AST (Aspartate aminotransferase)
Enzyme found in liver AND skeletal muscle. Not liver-specific, context matters. Heavy training raises AST even with a perfectly healthy liver.
TL;DR. Normal adult: ~10-40 U/L. AST is in liver, muscle, heart, kidney, brain, and red cells, not a liver-only marker. Always pair with ALT and the AST/ALT ratio. Rest 48-72 hours before a draw intended to assess liver function to avoid muscle-origin false alarms.
Definition
AST (aspartate aminotransferase, SGOT) is an intracellular transaminase enzyme that catalyzes transfer of the amino group from aspartate to α-ketoglutarate. It is present in cytoplasm and mitochondria across many tissues, liver, skeletal muscle, cardiac muscle, kidney, brain, and red blood cells. When these cells are injured, AST leaks into circulation. Because it's non-specific, interpretation always pairs AST with the liver-specific ALT.
Reference range
| Range (U/L) | Interpretation |
|---|---|
| 10-40 | Normal |
| 40-80 (1-2× ULN) | Mild elevation, common after training; investigate if persistent |
| 80-200 (2-5× ULN) | Moderate elevation, workup indicated |
| 200-1000 (5-25× ULN) | Marked elevation, acute hepatitis, rhabdomyolysis |
| >1000 | Severe, ischemic hepatitis, acetaminophen toxicity, fulminant viral |
Ranges are laboratory- and assay-dependent.
What high AST means
- Hepatic: viral hepatitis (A, B, C, E), alcoholic liver disease, NAFLD/MASLD, drug-induced injury (including 17α-alkylated oral anabolic steroids, acetaminophen, statins), autoimmune hepatitis, ischemic hepatitis, biliary obstruction.
- Muscle: resistance training, eccentric exercise, endurance events, rhabdomyolysis (check CK).
- Cardiac: myocardial infarction, myocarditis.
- Hemolysis: red-cell AST released in vivo or ex vivo (lab artifact from traumatic draw).
- AST/ALT ratio: >1 suggests alcohol, muscle, or cirrhosis; <1 suggests viral or NAFLD; >2 strongly suggests alcohol.
What low AST means
- Rare and usually not clinically significant.
- Severe vitamin B6 (pyridoxine) deficiency, B6 is a cofactor for the assay.
- Chronic kidney disease on hemodialysis.
- No treatment indicated for isolated low AST in a well patient.
When to test
- Any liver-function panel (CMP), AST is always included.
- Before and during 17α-alkylated oral steroid cycles (Anavar, Winstrol, Dianabol, Anadrol).
- Before and during any new hepatically-metabolized medication.
- Any new fatigue, jaundice, RUQ pain, dark urine, or pale stool.
- Any suspected rhabdomyolysis or CK elevation.
Related tests
FAQ
- What is the normal AST range?
- Approximately 10-40 U/L for adults. Ranges vary by assay and lab; some cite slightly higher upper limits for men. Values up to ~3× the upper limit in a trained athlete the day after heavy training are commonly benign muscle-origin elevations, not liver disease, confirm with CK and repeat after rest.
- Why can heavy training raise AST?
- AST is abundant in skeletal muscle. Muscle damage from resistance training, eccentric exercise, long-duration endurance exercise, or rhabdomyolysis releases AST into circulation for 24-72 hours. Heavy lifters who draw blood within 48 hours of a hard session routinely show AST elevations up to 2-3× ULN. Always rest at least 48-72 hours before a draw intended to assess liver function.
- What does high AST mean?
- Hepatic causes: viral hepatitis, alcoholic liver disease, non-alcoholic fatty liver disease (NAFLD/MASLD), drug-induced liver injury (including 17α-alkylated oral anabolic steroids), autoimmune hepatitis, ischemic hepatitis. Non-hepatic causes: skeletal-muscle injury (exercise, rhabdomyolysis), cardiac events (MI, myocarditis), hemolysis. The AST/ALT ratio helps distinguish: >1 suggests alcohol, muscle, or cirrhosis; <1 suggests viral or NAFLD; >2 strongly suggests alcohol.
- What does low AST mean?
- Low AST is rare and usually not clinically significant. It has been associated with severe vitamin B6 (pyridoxine) deficiency, chronic kidney disease on hemodialysis, and rare metabolic disorders. No treatment is needed for an isolated low AST in a well patient.
- How should I prepare for an AST draw?
- Abstain from heavy exercise for 48-72 hours before the draw to minimize muscle-origin elevation. Avoid alcohol for 3-7 days. Stay hydrated. Inform the lab of any recent injections, injuries, or 17α-alkylated oral steroid use so interpretation accounts for these factors.