Hepatitis B surface antigen assay is one of the virological markers of hepatitis B. When human body is infected with hepatitis B virus, hepatitis B surface antigen appears first, and it has positive correlation with the level of hepatitis B virus replication. If the human body is infected with the hepatitis B virus and is not tested and treated regularly, it may progress to hepatitis B cirrhosis and liver cancer. Hepatitis B surface antigen measurement can also be used to evaluate the efficacy of antiviral therapy, when quantitative testing of hepatitis B surface antigen is required.