I recently attempted to donate blood; however, I received a letter from the blood bank saying that I tested reactive for the presence of an antibody directed against the hepatitis B virus — core antigen (anti-HBC). In addition, they performed the hepatitis B surface antibody (HBsAb) test which was reactive.
I am 21-years-old and received the set of three immunizations against hepatitis B three years ago. I was wondering if you could tell me what having tested reactive for the hepatitis B core antibody means and how this could have happened if I was immunized.
Understanding the various tests used to clarify hepatitis B infection is indeed difficult, since there are several tests for different antigens (antigens are parts of the virus which elicit a response from an infected person) and antibodies. (Antibodies are the protective proteins which are produced by a person’s immune system in response to antigens.)
You mention two of the antigens found in the hepatitis B virus, and the antibodies your immune system has produced against them. These are the core antigen and antibody (anti-HBc), and the surface antigen (HBsAg) and antibody (anti-HBs, also called HBsAb). Core antigen is not usually measured, so I have not given a short hand identification for it, but the other three are routinely measured. In addition, there is an “e” antigen (HBeAg) and antibody (anti-HBe).
The antigens are actual parts of the virus particle, and their presence in a person’s blood means that he has active infection by the virus. When a person is first infected with the virus and develops hepatitis, HBsAg and HBeAg will both be present in the blood. Shortly afterward anti-HBc will appear. Although this is an antibody against one of the viral antigens, it is not protective and does not indicate that the immune system has overcome the infection.
In adults who are infected, about 95 percent do eventually overcome the infection, and this is indicated by the appearance of anti-HBs in the blood, and the disappearance of HBsAg. This conversion may take several months. If anti-HBs does not appear, and HBsAg persists in the blood, this indicates that the person has a chronic hepatitis B infection. In such a person we would then measure HBeAg, which if present means that the person is very infectious.
In people infected by hepatitis B from their mothers during infancy, the infant immune system is much less able to overcome the infection, and about 90 percent develop the chronic infection. This is the predominant mode of infection in Asia and Africa, and accounts for the many chronically infected people there. In the U.S. and Europe such transmission during infancy is uncommon, and most cases of hepatitis B are the result of sexual transmission, or from sharing needles among drug users. Pregnant women in the U.S. are now routinely tested for hepatitis B, and if they are chronically infected, their newborn child is immediately treated to prevent transmission of the virus.
The hepatitis B vaccine is composed of purified HBsAg. Since it is only a fragment of the live virus, it cannot cause hepatitis in a recipient. It does stimulate the development of anti-HBs, however, and this antibody then protects the recipient against future infection. Testing someone who has been immunized for anti-HBs will show if the immunization has been successful. A small percentage of people immunized (including me) do not develop anti-HBs, and probably remain susceptible to the infection.
Blood banks test for anti-HBc to determine if the person has ever been infected by the virus. The vaccine does not contain HBcAg, and therefore will not stimulate the development of anti-HBc so a vaccinated person will not show positive on this test. Since you are positive for anti-HBc, I would conclude that you have been infected at some time, either before you were immunized or after — the immunization may not have taken and failed to protect you.
Since you now have anti-HBs, you did not develop chronic hepatitis, and should not be infectious. You are also protected against future infection. About half of people infected by hepatitis B have no symptoms or only minor flu-like symptoms, so you might not have even known you were infected.
Many doctors and clinics will test a person for anti-HBc before giving the vaccine, since the vaccine is expensive, must be given as three injections over a six month period of time, and will be useless for someone who has already been infected. However, some clinics consider such testing to be simply another expense which rarely turns up a positive result, and thus don’t do it.
If you know that you were tested before you received the vaccine, and were negative, then your vaccination series did not produce immunity, or you may have been infected before you finished the full series. If you were vaccinated without being tested first, then you probably had already been infected before the vaccination.