Abnormal liver function test results – Quick Reference

This is a Quick Reference article. See also the main article Assessing a patient with an abnormal liver function test result .

Liver enzymes

• ALT (alanine aminotransferase) is principally a liver cell enzyme, and only small amounts are encountered elsewhere. ALT is the first-line screening test for a liver disease.
• AST (aspartate aminotransferase) is less specific. In addition to liver cells, it may be released into blood stream from muscles, red blood cells, kidneys and brain.
• GT (glutamyl transferase) is a sensitive but non-specific marker of liver damage. Increased concentration may be due to hepatocellular damage, cholestasis or, for example, drug-induced enzyme induction.
• Alkaline phosphatase originates from biliary ducts or bones.
• Slight increase = 2–5 × the upper limit of reference range; encountered in about 10% of population.

Most common causes of mild increase

• Fatty liver
  • Alcoholic: AST higher than ALT (ratio > 1). Even moderate alcohol consumption can increase GT.
  • Non-alcoholic (NAFLD), most commonly associated with metabolic syndrome: ALT higher than AST
  • Associated with obesity with increasing frequency.
• Chronic viral hepatitis
  • ALT is normal to slightly increased in hepatitis B.
  • Usually between 80 and 200 IU/l in hepatitis C.
• Liver cirrhosis
  • In asymptomatic cirrhosis, ALT and AST are only slightly increased. If clinical picture is suggestive of liver cirrhosis, check other liver function tests: albumin, prealbumin, bilirubin and INR.
• Drug-induced and other toxic injury
  • If suspected, stop the drug immediately and check levels again after a few days to weeks.
• Autoimmune liver disease
  • Primary biliary cirrhosis , primary sclerosing cholangitis : alkaline phosphatase increases the most, AST and ALT may remain normal.
• Rare causes
  • Storage diseases (iron, amyloidosis), vasculitis, Wilson’s disease

Investigations

• Incidental finding
  • History (alcohol, medication, illegal substances, blood transfusions, natural remedies)
  • If asymptomatic, re-check after 2–3 months.
  • Stop the drug if drug reaction is suspected, re-check within about one week.
• Excessive alcohol consumption
  • Abstinence for 1 month then re-check
• Diagnostics of viral hepatitis: see Viral hepatitis
• Upper abdominal ultrasonography
  • Inadequate sensitivity and specificity in parenchymal disease
  • Suitable for the investigation of focal changes and biliary tract disease.
• Liver biopsy in specialist care, does not require hospitalisation. Assess bleeding risk (blood platelets, INR/thromboplastin).
• Indications for liver biopsy
  • Persistent (> 6 months) increase of liver function results for an unknown reason
  • Verification of diagnosis in storage and autoimmune diseases
  • Assessment of the severity of injury in liver cirrhosis or chronic viral hepatitis