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HIV window periods
Window periods are based on averages or statistics from studies. Different HIV tests have different window periods. As HIV testing technology improves, window periods may become more specific or even get shorter.
HIV tests used in British Columbia
These tests measure antibodies to HIV. Antibodies are proteins made by the immune system when the body is exposed to an infection. It takes time for the body to make antibodies after it is exposed to HIV, and different people make antibodies at different rates.
The window period for antibody tests is between 3 weeks and 3 months. Up to 95% of people will have antibodies after 6 weeks, and 99% of people will have antibodies after 3 months.
The point-of-care (or rapid) HIV test is an antibody tests offered in some locations in BC. The HIV Confirmatory Assay (Immunoblot test) is an antibody test used to confirm a preliminary positive HIV result.
The 4th generation Enzyme Immunoassay Test (EIA) test is a combined antigen / antibody test. The antigen, or viral protein, used to detect HIV is called p24 antigen. This p24 antigen shows up in the blood soon after a person gets HIV.
The 4th generation EIA test is the standard HIV laboratory screening test used in BC. Ninety-nine percent of these tests will be positive 6 weeks after a person gets HIV.
NAAT (Nucleic Acid Amplification Test)
This test looks for the genetic material of HIV in the blood. It is also known as the "early HIV test" or "RNA test". Ninety percent of NAATs are positive 10 to 12 days after a person gets HIV, and over 99% are positive after 6 weeks.
The RNA NAAT can be specially ordered by doctors or nurses if someone has had a recent high-risk exposure to HIV and/or they are having symptoms that are highly indicative of HIV.
The below graphs show the window periods for the different HIV tests available in BC. The shading shows the earliest time when a test could have a positive result. *Symptoms refers to symptoms of serconversion illness.
What happens at the laboratory?
When blood is sent to the BC Public Health Laboratory, the first test done is the 4th generation combined antibody/antigen test. Depending on results, the lab may continue with a second 4th generation antibody/antigen test, and/or an HIV confirmatory antibody test or a NAAT test.
What does this mean for me?
For most people, the best time to test is 3 weeks after having unprotected (condomless) sex with a new partner. If the test is negative, there is a good chance you do not have HIV from that sexual contact.
If you test at 6 weeks after having unprotected (condomless) sex with a new partner, and that test is negative, there is a 99% chance you do not have HIV from that sexual exposure.
With any HIV test, you should test again at 3 months to be sure.
Because HIV and other sexually transmitted infection (STI) rates are high in gay, bisexual and other men who have sex with men, routine screening every 3 months is recommended.