Hepatitis B Surface Antigen Rapid Test is a qualitative detection of hepatitis B surface antigen (HBsAg) in human serum and plasma specimen. This test is used as an aid in the diagnosis of hepatitis B virus (HBV) infection. Hepatitis B virus is a DNA virus belonging to Hepadnaviridae. HBsAg is the coat protein of hepatitis B virus. HBsAg can appear in human blood after a person is infected with hepatitis B virus, which is a sign of HBV infection.