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Understanding HIV testing
HIV tests look for markers of infection; timing after a possible exposure affects how reliable a result is.
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What HIV tests look for
HIV tests detect antibodies and, in some laboratory tests, antigens produced in response to the virus. Finger-prick self-tests generally detect antibodies.
The window period
After exposure it takes time for the body to produce detectable markers. The NHS advises that self-tests may not detect HIV that was acquired recently, and a negative result may need repeating after the window period stated in the kit instructions.
If you think you were exposed in the last 72 hours, contact a sexual health clinic or A&E promptly about post-exposure prophylaxis (PEP). A home test cannot help in this situation.
After a reactive result
A reactive self-test result is not a diagnosis. It must be confirmed with a laboratory test at a sexual health clinic or GP. HIV is a manageable long-term condition with effective treatment, and support services are available.
Related on CareFree Kits
Sources
- NHS – HIV and AIDS (nhs.uk/conditions/hiv-and-aids)
Last reviewed 5 November 2026. This guide has not been clinically reviewed by a named professional.