Patients with hepatitis B often talk about wanting to “remove the cap” and get a negative surface antigen. So what exactly is surface antigen and why is it called “cap removal”? Surface antigen is indeed a very important indicator in the treatment of slow hepatitis B. First of all, it is an important indicator of slow hepatitis B. First, it is a diagnostic indicator of slow hepatitis B. The surface antigen is the outer membrane of the hepatitis B virus, which is used by the virus to make close contact with the liver cells and invade them, making a healthy person a carrier of the hepatitis B virus. The outer membrane is produced by the virus itself, therefore, the presence of hepatitis B virus in liver cells is generally indicated by the detection of surface antigen in the blood. One of the current requirements for the diagnosis of slow hepatitis B is a persistent positive surface antigen for more than 6 months. In addition, surface antigen has a strong relationship with disease regression. According to current clinical studies, sustained low levels of HBV DNA (<10,000copies/ml) and HBeAg serological conversion both reduce the risk of cirrhosis and liver cancer in patients with slow hepatitis B. On this basis, if the surface antigen can be converted to negative, the annual risk of liver cancer is reduced to 0.02%, which is a very low percentage, compared to HBV DNA conversion alone, a decrease of This is a very low rate and a decrease of nearly 80% compared to HBV DNA alone. Surface antigen regression is recommended by authoritative guidelines as the ideal therapeutic endpoint for the treatment of chronic hepatitis B, and is the result of a recent clinical cure. It can be said that surface antigen conversion is the highest level of antiviral treatment efficacy, and that surface antigen conversion means a more stable treatment effect and freedom from the disease. Therefore, some people have compared this treatment result to "taking off the hat". In general, the current antiviral treatment regimen for chronic hepatitis B has a low rate of surface antigen regression, but long-acting interferon therapy has a relatively higher chance of achieving surface antigen regression, especially in patients with a higher pre-treatment transaminase level and a lower HBV DNA level, so it is worth trying interferon therapy to pursue higher treatment goals.