Liver function tests are used to detect liver damage or disease. Combinations of up to five tests are measured at the same time on a blood sample. These are selected from:

• Alanine aminotransferase (ALT) – an enzyme mainly found in the liver; the best test for detecting hepatitis
• Alkaline phosphatase (ALP) – an enzyme related to the bile ducts; often increased when they are blocked
• Aspartate aminotransferase (AST) – an enzyme found in the liver and a few other places, particularly the heart and other muscles in the body
• Total bilirubin – measures all the yellow bilirubin pigment in the blood. Another test, direct bilirubin, measures a form made in the liver and is often requested with total bilirubin in infants with jaundice.
• Albumin – measures the main protein made by the liver and tells how well the liver is making this protein
• Gamma-glutamyl transferase (GGT) - an enzyme found mainly in the liver and is a useful marker for detecting bile duct problems
• Total protein - measures albumin and all other proteins in blood, including antibodies made to help fight off infections

Other tests that can be used to assess liver function include a coagulation screen, together with bilirubin and urobilinogen in urine

When are these tests requested?
These tests are used when symptoms suspicious of a liver condition are noticed. These include: jaundice, dark urine and light-coloured bowel movements; nausea, vomiting and diarrhoea; loss of appetite; vomiting of blood; bloody or black bowel movements; swelling or pain in the belly; unusual weight change; or fatigue or loss of stamina. One or more of these tests may be requested when a person has been or may have been exposed to a hepatitis virus; has a family history of liver disease; has excessive alcohol intake; or is taking a drug that can cause liver damage.

Related websites
RCPA Manual
Australian Hepatitis Council