HIV antibodies at 3 or 6 months

Originally Published: March 15, 1996 - Last Updated / Reviewed On: August 31, 2009
Share this
Dear Alice,

What is the percentage of people who develop enough antibodies for HIV virus in the first three months after exposure? Does the length of window period depend only on the response of one's immune system or also on the amount of infectious fluid that was transferred during sex?


Dear Interested,

You're right to point out that it can take time for the body to produce enough antibodies for an HIV test to detect. This "window period" varies from person to person, but the average time it takes for a person to develop antibodies is 25 days. After three months, 97 percent of people who are infected with HIV will have enough antibodies to test positive. For this reason, if a person tests negative for HIV within the first three months after they may have been exposed, it's recommended that s/he gets a repeat test after three months have passed. Although a higher volume of body fluid can increase the risk of transmitting the virus, the amount of infected fluid transferred won't affect the window period.

Getting tested after three months helps decrease the likelihood of a false negative (i.e., a person who is HIV-positive but tests negative). A person who tests negative after three months is probably not infected. Rarely, it can take up to six months for an infected person to test positive, but repeat testing after six months have passed is only suggested if the person has a high risk of contracting HIV — for example, s/he had sex without a condom with a partner known to be HIV-positive — or if the person or his/her health care provider is still concerned. Generally, extended testing beyond the six-month mark isn't recommended.

Keep in mind that it can be difficult to pinpoint when a person was exposed to HIV and thus whether enough time has passed to be confident in the test results. Rather than try to figure out if three months have passed since exposure, some people choose to get tested at regular intervals, especially if they are consistently at some risk for HIV.

Columbia students can access free and confidential HIV testing through the Gay Health Advocacy Project (GHAP) on a walk-in basis. For more information about HIV and AIDS, call the CDC HIV/AIDS Hotline at 1.800.CDC.INFO (232.4636), or check out the Columbia University Handbook on HIV and AIDS.

Here's to staying informed,