hbsag is a hepatitis B surface antigen that can be present along with the hepatitis B virus and is one of the commonly used tests to determine the presence or absence of hepatitis B. In addition to hepatitis B surface antigen, there are also hepatitis B surface antibodies, hepatitis B e antigen, hepatitis B e antibody, hepatitis B core antibody, and hepatitis B core antigen. These are collectively known as the hepatitis B triple system. Hepatitis B surface antigen can be found in all of a patient’s body fluids, including various exocrine secretions. If a patient is positive for hepatitis B surface antigen, he or she is infected with the hepatitis B virus. It is necessary to regularly review the five hepatitis B tests, liver function, hepatitis B DNA, abdominal ultrasound and other tests to dynamically monitor the changes in the hepatitis B condition in order to take the right treatment plan. If the hepatitis B surface antigen is negative, it means there is no hepatitis B. However, at this time, we need to pay attention to see whether the hepatitis B surface antibody is negative, if the hepatitis B surface antibody is negative, it means there is no protection and hepatitis B vaccination is needed; if the hepatitis B surface antibody is positive, it means there are antibodies in the body, which can protect from being infected by the hepatitis B virus. Therefore, hbsag indicates the marker of hepatitis B, which is an important clinical sign to determine whether hepatitis B is present or not. It is recommended to do hepatitis B five tests at the hospital to help clarify the diagnosis.