Hepatitis B Surface Antigen (HBsAg) Test :
A blood test that detects the presence of the Hepatitis B surface antigen (HBsAg), a protein found on the surface of the Hepatitis B virus (HBV). The presence of HBsAg in the blood indicates an active Hepatitis B infection , whether acute or chronic. It is one of the first markers to appear during an infection. A positive result means the person is infectious and capable of transmitting the virus to others. If HBsAg persists for more than six months, it suggests a chronic Hepatitis B infection, which may require ongoing monitoring and treatment.