Blood WorkAST (aspartate aminotransferase) is an enzyme found in the liver, muscles, heart and red blood cells. It's part of a comprehensive metabolic panel (CMP), and many labs use a range of about 8 to 33 U/L. High AST most often comes from fatty liver, alcohol or medicines, but because it's also in muscle, a hard workout can raise it too. Clinicians read it with ALT.
What does AST measure?
AST is an enzyme inside cells of the liver, muscles, heart and red blood cells. When those cells are injured, AST leaks into the blood. Because it isn't specific to the liver, it's always read with ALT, which is mostly in the liver.
What is a normal AST?
| Result | What it usually means |
|---|---|
| About 8 to 33 U/L | Typical range on many lab reports. |
| Mildly high | Fatty liver, alcohol, medicines, or recent hard exercise. |
| Very high (often over 1,000 U/L) | Acute liver injury or poor blood flow to the liver. Needs same-day care. |
Your lab's printed range applies.
What causes high AST?
- Liver causes: fatty liver, alcohol, medicines and supplements, and viral hepatitis.
- Muscle: hard exercise, muscle injury, or muscle problems from some medicines such as statins.
- Red cell breakdown, including a sample damaged during the draw.
- Less common: thyroid disease, celiac disease and heart injury.
Get care the same day if a high AST comes with yellow skin or eyes or severe belly pain. Go to the ER for dark, cola-colored urine with muscle pain or weakness, especially after hard exercise.
What does the AST to ALT ratio mean?
In most liver conditions, including fatty liver, ALT is higher than AST. An AST at least twice the ALT suggests alcohol-related liver disease, and an AST higher than ALT can also be seen with advanced liver scarring. AST and ALT are also part of the FIB-4 score, which estimates liver scarring. If you have fatty liver or its risk factors, a score of 1.3 or higher usually leads to a liver stiffness scan (some guidelines use 2.0 after age 65).
If your AST is high at Passion Health
A Texas-licensed clinician reviews every result and calls you the same day about anything critical. One result outside the range is common and often harmless; we read it with the rest of your panel, your history and your medicines, and recheck when that's the sensible next step.
We look at ALT, recent exercise, alcohol, medicines and supplements, check hepatitis B and C if needed, and calculate FIB-4. If muscle is the likely source, a CK (creatine kinase) test helps. See fatty liver care for the next steps on fatty liver.
AST test cost in Texas
Self-pay. AST comes with every comprehensive metabolic panel. In Essential Blood Work ($59) it's part of 33 results with the draw and a clinician's review included; on its own, the metabolic panel is $20 plus the $29 draw and review fee ($49).
With insurance. If we're in network with your plan, we bill it when the test is covered. You pay cash for a test only after we tell you the price in writing, and Medicare patients sign an Advance Beneficiary Notice first.
AST blood test questions
What is AST in a blood test?
AST, aspartate aminotransferase, is an enzyme found in the liver, muscles, heart and red blood cells. A high level means cells in one of those places are injured. It's part of a comprehensive metabolic panel.
What causes high AST but normal ALT?
Often muscle: a hard workout, injury or a medicine affecting muscle. A damaged blood sample can do it too. Alcohol can also raise AST more than ALT.
What is a normal AST level?
Many labs use about 8 to 33 U/L, but ranges vary. Your clinician reads AST with ALT and your other results.
Is high AST always the liver?
No. AST is also in muscle, heart and red blood cells, so exercise, muscle injury and a damaged sample can raise it. ALT, which is mostly in the liver, helps tell them apart.
Should I avoid exercise before an AST test?
Yes. Avoid unusually hard workouts for a few days before a liver test. Heavy or new exercise, especially weightlifting, can raise AST for up to a week.
Sources
- ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries, American Journal of Gastroenterology, 2017
- AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease, Hepatology, 2023
- MedlinePlus: Aspartate aminotransferase (AST) blood test
- MedlinePlus: Liver Function Tests