What does HBsAg stand for in the context of hepatitis B?

HBsAg stands for Hepatitis B surface antigen. This term refers specifically to a protein on the surface of the hepatitis B virus (HBV). The presence of HBsAg in a person's blood indicates an active hepatitis B infection, which could be either acute or chronic.

Identifying HBsAg is crucial for diagnosing hepatitis B, monitoring the disease progression, and determining the appropriate treatment options. The surface antigen is the part of the virus that the immune system targets when a person is vaccinated against hepatitis B, and it is also the antigen used in serological testing for detecting active infections.

The other terms in the choices do not accurately define HBsAg. For instance, "serum antigen" and "systemic antigen" don't align with the established terminology in medical literature. The phrase "sternal antigen" is not associated with hepatitis B at all. Therefore, Hepatitis B surface antigen is the correct and most widely recognized term used in clinical practice related to hepatitis B infection.