HBcAb, the hepatitis B core antibody, is positive and indicates that the person has been or is being infected with the hepatitis B virus, which can only be determined in conjunction with other indicators. Hepatitis B core antibody is the antibody produced by the body’s immune system against the hepatitis B core antigen. The intact hepatitis B virus is spherical in shape and consists of an envelope and a core coat, which contains the core protein (HBcAg), ringed double-stranded HBV-DNA and HBV-DNA polymutase, the center of hepatitis B virus genome replication. The core antibody is not easily detected in the blood because it is wrapped in the nuclear capsid, so the only serum marker for clinical detection of hepatitis B virus infection is the hepatitis B core antibody, which becomes the “half-pair” of the hepatitis B two-and-a-half pairs. The hepatitis B core antibody (IgG) can be detected in the serum of people who have been infected or are infected with the hepatitis B virus, so clinically it is necessary to combine the five hepatitis B items, hepatitis B virus nucleic acid and other viral markers for comprehensive analysis in order to correctly determine the condition of hepatitis B virus infection, for example, hepatitis B indicates negative antigen, positive core antibody, with or without positive surface antibody, all indicate a previous hepatitis B infection. For example, a negative hepatitis B indicator antigen and a positive core antibody, with or without a positive surface antibody, indicates a previous hepatitis B infection; a positive hepatitis B core antibody, along with a positive hepatitis B indicator antigen and/or hepatitis B virus nucleic acid, indicates a current hepatitis B virus infection. In addition, some hospitals will perform core antibody IgM testing, and a positive core antibody IgM indicates a recent infection or viral replication of the hepatitis B virus. Therefore, hepatitis B core antibody is a marker of previous or ongoing hepatitis B virus infection. A positive hepatitis B core antibody, along with the presence of hepatitis B indicating antigen and/or positive hepatitis B virus nucleic acid, indicates current infection with hepatitis B virus; otherwise, previous hepatitis B infection.