"Window period" in HIV is defined as

Period between onset of infection and clinically detectable level of antibody Window period The time period between primary infection and detection of antibodies is called window period. Traditional methods used in the diagnosis of HIV such as (ELISA and western blot) are based on the detection of these antibodies i.e., these tests become positive once the antibodies appear in the blood. However the recent methods used in the diagnosis of HIV are based on the detection of virus or virus paicles (not antibodies). Virus or the virus paicles appear early in the blood than antibodies so the newer methods have considerably reduced the period between the infection and the diagnosis i.e., they have reduced the window period Methods of detection Window period Antibody detection 22 days (ELISA western blot) p24 Antigen detection 16 days Nucleic detection 12 days