Approach to Diagnosis
Serological markers are useful for assessing for active or past hepatitis B infection.
Hepatitis B surface antigen (HbsAg) is indicative of active hepatitis B infection. This test does not distinguish between acute or chronic infection.
The hepatitis B surface antibody (anti-HBs) is indicative of past hepatitis B infection or past vaccination against hepatitis B. A positive surface antibody suggests immunity against the virus.
The hepatitis B core antibody (anti-HBc) is indicative of past or current hepatitis B infection.
Hepatitis B core IgM is also sometimes ordered when the anti-HBc is positive; a high titre of anti-HBc IgM is suggestive of acute infection and is useful for distinguishing acute and chronic hepatitis B.
Interpretation
- Surface antigen (HBsAg) - active (acute or chronic) infection
- Surface antibody (anti-HBs) - vaccination or past infection
- Core antibody (anti-HBc) - past or current infection
Phases of Infection
In patients with active hepatitis B infection, further tests are available for determining the phase and severity of infection.
The immune tolerant phase of hepatitis B infection is seen in very early infection and indicates active viral replication with no immune response. Most patients will progress to the immune active phase almost immediately, though some children infected with hepatitis B at birth will remain in the immune tolerant phase for many years. Hepatitis B DNA (HBV DNA) is a qualitative marker of viral replication, with high titres during the immune tolerant phase. The hepatitis B e-antigen (HBeAg) corresponds to infectivity and will be positive in this early phase of infection.
The immune active phase represents the immune system attempting to clear the infection. Active hepatitis will manifest as elevated ALT, while the HBV DNA titre will fall. The HBeAg may be positive; many patients seroconvert with development of anti-HBe antibodies during this phase.
The immune surveillance (or immune control) phase represents clearance of the infection. As hepatitis resolves the ALT will fall. Patients in this phase will remain hepatitis B carriers at risk of recurrence.
The immune escape phase (also known as HBeAg-negative chronic hepatitic B) occurs when the virus develops mutations to evade the control of the immune system and replicates, producing a recurrence in hepatitis and a high HBV DNA titre.
Interpretation
- E-antigen (HBeAg) - early infection
- Hep B DNA (HBV DNA) - level of viral replication
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