Blood tests

A patient who has an acute hepatitis B infection is diagnosed when a specific marker, or antigen, is found during the blood test. The antigen denotes the presence of an active, hepatitis B infection. The tests may remain positive throughout the early phases of the illness.

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Chronic hepatitis B infection is diagnosed when the presence of the antigen is found for more than six months. In a small number of patients who have the infection, the marker is not found during the blood tests. In those rare cases, doctors use blood tests that look for hepatitis B DNA to diagnose chronic infection. These patients have mutant type of hepatitis B, which may be associated with progressive liver disease.

Serum enzymes, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), are a sensitive tool for establishing a diagnosis of viral hepatitis. ALT and AST are the first enzymes to reveal abnormalities during the disease process and the last to normalize. They may reach levels 100 times the upper limits of normal during the acute infection. ALT is usually more abnormal than AST in the early and late stages of the disease.

Serum bilirubin--a byproduct of old red blood cells normally processed and removed from the bloodstream by the liver--at levels of 2.5 to 3.0 milligrams per deciliter or greater establishes the presence of the jaundice phase of hepatitis.