HBsAg is one of the earliest markers that appear in the blood following infection with HBV. HBsAg appears 1~7 weeks before biochemical evidence of liver disease or jaundice. Three weeks after the onset of acute hepatitis almost half of the patients will still be positive for HBsAg. In the chronic carrier state, the HBsAg persists for long periods (6-12 months) with no seroconversion to the corresponding antibodies. Therefore, screening for HBsAg is highly desirable for all donors, pregnant women and people in high-risk groups.

One step test for HBsAg Test is used for the qualitative determination of Hepatitis B surface antigen (HBsAg) in human whole blood, serum or plasma.