What is the hepatitis B surface antibody?

The hepatitis B surface antibody is one of several antibodies that may be detectable in the body that is indicative of the presence of hepatitis B, according to WebMD. The HBsAb test is designed to specifically identify this antibody.

WebMD explains that doctors may first test for hepatitis B surface antigens, which identifies an active, contagious or chronic hepatitis B presence in the body. Hepatitis B surface antibodies generally appear about four weeks after the surface antigens are gone. If they are detected, it signifies the end stages of the hepatitis B infection, and that the person is no longer contagious. The HBsAb also determines if a vaccination is necessary, as the presence of surface antibodies protects the person from getting hepatitis B in the future.