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"How long after a potential HIV exposure should I wait to get my HIV test?"

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Updated December 05, 2010

Question: "How long after a potential HIV exposure should I wait to get my HIV test?"
After a possible exposure, people ask me, "when should I get my HIV test?" They realize that a possible exposure to HIV requires an HIV test, but how long after the exposure should HIV testing occur? That all depends on the situation.

How is HIV Infection Diagnosed?

Answer: The timing of your HIV test depends on many factors. Maybe the most important factor is the type of exposure that has occurred; namely were you exposed by a partner known to be HIV positive or a partner whose HIV status is unknown.

Partner - Unknown HIV Status
Most HIV tests diagnose HIV infection by detecting antibodies produced by an individual's immune system when they are exposed to HIV. However, it does take some time for enough of those antibodies to be present to be detected by the antibody HIV test. The time it takes for people to have produced enough antibodies varies; anywhere from 2 to 8 weeks or longer, with the average being about 25 days. But this can vary from person to person so a good rule of thumb to follow is if your negative test was done less than 3 months after your potential exposure, you should get another test after 3 months time. While about 97% of people will develop HIV antibodies after an infection, it may take 6 months to produce antibodies in some cases. In our clinic we recommend HIV testing after a potential exposure at 6 weeks, 3 months, and 6 months after exposure.

Partner - Known HIV Positive
Exposure to a known HIV positive partner is a situation that requires seeing a doctor as soon as possible; be it a primary care provider or in an emergency room setting. The reason for the urgency is the possibility that post exposure prophylaxis (PEP) will be initiated. Simply put, post exposure prophylaxis involves prescribing an HIV drug regimen after an HIV exposure to decrease the risk of infection occurring after the exposure. The timing of PEP has been proven to be more effective the sooner it is started; preferably less than 6 hours after the exposure but no more than 72 hours. The decision to start PEP is based on the type of exposure; for instance was the exposure through anal sex or by blood exposed to intact skin; the anal sex being a higher risk exposure and therefore necessitating PEP. The simple rule of thumb here is if you have been exposed by a partner whose known to be HIV positive you should see a doctor as soon as possible.

Important Note - PEP may be ordered in a person exposure by a partner with unknown HIV status if that partner is thought to be high risk (e.g. a known IV drug user).

Sources

California Department of Health Services; "Offering HIV Post-Exposure Prophylaxis (PEP) Following Non-Occupational Exposures"; California Office of AIDS; June 2004.

Centers for Disease Control; "Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings"; MMWR; 22 Sep 2006 / 55(RR14); 1-17.

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