Hepatitis B core antibody positive: what it means

Hepatitis B serology is reported as several markers, and the core antibody is one of them. The core antibody (anti-HBc, sometimes written HBcAb or anti-HBcore IgG) rises when the immune system has been exposed to the hepatitis B virus. Unlike surface antibody (anti-HBs), it is not produced by the vaccine, so a positive result means natural exposure to the virus at some time.

The most common explanation, when the surface antigen is negative, is an infection in the past that the body has cleared. An NHS Greater Glasgow and Clyde reactivation guideline calls this a "resolved" or "cleared" infection. It is not usually a cause for alarm in itself, but it is something that doctors record, because the virus can in rare circumstances become active again.

The NHS says hepatitis B is a liver infection spread through blood and body fluids that usually lasts for 1 to 3 months, and that most people with it have no symptoms or mild symptoms. Many people who tested positive for core antibody will never have known they were infected.

No single marker tells the whole story, which is why hepatitis B tests are usually reported together. The guideline sets out what each result indicates.

The guideline explains that reactivation means an abrupt increase in the virus in someone with minimally active or resolved infection. It happens when the immune system is deliberately suppressed, for example during cancer chemotherapy, after stem cell or organ transplantation, or when taking certain biological medicines. The timing varies; it may occur within the first 2 weeks of chemotherapy or more than a year after immunosuppression stops.

It describes an asymptomatic early phase in reactivation that gives a window to start treatment, which is the rationale for checking markers before immunosuppression. This is why people about to start such medicines are screened. The guideline lists transplant recipients, those having cancer chemotherapy, and people in rheumatology, gastroenterology and dermatology due to receive biologic or other immunosuppressive therapies, for example for lupus, rheumatoid arthritis, vasculitis, psoriasis, inflammatory bowel disease or autoimmune hepatitis.

Most people with a core-antibody-positive result are never on such a treatment, and for them the result has no practical consequence beyond being recorded. The decision about what to do sits with a specialist when treatment is planned.

The guideline divides the risk of reactivation by the type of immunosuppression. For people who are HBsAg negative and core antibody positive with undetectable DNA, it gives the following broad picture.

• Higher risk (10% or more): rituximab, and bone marrow or stem cell transplant recipients. Preventive antiviral treatment is recommended.

• Low to moderate risk (under 1% to under 10%): for most, monitoring rather than prophylaxis is generally recommended. Solid organ transplant recipients, for example, are described as low risk with monitoring only.

• Low risk (under 1%): the guideline lists azathioprine, methotrexate, intra-articular steroids and short courses of oral steroids among treatments that carry a low risk of reactivation.

• For monitoring, it suggests liver function tests and HBsAg, with or without HBV DNA, every 3 months during and for 12 months after immunosuppression, and says not to repeat the core antibody test.

The guideline defines occult HBV as HBsAg negative, core antibody positive, but with repeatedly detectable HBV DNA. It says occult HBV is rare, and that these patients should be managed as if they were HBsAg positive. That is why a DNA test is added when core antibody is found before immunosuppression, rather than assuming the infection has cleared.

The guideline also notes that very low DNA levels in an HBsAg-negative person can sometimes reflect laboratory contamination, and recommends discussing unexpected results with the virology laboratory.

If you have no immunosuppressive treatment planned, a clinician may simply record that you have had past hepatitis B and may check liver function and the other markers to confirm the pattern. If immunosuppression is planned, the guideline says patients at potential risk should be discussed with infectious diseases, hepatology or virology specialists in advance of starting treatment.

The NHS says to see a GP if you think you might have hepatitis B or are at high risk of getting it, and lists symptoms that can occur, including yellowing of the skin and whites of the eyes, dark urine and pale poo. The NHS also advises avoiding alcohol and not sharing razors, toothbrushes or needles if you have hepatitis B.

This guideline comes from one Scottish health board and is cited as an example of UK practice. Local policies differ in detail, so your own specialist team will follow the arrangements used where you are treated.