Hepatitis B antibodies are proteins formed in the body as a result of exposure to hepatitis B antigens, compounds carried on the envelope of the hepatitis B virus. Blood tests can be used to check for the presence of hepatitis B antibodies in a patient, and there are a number of reasons for them to be there, ranging from immunity as a result of vaccination to a recent hepatitis B infection. People may be screened for hepatitis B to see if a vaccination worked or to determine if they were exposed or infected. Turnaround times on blood tests vary, depending on the lab doing the processing.
If a person has an antibody to hepatitis B core antigens, it indicates a recent history of infection. The patient is not actively infected, but has carried the virus in the past and recovered. An antibody to hepatitis B surface antigen indicates that the body has developed defenses against the virus as a result of vaccination, and it will fight the virus if it is exposed. The presence of these hepatitis B antibodies means a vaccination worked and indicates that a hepatitis B booster is not needed, unless the antibody count falls very low.
Presence of hepatitis B antigens in the blood means someone has an active infection and the virus is replicating in the body. Two common examples are the hepatitis B surface and type E antigens. Both can be found in cases of chronic and acute infection. Patients with these antigens can pass the virus on to other people. They may also have some antibodies in the blood, the result of the immune system's efforts to learn to recognize the virus so it can tag viral cells for destruction.
A common reason to order a test for hepatitis B antibodies is to determine if a vaccine was effective, a concern in some patients, or to see if a patient needs a booster. While the regular three shot vaccine series for hepatitis B usually works, sometimes dosage differences and other problems inhibit the development of antibodies. For people like health care workers and individuals with a history of liver disease, it is very important to have full protection from hepatitis B, and antibody assay tests may be requested to see if they need another immunization.
Care providers may also want to check for hepatitis B antibodies to see if a patient had an infection recently, even if it is no longer present. This could explain symptoms and may also be important for tracing the history of hepatitis B infection in a group or community.