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      #22748 - 09/26/01 08:21 AM

HIV Antibody Assays

HIV InSite Knowledge Base Chapter
Published February 1998
Niel Constantine, PhD, University of Maryland School of Medicine

Specific antibody to HIV is produced shortly after infection, but the exact time depends on several factors, including host and viral characteristics. Importantly, antibody may be present at low levels during early infection but not at the detection limit of some assays. Using the early generation tests, antibody could be detected in most individuals by 6 to 12 weeks after infection. Newer generation assays, including the third-generation antigen sandwich assays, can detect antibody at about 3 to 4 weeks after infection.(2) As discussed in other chapters, this window period before the detection of antibody can be shortened by several days using antigen tests, and by several more days using nucleic acid detection methods.(3) Therefore, in most individuals, the window period may only be 2 to 3 weeks if an all-inclusive testing strategy is used. Most antibody tests currently on the market have near perfect and equivalent degrees of sensitivity for detecting most individuals who are infected with HIV (epidemiologic sensitivity), but they vary in their ability to detect low levels of antibody (analytical sensitivity), such as that occurring before complete seroconversion.(2) Although tests are available to detect specific HIV IgM antibody, these tests have shown little utility in identifying early infection because IgM responses to HIV are not consistently produced during early infection.(4) The ability of some tests (e.g., third-generation tests) to detect IgM antibody simultaneously with IgG detection, however, may be responsible for their higher analytical sensitivity.


The time period between a person’s actual infection with HIV and until HIV antibodies become detectable in blood or other fluids is called the "window period". Most people will develop antibodies detectable with the latest blood tests within 4-6 weeks after infection with HIV. Some people may take longer; but nearly all (99%) will have antibodies by 3 months following infection. Therefore, we recommend that people wait 3 months from the time of the possible infection with HIV (the date of latest exposure) before being tested for HIV antibodies. The test may not give an accurate negative result if a person gets tested too soon after a potential exposure.

People waiting three months from the time of the exposure before testing will have a 99% accurate test result. Very rarely, cases have been reported of people taking longer than three months to develop antibodies to HIV.

Public Health
Seatlle & King County

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