HIV Testing (cont.)

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How long does it take to get results back from an HIV test?

Results from antibody tests that are sent to a laboratory usually take one to three days to return. If the test is positive, results may be delayed while the laboratory does a Western blot to be sure that HIV antibody is present. Western blot tests take only one day to perform, but some laboratories may not run the test every day. Results from rapid tests done in the doctor's office or at other points of care are usually available in 15-20 minutes. If the rapid test is positive, it is still necessary to send blood to a laboratory for a Western blot to be sure the rapid test result is correct. Home tests are mailed to a laboratory, and results return in one to two weeks. RNA testing results usually take a few days to a week, depending on the lab.

Is counseling offered with HIV testing?

Each state establishes requirements for HIV counseling. Most states have supported an "opt out" testing program in which people are recommended to have HIV testing but may opt out if they choose. Such programs should include counseling about HIV, including prevention of infection, the meaning of the HIV test, and the need for appropriate follow-up. Opt-out programs have resulted in earlier diagnosis of many people with HIV.

HIV testing may sometimes be done if a health-care worker or first responder (policeman, fireman, emergency medical technician, etc.) has significant exposure to the blood or body fluid from an identifiable person. In this situation, testing without consent is available in most states. All blood and plasma donors, some prisoners, and some military personnel are tested for HIV.

What is the likelihood of receiving a false positive or false negative with an HIV test?

The current testing protocols are highly accurate but not perfect. The probability of a false result on the test depends on the test and on the likelihood that the person is infected.

Falsely negative tests occur in people who are truly infected with HIV but have negative tests. Among 1,000 people who are truly infected, rapid tests will be falsely negative in zero to six people, depending on the test. Negative antibody tests in people infected with HIV may occur because antibody concentrations are low or because antibodies have not yet developed. On average, antibodies take about four weeks to reach detectable levels after initial infection, and falsely negative tests may occur during this so-called HIV window period. Individuals with negative tests and who had high risk for HIV exposure should be retested in two to three months.

Falsely positive tests occur when uninfected people have positive tests. Among 1,000 people who do not have disease, rapid tests will be falsely positive in zero to nine people, depending on the test. This is the main reason for not relying on a single positive test for diagnosis. As discussed above, all positive initial tests must be confirmed with a Western blot. When both tests are positive, the likelihood of a person being HIV infected is >99%. Sometimes, the Western blot may be indeterminate, meaning that it is neither positive nor negative. In these cases, the tests are usually repeated at a later date or an RNA test is done.

Medically Reviewed by a Doctor on 4/9/2014


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