Clinical Significance

The hepatitis B virus consists of an outer envelope containing host-derived lipids and all S gene polypeptides, the large (L), middle (M), and small (S) surface proteins, also known as pre‑S1, pre‑S2 and HBsAg. The nucleocapsid contains core proteins HBcAg, a 3.2 kb, circular, partially double stranded viral DNA genome, an endogenous DNA polymerase (reverse transcriptase) enzyme, and protein kinase activity. The hepatitis core antigen comprises 183‑185 amino acids.

During an infection with the hepatitis B virus, antibodies to HBcAg are generally formed, which often persist for life. Anti‑HBc appears shortly after the onset of infection with hepatitis B virus and can usually be detected in serum soon after the appearance of HBsAg. Anti‑HBc antibodies persist
both in persons who have recovered from a hepatitis B infection and in those who develop HBsAg-carrier status. Accordingly, they are an indicator of existing or past hepatitis B infection.

In rare cases, an HBV infection can also run its course without the appearance of immunologically detectable anti‑HBc (usually in immunosuppressed patients). Due to the long persistence of anti‑HBc following a hepatitis B viral infection, screening for HBV infection may be accompanied by testing for the presence of hepatitis B core antibodies as long as those who test positive are further tested for 
both HBsAg and anti‑HBs to differentiate infection from immunity.Determination of anti‑HBc in association with other hepatitis B tests permits the diagnosis and monitoring of HBV infections. In the absence of other hepatitis B markers (HBsAg-negative persons), anti‑HBc may be the only indication of an existing hepatitis B viral infection.

_{Source: Roche cobas Elecsys Anti-HBs method sheet, V 2.0 2022-04}