The Hepatitis B Surface Antigen (HBsAg) blood test is a diagnostic test used to detect the presence of the Hepatitis B virus in the blood. The HBsAg protein is found on the surface of the Hepatitis B virus and is the first marker of the virus to appear in the blood after infection.

Hepatitis B is a serious liver infection caused by the Hepatitis B virus. The virus is spread through contact with the blood or other bodily fluids of an infected person. Hepatitis B can cause both acute and chronic infections, which can lead to liver damage, cirrhosis, and liver cancer.

The HBsAg blood test is typically performed as part of a screening panel for Hepatitis B. It is often used to diagnose acute and chronic Hepatitis B infections, as well as to determine if an individual is a carrier of the virus.

A positive HBsAg test result indicates the presence of the Hepatitis B virus in the blood. This could be an indication of an active infection or of chronic infection if the virus has been present for more than six months. A negative test result indicates the absence of the HBsAg protein and suggests that an individual is not infected with the Hepatitis B virus.

The HBsAg blood test is typically ordered for individuals who are at risk of exposure to the virus, including healthcare workers, individuals with multiple sexual partners, and individuals who use intravenous drugs. The test may also be ordered as part of routine health screenings or prior to travel to areas with high rates of Hepatitis B infection.

Treatment for Hepatitis B depends on the severity of the infection and may include antiviral medications, liver transplant, or other supportive therapies. It is important for individuals who test positive for HBsAg to work closely with a healthcare provider to develop an appropriate treatment plan.