Hepatitis B core antigen (HBcAg) is an intracellular antigen synthesized within infected hepatocytes and is expressed by infected hepatocytes only. Most of the generated HBcAg is assembled into the viral core (nucleocapsid). Free HBcAg does not circulate in significant quantity in the blood, but it does circulate as part of the intact hepatitis B virion. So HBcAg is not detected in serum tests, but antibodies produced against HBcAg, i.e. (anti-HBc), can be detected in the serum throughout HBV infection.