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What
are the Serum Markers of Hepatitis B and What do They Mean?
The main serum markers of hepatitis B are Hepatitis B Virus surface
antigen (HBsAg), HBV surface antibody (HBsAb), HBV e antigen (HBeAg), HBV
e antibody (HBeAb), and HBV c antibody (HBcAb). (They are commonly
referred to as the two and a half pairs and are usually used to identify
HBV infections.) The first two pair of markers are obvious but
because HBV c antigen is quickly degenerated in the serum, it cannot be
tested in the serum. If any one of these markers test positive, it
means that the person has had a HBV infection. If HBsAg, HBeAg, and
HBcAb test positive, it means that the HBV is replicating actively and the
patient is infectious.
Individually, these markers each have their own significance. HBV surface
antigen (HBsAg) is the surface protein of HBV. The HBsAg itself is not an
infectious agent but its existence shows that there is HBV in the body of
the patient. (It has the same meaning as having detectable HBV DNA in the
blood.) HBsAg can exist in blood, saliva, breast milk, sweat, tears, nasal
secretions, semen, and vaginal secretions. It becomes positive in the
serum within 2 to 6 months of the initial HBV infection and usually two to
eight weeks before ALT and AST elevation. In acute HBV infections, it can
turn negative in the early stage of the disease course. In chronic
hepatitis B patients, this marker can be persistently positive.
The HBV surface antibody (HBsAb) is the product of the body’s immune
reaction to the HBV infection. It is an immune globulin secreted by B
lymph cells that can combine with the HBsAg to neutralize it. Along with
other immune reactions, the HbsAb protective antibody can eradicate the
invading HBV from the body. Either an HBV infection or HBV vaccination can
cause the HBsAb marker to be positive. This antibody can exist in the
blood for a long time, gradually decreasing with age. If the HBV infection
happened during the infancy period, it is likely to become chronic since
the infant is unable produce this antibody at that time.
The HBV e antigen (HBeAg) comes from the core of the HBV and is a portion
of the core. When the core of the HBV degrades in the serum, this antigen
is created and can be detected. Because HBcAg will be totally degraded in
the serum, it is not detectable in the serum. Thus, when the HBeAg marker
becomes positive, it is equivalent to a positive HbcAg marker and shows
that the Hepatitis B virus is replicating actively and the patient is
infectious.
The HBV e antibody (HBeAb) is the body’s immune reaction to the HBeAg
and like HbsAb, it can combine with the HbeAg. It usually appears after
the HBeAg turns to negative, which also means that the HBV replication
activities have decreased and the patient is less infectious or not
infectious at all.
This overview of HBV serum markers gives us a dynamic view of the HBV
infection and we can use them to evaluate the HBV replication and the
infectious level of the patient.
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