The appropriate selection of investigations for hepatitis B depends on an understanding of the virus itself, how illness occurs and the natural history of the infection.
- Hepatitis B virus (HBV) infection is present when HBsAg is detectable in the serum.
- Appropriate investigation of a patient who is HBsAg positive depends on the clinical scenario, and relies upon an understanding of the virus, the serological markers used, how illness occurs, and the natural history of HBV infection.
- In acute hepatitis, investigation is directed towards deciding whether the episode is due to HBV or another cause; if HBsAg is detected, whether the episode represents a new infection or a flare of chronic HBV infection needs to be considered.
- Investigation in the more common scenario of chronic infection in an asymptomatic person is directed mainly towards defining the stage in the natural history of HBV infection and the state of the liver.
- In chronic infection, active liver disease (abnormal ALT) and viral replication (positive HBeAg or HBV DNA) identifies patients who are at increased risk of liver injury but may respond well to antiviral therapy.
- Specialist referral is important when active liver disease is present, irrespective of the state of viral replication, and when cirrhosis or hepatic decompensation is evident.