Hepatitis B surface antigen is the hepatitis B virus shell protein, which itself is not infectious, only antigenic, but hepatitis B surface antigen often exists together with the hepatitis B virus, so hepatitis B surface antigen is also a sign of hepatitis B virus infection. If the quantification of hepatitis B surface antigen is relatively low, the hepatitis B virus HBV-DNA test should be performed, and if the hepatitis B virus HBV-DNA is negative, it is not infectious. If the hepatitis B HBV-DNA is positive, and when the load is high, it is infectious. In this case, you should consider whether antiviral therapy is needed, and it is better to choose antiviral therapy during the immune clearance period, and the preferred drugs are entecavir, tenofovir and pegylated interferon.