Hepatitis B (cont.)
How is hepatitis B diagnosed?
Infection with hepatitis B is suspected when the medical history and the
physical examination reveal risk factors for the infection or symptoms and signs
that are suggestive of hepatitis B. Abnormalities in the liver tests (blood
tests) also can raise suspicion; however, abnormal liver tests can result from
many conditions that affect the liver. The diagnosis of hepatitis B can be made
only with specific hepatitis B virus blood tests. These tests are known as
hepatitis 'markers' or 'serology.'
Markers found in the blood can confirm hepatitis B infection and
differentiate acute from chronic infection. These markers are substances
produced by the hepatitis B virus (antigens) and antibodies produced by the
immune system to fight the virus. Hepatitis B virus has three antigens for which
there are commonly-used tests - the surface antigen (HBsAg), the core antigen
(HBcAg) and the e antigen (HBeAg).
HBsAg and anti-HBs
The presence of hepatitis B surface antigen (HBsAg) in the blood indicates
that the patient is currently infected with the virus. HBsAg appears an average
of four weeks after initial exposure to the virus. Individuals who recover from
acute hepatitis B infections clear the blood of HBsAg within approximately four
months after the onset of symptoms.
These individuals develop antibodies to HBsAg (anti-HBs). Anti-HBs provides
complete immunity to subsequent hepatitis B viral infection. Similarly, individuals who are successfully vaccinated against
hepatitis B produce anti-HBs in the blood.
Patients who fail to clear the virus during an acute episode develop chronic
hepatitis B. The diagnosis of chronic hepatitis B is made when the HBsAg is
present in the blood for at least six months. In chronic hepatitis B, HBsAg can
be detected for many years, and anti-HBs does not appear.
Anti-HBc
In acute hepatitis, a specific class of early antibodies (IgM) appears that
is directed against the hepatitis B core antigen (anti-HBc IgM). Later, another
class of antibody, anti-HBc IgG, develops and persists for life, regardless of
whether the individual recovers or develops chronic infection. Only anti-HBc IgM
can be used to diagnose an acute hepatitis B infection.
HBeAg, anti-HBe, and pre-core mutations
Hepatitis B e antigen (HBeAg) is present when the hepatitis B virus is
actively multiplying, whereas the production of the antibody, anti-HBe, (also
called HBeAg seroconversion) signifies a more inactive state of the virus and a
lower risk of transmission.
In some individuals infected with hepatitis B virus, the genetic material for
the virus has undergone a structural change, called a pre-core mutation. This
mutation results in an inability of the hepatitis B virus to produce HBeAg, even
though the virus is actively reproducing. This means that even though no HBeAg
is detected in the blood of people with the mutation, the hepatitis B virus is
still active in these persons and they can infect others.
Hepatitis B virus DNA
The best marker of hepatitis B
virus reproduction is the level of hepatitis B
virus DNA in the blood. Detection of hepatitis B virus DNA in a blood sample
signals that the virus is actively multiplying. In acute hepatitis, HBV DNA is
present soon after infection, but is eliminated over time in patients' who clear
the infection. In chronic hepatitis, levels of HBV DNA often continue to be
elevated for many years and then decrease as the immune system controls the
virus. HBV DNA levels are sometimes referred to as the 'viral load'.
How are the hepatitis B blood tests interpreted?
The following table gives the usual interpretation for sets of results from hepatitis B
blood (serological) tests.
| Most Likely Status* |
Tests |
Results |
| Susceptible, not infected, not immune |
HBsAg
anti-HBc
anti-HBs |
negative
negative
negative |
| Immune due to natural infection |
HBsAg
anti-HBc
anti-HBs |
negative
positive
positive |
| Immune do to hepatitis B vaccination |
HBsAg
anti-HBc
anti-HBS |
negative
negative
positive |
| Acutely infected |
HBsAg
anti-HBc
IgM anti-HBc
anti-HBs |
positive
positive
positive
negative |
| Chronically infected |
HBsAg
anti-HBc
IgM anti-HBc
anti-HBs |
positive
positive
negative
negative |
*Interpretation of the hepatitis B virus blood tests should always be made by
an experienced clinician with knowledge of the patient's medical history,
physical examination, and results of the standard liver blood tests.
Next: What is the role of a liver biopsy in chronic hepatitis B? »
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