what is hbsag test

The HBsAg test is a blood test that looks for hepatitis B surface antigens in the blood. The test is used to determine if a person has a recent or long-standing infection from the hepatitis B virus (HBV) . A positive or reactive HBsAg test result means that the person is infected with hepatitis B. This test can detect the actual presence of the hepatitis B virus (called the “surface antigen”) in the blood. If a person tests positive, further testing is needed to determine if this is a new “acute” infection or a “chronic” hepatitis B infection. A positive HBsAg test result means that the person is infected and can spread the hepatitis B virus to others through their blood. The HBsAg test is routinely used to diagnose suspected HBV infection and monitor the status of infected individuals to determine whether the infection has resolved or the patient has become a chronic carrier of the virus.