Most HIV tests, including most rapid tests and home tests, look for antibodies. Antibodies are produced by your immune system when you’re exposed to viruses like HIV or bacteria. HIV antibody tests look for these antibodies to HIV in your blood or oral fluid. It takes time for the body to produce enough antibodies for an HIV test to show that a person has HIV. The tests become accurate around four weeks following an infection. Most (approximately 97%), but not all, people will develop detectable antibodies within 3 to 12 weeks (21 to 84 days) of infection.