AST is an enzyme found not only in the liver but also in the heart, muscles and red blood cells. That is why a rise in it is less "liver-specific" than in ALT.
For that reason AST is almost never interpreted alone — only together with ALT and with their ratio in mind.
Reference ranges
Approximate reference for adults (venous blood):
| Men | up to 40 U/L |
| Women | up to 32 U/L |
| AST/ALT ratio | normally around 1 or less |
What an elevated level means
A rise in AST indicates damage to the tissues where it is found:
Liver: fatty liver, hepatitis, alcohol, medications.
Heart: AST rises with myocardial infarction (though troponin is now used for that).
Muscle: intense workouts, injuries, myopathies.
An isolated rise in AST alone (with normal ALT) more often points to muscle or heart rather than the liver.
What a low level means
A low AST usually has no clinical significance. It is sometimes seen with a deficiency of vitamin B6.
How the test is done
Venous blood, fasting, in the morning.
For 2–3 days avoid alcohol and heavy strength training — they raise AST via the liver and muscles respectively.
What affects the value
- Muscles and training — AST is present in muscle, and exercise raises the level.
- Alcohol — a typical cause, especially with a rising AST/ALT ratio.
- Liver — fatty liver, hepatitis, medications.
- Heart — myocardial damage.
- Sample hemolysis — can falsely inflate the result.
Calculate using this marker
Calculators where AST (aspartate aminotransferase) is used directly:
Frequently asked questions
What does it mean if AST is higher than ALT?
An AST/ALT ratio above 1 (especially above 2) is characteristic of alcoholic liver damage and of advanced fibrosis. In ordinary fatty liver the ratio is more often below 1. But this is only a guide — a doctor interprets it.
AST is high but ALT is normal — what is that?
An isolated rise in AST is more often related not to the liver but to muscle (workouts, injury) or the heart. It is worth retesting at rest; if it persists, look for a non-liver cause.
Why is AST in the FIB-4 index?
FIB-4 estimates the risk of liver fibrosis from age, AST, ALT and platelets. In this formula AST reflects the degree of liver tissue damage. You can calculate it in our FIB-4 calculator.