If someone is HIV positive, they may have developed a detectable immune response as early as three weeks after exposure to HIV. After exposure, antibodies can take time to reach detectable levels, so using the self–test earlier than three weeks could produce false negative results even if the exposure had led to infection. However, for some people antibodies are not detectable until three months after exposure. This three–month period following exposure is known as the “window period.”
So, while a person may have a positive test at three weeks after potential exposure to HIV, if their result is negative, an HIV infection cannot be ruled out until three months after exposure. Individuals may choose to test within the window period of three months, but until a negative result is received after this period, HIV infection cannot be fully ruled-out.