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Hepatitis B markers
"The two and half pairs"
This refers to the two pairs of markers (HBsAg and HBsAb, HBeAg and
HBeAb) plus the HBcAb test (the half). The HBcAg will be totally
degraded in the serum, it is not detectable in the serum.
When combined these tests are used to diagnose and evaluate HBV
infection. In order to evaluate hepatitis markers the physician needs
to address a series of questions:
1. Does the patient have HBV infection?
HBsAg (Hepatitis B surface Antigen)
- Becomes positive in the serum within 2 to 6 months of the
initial HBV infection
- The first evidence of hepatitis B infection ( two to eight weeks
before ALT and AST elevation)
- Establishes infection with HBV
- Implies infectivity
- Persistence after acute illness denotes carrier state and may
indicate chronic hepatitis infection.
2. Is the virus actively replicating?
HBeAg (Hepatitis Be Antigen)
- Denotes viral replication and infectivity
- Persistence 3 months after the acute phase suggests chronic
infection
Infection caused by mutant forms of HBV leads to absence of HBeAg in
serum. This is where HBV-DNA must be measured to determine
infectivity.
3. Is the patient infective?
The presence of the antigens (HBsAg, HBeAg) in blood denotes
infectivity. However, after the disappearance of HBsAg and before the
appearance of HBsAb (which denotes cure), there is a window period
(serological gap) in which the patient is still infective but there is
no HBsAg in the blood. To detect infectivity during this period HBcAb
(IgM) is used.
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HBcAb (IgM)
- Detects infectivity during the serological gap.
HBeAb
- Appears after HBcAb and implies decreasing infectivity
4. Is the patient cured?
Disappearance of HBsAg and appearance of HBsAb denotes recovery,
noninfectivity and protection from recurrent HBV infection.
HBsAb
- Denotes recovery from HBV or successful vaccination.
Persistence of the antigens (HBsAg, HBeAg) for 3 months after the
acute phase of the disease suggests chronic hepatitis.
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