Testing for HIV (Human Immunodeficiency Virus) 19 days after high-risk behavior does not completely rule out infection. There is a period of time between HIV infection and the body’s production of antibodies, which is called the window period, during which antibodies cannot be detected even if the person is infected. The length of the window period varies from person to person, but the upper limit is usually 3 months. 19 days after high-risk behavior may be in the window period, so the test is meaningless. It is recommended to take the test 3 months and 6 months after the risky behavior. If the results of both tests are negative, HIV infection can be ruled out. It is recommended to go to the hospital to take blood test for HIV antibody after the risky behavior, and review the test under the guidance of the doctor, and if the test result is negative after the window period, the infection can be ruled out in general.