Hepatitis B core antibody is the total antibody of hepatitis B virus core antigen, which has no protective effect and can be divided into anti -HBc IgM and anti -HBc IgG. Anti -HBc IgM is the first response antibody after HBV infection, and it is an important sign of acute or recent HBV infection. It usually lasts for about 6 months, and then gradually disappears. If it continues to be positive, it means that the virus replication in the body is active and easy to turn chronic. Therefore, low titer anti -HBc IgM can also be detected in the sera of patients with chronic hepatitis, primary liver cancer and some asymptomatic HBsAg carriers. After the disappearance of anti -HBc IgM, anti -HBc IgG appears, which can exist in serum for a long time and is a sign of HBV previous infection.