Anti-HBc (IgG and IgM) antibodies are the body’s first response to a hepatitis B virus (HBV) infection. These antibodies are directed against a portion of the HBV called the core. IgM anti-HBc antibodies appear shortly after the symptoms and appearance of HBsAg. They last 4 to 8 months (sometimes up to 2 years) and are then replaced by IgG anti-HBc antibodies. IgM anti-HBc results are interpreted in light of HBsAg and anti-HBs results, among others.
A negative IgM anti-HBc result may indicate that there is no recent or previous HBV infection (negative HBsAg, anti-HBs and IgG anti-HBc) or that the individual is in the acute phase of the disease and has not yet built up a defence (positive HBsAg, negative anti-HBs) or that the virus has been reactivated in a chronic carrier. IgM (and IgG) anti-HBc will also be negative in a successfully vaccinated individual.
A positive IgM anti-HBc result indicates that the body has begun to defend itself against HBV. When combined with a negative HBsAg, the recovery period is underway and the IgG anti-HBc test is expected to quickly become positive. If HBsAg is still positive, the individual is either still in the acute phase of the disease and the combination of positive HBsAg/IgG anti-HBc / negative anti-HBs may indicate an active chronic infection.