AST (Aspartate Aminotransferase) levels, explained
AST is an enzyme found in the liver, heart, and muscles; in routine testing it is used mainly to assess liver health alongside ALT.
What’s a normal AST level?
Typical adult reference range, shown for orientation. Your report’s range may differ by lab, age, and sex — the analyzer uses your report’s own ranges when available.
What high and low AST mean
A value outside the reference range is a flag, not a diagnosis. Here’s what each direction usually points to — and the most common causes.
High AST can reflect liver injury, but because AST also comes from muscle, it can rise after intense exercise, muscle injury, or heart events.
- Liver conditions (fatty liver, hepatitis, alcohol)
- Recent strenuous exercise or muscle injury
- Certain medications and supplements
- Heart muscle injury (in specific contexts)
A low AST is generally not clinically meaningful and rarely requires any action.
- Normal variation
- Occasionally vitamin B6 deficiency
When a AST result needs attention
AST several times above normal, or elevation with jaundice, abdominal pain, or symptoms suggesting a cardiac cause, should be evaluated without delay.
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AST (Aspartate Aminotransferase) — frequently asked questions
- What does a high AST mean?
- A high AST often reflects liver irritation, but because AST is also present in muscle and heart tissue, it can rise after hard exercise, muscle injury, or certain cardiac events. It is interpreted alongside ALT — when both are up, the liver is the likely source.
- Does exercise raise AST?
- Yes. Intense or unaccustomed exercise can release AST from muscle and temporarily raise the blood level without any liver problem. If your AST is up after a hard workout, retesting after a few days of rest often clarifies the picture.
- What is a normal AST level?
- Typical adult reference ranges run roughly 8–48 U/L, though labs differ. AST is best read together with ALT and the rest of the liver panel rather than as a standalone number.
Related lab markers
- ALT (Alanine Aminotransferase) →ALT is a liver enzyme released into the blood when liver cells are stressed or damaged — one of the most sensitive markers of liver health.
- Creatinine →Creatinine is a muscle waste product cleared by the kidneys — the standard blood marker used to estimate kidney function.
- Ferritin →Ferritin is the protein that stores iron in your body — it is the single best blood marker of how much iron you have in reserve.
- All lab markers →Browse every biomarker guide in one place.
This page provides educational health information and does not replace professional medical advice, diagnosis, or treatment. Interpret any lab value with your clinician, who has your full medical context. For emergencies, contact emergency services.