Hepatitis B core antibody (anti-HBc)
An antibody made against the inner core of the hepatitis B virus. Unlike the antibody from vaccination, it only appears after real exposure to the virus, so it marks past or present hepatitis B infection. It is read together with the surface antigen and surface antibody to build the full picture.
What it measures
The hepatitis B core antibody is an antibody the immune system makes against the inner 'core' of the hepatitis B virus. Its special value is that it only appears after genuine exposure to the virus itself — the hepatitis B vaccine does not produce it — so it distinguishes someone who has actually encountered hepatitis B from someone who is immune only because they were vaccinated. It is used as part of the hepatitis B panel, and it is interpreted together with two other markers: the surface antigen (HBsAg, which marks active infection) and the surface antibody (anti-HBs, which marks immunity). The combinations tell a story: core antibody positive with surface antigen positive means a current infection; core antibody positive with surface antibody positive but surface antigen negative means a past infection that has cleared, leaving natural immunity; core antibody positive alone can indicate a resolved infection or, occasionally, a hidden (occult) one. A separate core IgM version, when positive, points to a recent (acute) infection. Because it can flag a past hepatitis B that could reactivate, it is often checked before certain immune-suppressing treatments. This is a supportive marker read within the wider hepatitis B picture.
What a high value can mean
- Positive — past or present exposure to hepatitis B — the person has genuinely encountered the virus (not just been vaccinated).
- With a positive surface antigen (HBsAg) — a current, active infection.
- With a positive surface antibody but negative surface antigen — a past infection that has cleared, with natural immunity.
- The IgM form positive — points to a recent (acute) infection.
- Positive in isolation — may indicate a resolved infection or, occasionally, a hidden (occult) one; important before immune-suppressing treatment.
What a low value can mean
- Negative (non-reactive) — no evidence of past or present hepatitis B exposure.
- Immunity from vaccination — the core antibody is negative while the surface antibody is positive; this is how vaccine immunity is told apart from natural immunity.
When to discuss with a doctor
The core antibody is rarely acted on by itself — its value is in completing the hepatitis B picture alongside the surface antigen and surface antibody, so a doctor can tell current infection, past cleared infection, and vaccine immunity apart. A positive core antibody with a positive surface antigen means an active infection that needs assessment and follow-up. A positive core antibody with only the surface antibody positive usually means a past infection that has cleared, leaving immunity — generally reassuring. An isolated positive core antibody, and any positive result before starting immune-suppressing treatment or chemotherapy, is worth discussing, because hepatitis B can occasionally reactivate and may need preventive antiviral cover. Mediora.AI surfaces the core antibody alongside the other hepatitis B markers and liver tests so the combination can be read together; interpreting that pattern belongs with your doctor.