HBcAb, or the Hepatitis B Core Antibody Test

The hepatitis B core antibody (HBcAb, anti-HBc) is produced by your immune system after infection by the hepatitis B virus, and it can persist for life. It is a sign that you either have an new, active (acute) hepatitis B infection or that you acquired hepatitis B in the past.

HBcAb is an immune system response to a protein in the core of the virus, and it is only present if you have been infected, rather than immunized against the virus. It is part of a routine screening panel of tests for hepatitis B. If your rest results turn out to be positive, your healthcare provider will order further tests to determine the stage of the infection: acute or chronic (long term).

Being Tested for Hepatitis B Core Antibody

The hepatitis B core antibody test is part of a screening panel for hepatitis B, which also will include hepatitis B surface antigen (HBsAg) and hepatitis B surface antibody (anti-HBs). These three tests look for acute and chronic infections.

Tests may be ordered if you have symptoms of hepatitis, such as jaundice (yellowing of the skin and whites of the eyes), fever, fatigue, pale stools, dark urine, nausea, vomiting, and loss of appetite. In this case, the hepatitis B core antibody IgM test may be used, as it shows an early stage of infection.

This test may be ordered if you are being screened for hepatitis B because you are donating blood or wish to become an organ donor. Hepatitis B can be transmitted by blood or through organ transplants, so donors are tested to prevent infecting recipients. It's possible to have had the infection with only mild symptoms, so many people don't realize they have had hepatitis B.

The Centers for Disease Control and Prevention recommends all adults get screened at least once in their lifetime, including people who are not at risk and those without symptoms. Screening is also specifically recommended for pregnant people, people sharing a home with hepatitis B patients, people who may have been exposed by needlestick injuries or body fluids, and for people with HIV (human immunodeficiency virus).

How Is the HBcAb Test Done?

This is a blood test. A clinician will fill a tube with blood taken from a vein in your arm through which a needle is inserted. If you are giving blood, a sample will be taken from the blood you're donating. The blood is sent to a lab, where it is tested. Sometimes HBcAb will be added on to lab orders when results from other tests indicate there may be a hepatitis B infection.

Results of the HBcAb Test 

There are two variations of antibodies. The IgM antibody is the largest antibody and the first produced in an infection. It shows that you may have a current, active infection. Sometimes it persists for years, but it usually drops to undetectable levels once the acute infection resolves. 

The HBcAb IgG is produced later in the course of the infection, and it's likely that you will have a positive HBcAb IgG test for the rest of your life.

The screening panel usually has a test that is for total HBcAb, which includes both IgM and IgG. The IgM test may be ordered to help determine if you have an acute infection.

A positive HBcAb test must be interpreted along with the results of the other tests. You may have an active or chronic infection or be immune to hepatitis B due to past infection. Discuss the results with your healthcare provider. In any case, a positive HBcAb test (either an active or past infection) means your blood or organs cannot be donated to a recipient.