AST (Aspartate Aminotransferase) is an enzyme found mostly in your liver, but also in your heart, muscles, and kidneys. Enzymes are proteins that help speed up chemical reactions in the body.
Normally, AST stays inside your cells. But when the liver or muscles are damaged, they spill AST into the bloodstream. This makes an AST blood test a very useful marker for detecting liver injury, though it is almost always evaluated alongside another enzyme called ALT.
Typical AST reference ranges (U/L)
| Adult Men | 10 – 40 | Upper limits vary by lab |
|---|---|---|
| Adult Women | 9 – 32 | Generally slightly lower than men |
Reference ranges for liver enzymes can vary significantly between different laboratories.
What high AST means
A high AST level indicates that cells containing this enzyme have been damaged and are leaking it into the blood. If ALT is also high, the damage is almost certainly in the liver. Common causes of elevated liver enzymes include fatty liver disease, heavy alcohol use, viral hepatitis, or liver-irritating medications (like high doses of acetaminophen/Tylenol).
Because AST is also found in muscles, a high AST with a normal ALT might not be a liver problem at all. It could be caused by an intense workout, a muscle injury, or a heart condition.
The AST/ALT Ratio
Doctors often look at the ratio between AST and ALT to gather clues about what is causing liver stress. In most types of liver disease (like viral hepatitis or fatty liver), ALT is higher than AST. However, in alcoholic liver disease, AST is typically significantly higher than ALT (often a 2:1 ratio).
When to contact your healthcare team
- AST levels in the hundreds or thousands indicate acute, severe liver injury (such as acute viral hepatitis or a toxic reaction to medication) and require immediate medical evaluation.
- Mildly elevated AST (e.g., 50-100 U/L) is very common and often due to fatty liver or alcohol. It is usually monitored over time rather than treated as an emergency.
- If high AST is accompanied by jaundice (yellowing of the eyes or skin), dark urine, or severe abdominal pain, contact a doctor immediately.
Common questions
Can a hard workout raise my AST?
Yes. Because AST is present in skeletal muscle, intense exercise (like heavy weightlifting or a marathon) can cause AST levels to rise temporarily. If you worked out hard before your blood draw, mention it to your doctor.
What does a low AST mean?
A low AST level is generally not a cause for concern and is considered normal.
Related guides
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Medical disclaimer: Educational only; not medical advice, diagnosis, or treatment. AI-generated interpretations are not reviewed by a physician or human clinician. Do not use this content for emergencies; consult a qualified healthcare professional. Do not post personal laboratory results publicly. Reference intervals vary between laboratories—use the value, unit, date and range printed on your own report, and consult a qualified healthcare professional about your results and symptoms.