What liver function tests measure
Liver function tests (LFTs) — also called liver enzymes or a liver panel — are a group of blood tests that measure different proteins and enzymes released by the liver. They assess different aspects of liver health:
ALT (alanine aminotransferase) — enzyme found mainly in liver cells. Rises when liver cells are damaged or inflamed.
AST (aspartate aminotransferase) — enzyme in liver and muscle. Less specific to the liver than ALT.
ALP (alkaline phosphatase) — enzyme in liver, bone, and bile ducts. Elevated in bile duct blockage or bone disorders.
GGT (gamma-glutamyl transferase) — sensitive marker of alcohol use and bile duct problems.
Bilirubin — yellow pigment from broken-down red blood cells, processed by the liver. High levels cause jaundice.
Albumin — protein made by the liver. Low albumin may indicate reduced liver synthetic function.
Together these tests give a picture of liver inflammation, liver cell damage, bile flow, and liver function. No single test tells the whole story.
Why your GP ordered it
LFTs are ordered in many clinical situations:
- Screening for fatty liver disease, particularly in people with obesity, diabetes, or metabolic syndrome
- Investigating symptoms — right upper abdominal pain, jaundice, nausea, or fatigue
- Monitoring medications that can affect the liver — statins, methotrexate, anti-epileptics, some antibiotics
- Assessing alcohol-related liver damage
- Investigating viral hepatitis (hepatitis B or C)
- Routine annual blood tests for chronic disease management
- Pre-operative assessment
What the test involves
LFTs are measured from a standard blood sample. Fasting is not required, though your GP may request fasting if lipids or glucose are being tested at the same time.
Results are usually available within 24 hours. An abnormal LFT result almost always leads to further investigation — the LFT panel is a starting point, not a diagnosis.
Australian laboratory context
In Australia, liver function tests are reported as part of a biochemistry panel. Units vary by test — ALT and AST are reported in U/L (units per litre), bilirubin in µmol/L, albumin in g/L.
Mildly elevated LFTs are extremely common and most often benign — fatty liver (non-alcoholic fatty liver disease, NAFLD) is now the most common cause in Australian adults. Many people with mildly elevated liver enzymes have no symptoms and are not aware of any liver problem.
Reference ranges differ slightly between laboratories and between males and females (particularly for ALT and GGT). Always check the reference range on your specific laboratory report.
Your GP will interpret your results in the context of your full medical history, your symptoms, your medications, and any previous results. A result outside the reference range does not automatically mean something is wrong, and a result within range does not always mean there is no problem. Always discuss your results with your GP or the clinician who ordered the test.