antiHBc

anti‑HBc (antibody to hepatitis B core antigen) is an immunoglobulin produced in response to the hepatitis B virus (HBV) core protein (HBcAg). The presence of anti‑HBc indicates exposure to HBV, because the core antigen is not present in the vaccine; therefore anti‑HBc is not generated by immunisation alone. Anti‑HBc appears early in acute infection, usually within 1–2 weeks after the onset of symptoms, and persists indefinitely, allowing it to serve as a marker of past or ongoing infection.

Two classes of anti‑HBc are clinically relevant: IgM anti‑HBc and IgG anti‑HBc. IgM anti‑HBc is detectable during the acute phase or during an HBV flare in chronic disease and typically declines within six months. Its detection is useful for diagnosing recent infection and for identifying the “window period,” when hepatitis B surface antigen (HBsAg) has disappeared but hepatitis B surface antibody (anti‑HBs) has not yet appeared. IgG anti‑HBc appears later, remains positive for life, and signifies prior exposure or chronic infection. In chronic hepatitis B, IgG anti‑HBc is usually present together with HBsAg; loss of HBsAg with persistent IgG anti‑HBc suggests resolved infection.

Laboratory testing for anti‑HBc is performed using enzyme‑linked immunosorbent assay (ELISA) or chemiluminescent immunoassay, often as part of a hepatitis B serologic panel that includes HBsAg, anti‑HBs, and HBV DNA. Interpretation relies on the pattern of markers: isolated anti‑HBc may indicate a false‑positive result, a resolving acute infection, or occult HBV infection, and further testing is required. Anti‑HBc does not confer immunity; protective immunity is indicated by the presence of anti‑HBs in the absence of HBsAg and anti‑HBc.