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ABSTRACT: Serum levels of aspartate aminotransferase and alanine aminotransferase that exceed 1000 IU/L indicate acute viral hepatitis (A, B and, rarely, C), acute drug toxicity (eg, acetaminophen overdose or isoniazid hepatotoxicity), or ischemic liver injury. In chronic hepatitis (ie, hepatitis B or C or autoimmune), values range from mildly elevated to usually less than 400 IU/L. Elevated levels of alkaline phosphatase and gamma;-glutamyltransferase (GGT) are consistent with cholestatic disease: primary biliary cirrhosis, primary sclerosing cholangitis, idiosyncratic drug reactions, or mechanical biliary obstruction (eg, biliary stones or tumor). Elevation in the GGT level can also be induced by alcohol consumption or medications (eg, phenytoin). Isolated unconjugated hyperbilirubinemia suggests Gilbert syndrome or a hematologic disorder; conjugated hyperbilirubinemia reflects impaired hepatic excretion. Serum bilirubin and albumin and INR have prognostic significance in chronic liver disease; bilirubin and INR are more useful in acute liver failure because albumin has a long half-life.