at increased risk of HIV infection to have screening tests performed on a yearly basis to check for possible exposure to the virus.
If someone tests positive for HIV on both the initial screen and supplemental testing, he is considered to be infected with HIV. HIV cannot be cured, but early diagnosis allows for treatment that can help to suppress levels of virus in the body (viral load) and slow progression of the disease.
Urine HIV antibody tests are available, but they are less accurate (less sensitive and specific) than either blood or oral antibody tests. This CDC web page has more information on the different types of HIV screening tests available in the U.S.
This article was last reviewed on July 22, 2012. | This article was last modified on February 24, 2015.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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