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Liver function tests: what do high ALT, AST and GGT mean?
Liver blood tests measure enzymes and proteins that reflect how your liver is working. Mildly raised values are common – here is what they usually mean and which results need prompt attention.
This guide is general information and does not replace medical advice. Reference ranges differ between laboratories – always compare your result with the range printed on your own report and discuss abnormal results with a doctor.
Liver function tests (LFTs) are a group of blood tests. Some, like ALT and AST, are enzymes released when liver cells are damaged; others, like ALP, GGT and bilirubin, reflect the bile ducts; albumin shows how well the liver makes proteins. The pattern of results is often more informative than any single number.
Typical adult ranges
Liver test ranges vary more between laboratories than most other tests. Use the range printed on your report; the values below are typical examples.
| Test | What it shows | Typical upper limit / range |
|---|---|---|
| ALT (GPT, ALAT) | Liver cell damage – the most liver-specific enzyme | up to about 40 U/L (men), 35 U/L (women) |
| AST (GOT, ASAT) | Liver and muscle cell damage | up to about 40 U/L |
| GGT (gamma-GT) | Bile ducts, alcohol, some medicines | up to about 60 U/L (men), 40 U/L (women) |
| ALP | Bile ducts and bone | about 30–130 U/L |
| Bilirubin | Breakdown product of red cells, cleared by the liver | below 21 µmol/L (about 1.2 mg/dL) |
| Albumin | Protein made by the liver | 35–50 g/L |
Most common causes of high liver values
- Fatty liver disease (MASLD, formerly NAFLD) – the most common cause in Europe, linked to excess weight, type 2 diabetes and high triglycerides. ALT is usually higher than AST.
- Alcohol – typically raises GGT; an AST:ALT ratio above 2 suggests alcohol-related liver damage.
- Medicines and supplements – statins, antibiotics, high-dose paracetamol, herbal and bodybuilding products.
- Viral hepatitis (B, C, rarely A or E) – can cause very high ALT in the acute phase.
- Bile duct problems – gallstones or narrowing of the bile ducts raise ALP, GGT and bilirubin.
- Other causes – muscle injury or hard exercise (AST), coeliac disease, thyroid disorders, haemochromatosis and autoimmune liver disease.
A raised ALP with a normal GGT usually comes from bone rather than the liver – for example in growing teenagers, after a fracture or with vitamin D deficiency. A slightly raised bilirubin with otherwise normal tests is often Gilbert's syndrome, a harmless inherited condition.
How high is too high?
- Below 2–3 times the upper limit – common; repeat the test and look for a cause (weight, alcohol, medicines, hepatitis screening).
- 3–10 times the upper limit – needs medical assessment soon.
- More than 10 times the upper limit, or any rise with jaundice – needs urgent assessment.
When should you see a doctor?
See a doctor about any persistently abnormal liver test. Seek urgent care if you notice yellow skin or eyes, dark urine with pale stools, severe abdominal pain, vomiting blood, confusion or marked drowsiness.
Sources
- Newsome PN et al. Guidelines on the management of abnormal liver blood tests (BSG). Gut 2018;67:6–19.
- Kwo PY et al. ACG Clinical Guideline: Evaluation of abnormal liver chemistries. Am J Gastroenterol 2017;112:18–35.
- NHS – Liver function tests and Non-alcoholic fatty liver disease: nhs.uk
- British Liver Trust – Liver blood tests: britishlivertrust.org.uk
Frequently asked questions
Are slightly high liver enzymes serious?
Often not. A mild rise (less than about two to three times the upper limit) is common and is most often caused by fatty liver, alcohol, medicines or recent exercise. It should still be rechecked and the cause looked for, because some conditions are silent.
Can exercise raise ALT and AST?
Yes. Strenuous exercise, especially weight training, releases AST and to a lesser extent ALT from muscles. Avoid hard training for a few days before a repeat test.
Which medicines can raise liver values?
Many – for example statins, some antibiotics, anti-epileptic drugs, methotrexate, high doses of paracetamol and some herbal and bodybuilding supplements. Do not stop a prescribed medicine on your own; discuss it with your doctor.