This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
"Window period" in HIV is defined as 
Select and explain. 
A. Period between onset of infection and clinically detectable level of antibodies, B. Period between infection and appearance of symptoms, C. Time between HIV positivity to AIDS, D. CD4 count < 200
A: Period between onset of infection and clinically detectable level of antibodies
Answer: A: Period between onset of infection and clinically detectable level of antibodies 
Explanation: 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