Hepatitis B virus core antibody, a marker of early acute infection with viral hepatitis B, can be present in the serum for a long time. Its titer can reflect the replication of some viruses, and if the titer is high, it indicates that the virus is replicating. Core antibodies to hepatitis B virus are important in the diagnosis and identification of hepatitis B. They are also important in differentiating the typing of viral hepatitis. A positive core antibody to the hepatitis B virus indicates that a person with hepatitis B has been previously infected, or is currently infected with the hepatitis B virus. It can distinguish some other conditions that can be checked for its two subtypes, such as core antibody IgM and IgG. High titers of hepatitis B core antibody IgM are an important indicator of acute or recent infection. It is also positive during the active phase of chronic hepatitis, signifying that the hepatitis B virus is replicating and is a sign of previous infection with the hepatitis B virus. Core antibody IgG can be present for ten or more years and indicates recovery.