The surface antigen of hepatitis B virus appears in the blood circulation of patients in the early stage of hepatitis B virus infection, and can last for months, years or even life. It is the most commonly used indicator for diagnosing hepatitis B virus infection. However, during the so-called window period of hepatitis B virus infection, the surface antigen of hepatitis B virus can be negative, while serological markers such as core antibodies of hepatitis B virus can be positive. Testing for hepatitis B virus surface antigen is used to determine whether you are infected with hepatitis B (hepatitis B) virus:
1.HBsAg positive is an indicator of hepatitis B virus infection, HBsAg itself has antigenicity, non-infectivity.
2. Other people with normal liver function and only HBsAg positive are called hepatitis B virus carriers.
3. The titer of HBsAg can determine the infectivity of patients. The higher the titer of a group of HBsAg, the more likely it is to be positive for HBsAg and HBV DNA, and the greater the infectivity.
4. “Dasanyang” : refers to the hepatitis B two-and-a-half test, hepatitis B surface antigen (HBsAg), E antigen (HBeAg) and core antibody (HBcAb) test are positive. It is suggested that hepatitis B virus infection, virus replication is active, infectious. It doesn’t indicate whether the condition is serious or not.
5. “Small three Yang” : refers to the hepatitis B two-and-a-half test, hepatitis B surface antigen (HBsAg), E antibody (HBeAb) and core antibody (HBcAb) test are positive. Tip:
(1) In most cases, hepatitis B virus replication is reduced. It’s still contagious.
(2) The shift from “Dasanyang” to “Xiaosanyang” does not mean that hepatitis B virus replication has completely stopped. A small number of “Dasanyang”  patients have continuous HBV-DNA positive serum, active viral replication, serious disease, rapid disease progression, and virus mutation.