The Hepatitis B Surface Antigen (HBsAg) test detects the presence of the surface protein of the Hepatitis B virus in the blood. This antigen, historically called the “Australia antigen,” indicates an active Hepatitis B infection, which may be acute or chronic. Detection of HBsAg is the first marker to appear following infection and is used for screening, diagnosis, and monitoring of Hepatitis B infection.

The test is performed using CLIA (Chemiluminescent Immunoassay), a highly sensitive and specific method that identifies HBsAg through antibody-antigen binding, producing a measurable luminescent signal.