HBsAg Hepatitis B Surface Ag Test Strip HBsAg test is a rapid direct binding test for the visual detection of hepatitis B antigen (HBsAg) as an aid in the diagnosis of hepatitis B infection.It is based on the principle of sandwich immunossay for determination of HBsAg in human serum specimen.Two monoclonal antibodies are employed to identify HBsAg specifically.This one step test is very sensitive and only takes about 15-20 minutes.