Viral hepatitis is a systemic disease primarily involving the liver. The complex antigen found on the surface of HBV is called HBsAg. Most cases of acute viral hepatitis are caused by Hepatitis A virus, Hepatitis B virus (HBV) or Hepatitis C virus. The complex antigen found on the surface of HBV is called HBsAg. Hepatitis B surface antigen (HBsAg) test is one of the most frequently performed tests for HBV infection.