Clinical Significance

Hepatitis B core antigen (HBcAg) is a non-glycosylated protein (p22) which forms the nucleocapsid (virus core) of the hepatitis B virus. The virus core encloses the HBV‑DNA (virus genome) and the DNA-polymerase. In the cytosol of virus-producing hepatocytes the nucleocapsid is enveloped by the hepatitis B surface antigen (HBsAg) to form virions. Free HBcAg or nonenveloped virus cores are not detectable in serum. 

IgM antibodies to HBcAg occur in serum during proliferation of active hepatitis B virus and can still be detected weeks to months after viral proliferation has ceased. High anti‑HBc IgM concentrations can be found in acute hepatitis B and in attacks during chronic hepatitis B. 

Tests for detecting anti‑HBc IgM antibodies are used, in conjunction with HBsAg determinations, to identify acute hepatitis B viral infections. An acute attack of hitherto non-diagnosed chronic hepatitis B clinically resembles an acute hepatitis B infection and cannot be distinguished from this with 

certainty by determining the anti‑HBc IgM. Follow-up studies, imaging procedures and liver biopsies are useful in differentiating between these two clinical pictures.

_{Source: Roche cobas Elecsys Anti-HBc IgM method sheet, V 2.0 2024-12}