On This Page – Quick Medical Summary
Your AST result and the range printed beside it
There is no single AST normal range. Each lab prints its own, and the range on your report is the one that applies to your result. Cleveland Clinic describes 8–33 U/L as one common range, while Mayo Clinic Laboratories lists 8–48 U/L for males and 8–43 U/L for females aged 14 and older.
Start where you are:
- AST flagged high: read the sections on reading your report and on results outside the range, then see our guide to next steps for high liver enzymes.
- AST flagged low: go to the section on results outside the range.
- Comparing numbers from other sites: the section on why labs differ explains it.
ℹ️ Medical Disclaimer: This article explains lab reference ranges for general education. It does not diagnose liver or other disease, advise starting, stopping or changing any medication, or replace your clinician’s reading of your results, procedures or insurance coverage. Review your result with the clinician who ordered it, your primary care physician, or a gastroenterologist before acting. For severe or sudden symptoms, call emergency services.
What is a normal AST level on a blood test?
AST normal range varies by laboratory; one common reference range is 8 to 33 U/L (units per liter), according to Cleveland Clinic.
What AST is and where it comes from
Aspartate aminotransferase (AST) is an enzyme found mainly in the liver, and also in the heart, muscles and other tissues, as MedlinePlus explains for the AST test.
🔬 How It Works: AST stays inside healthy cells. When cells are damaged, they release it into the blood, so a high level signals cell injury but not its cause.
Why AST is read with ALT
ALT is the more liver-specific of the two enzymes, according to Cleveland Clinic. Clinicians usually review both together, often within a liver panel.
Why labs report 8–33 or 10–40 U/L for AST
Labs report different AST ranges because each lab sets its own.
Reference ranges come from healthy groups
A reference range reflects results from large groups of healthy people, according to MedlinePlus. Labs often use different testing methods, so they often print different ranges.
Different methods can mean different ranges
Mayo Clinic Laboratories lists its AST method as a photometric rate assay with pyridoxal-5-phosphate; MedlinePlus says methods differ between labs.
Same test, three published ranges
| Source | Group | AST range (U/L) | Key Clinical Detail |
|---|---|---|---|
| Cleveland Clinic | General (one common range) | 8–33 | Varies by lab |
| Mayo Clinic Laboratories | Males, 14 and older | 8–48 | Age and sex required |
| Mayo Clinic Laboratories | Females, 14 and older | 8–43 | Age and sex required |
Sources: Cleveland Clinic (reviewed November 2021); Mayo Clinic Laboratories AST catalog.
Many consumer pages print 10–40 U/L, but no institution in the sources checked here published it; treat it as commonly published, not official.
📊 Clinical Data Point: About 1 in 20 healthy people have an AST result outside the reference range — Source: Cleveland Clinic AST page (reviewed November 24, 2021).
Does the AST normal range differ for men, women and kids?
Published AST ranges can differ by sex and age, as Mayo Clinic Laboratories’ values show.
Men vs women
For ages 14 and older, Mayo lists 8–48 U/L for males and 8–43 U/L for females.
Children and teens
For ages 1–13, Mayo lists 8–60 U/L for boys and 8–50 U/L for girls, and no range is established under 12 months.
✅ Patient Action: Ask your child’s pediatrician: “Which age-specific range did the lab use for this AST result?”
Other things that move AST
Cleveland Clinic lists age, sex, race and weight as factors; MedlinePlus adds pregnancy, exercise and certain medicines. For the ALT enzyme specifically, see how ALT levels change with age.
How to read the AST range printed on your lab report
With your own report:
- Find the test name, your number and the printed normal range.
- Check whether the lab flagged it normal, high or low.
- Compare only with that lab’s range, not ranges seen online.
- To track trends, use the same lab each time.
Is an AST of 40 normal? It depends on the lab
An AST of 40 U/L falls inside both of Mayo Clinic Laboratories’ adult ranges (8–48 for males, 8–43 for females) but above Cleveland Clinic’s common 8–33.
Keep results comparable over time
MedlinePlus explains how reference ranges are set and why results from different labs can’t be compared directly. A log of each report’s printed range keeps your numbers comparable.
✅ Patient Action: Ask your primary care physician: “Which range was my AST compared against?”
What an AST result outside the range can mean
A result outside the range doesn’t always point to a condition needing treatment, according to MedlinePlus, and low AST levels are usually considered normal.
Reasons AST can be high, and not only the liver
MedlinePlus lists hepatitis, cirrhosis, mononucleosis, heart problems, pancreatitis and alcohol use among causes. Cleveland Clinic adds intense exercise, muscle disease and pregnancy.
Why doctors repeat the test and look at ALT
The American College of Gastroenterology advises repeat testing to confirm a liver result is truly abnormal, in its liver-chemistry guideline. Doctors also compare AST with ALT; see the AST/ALT ratio.
Don’t mix up AST and ALT cut-offs
ACG’s healthy figures of 29–33 IU/L for men and 19–25 IU/L for women apply to ALT, not AST.
✅ Patient Action: Ask your primary care physician, or a gastroenterologist if referred: “Should we repeat this with ALT, and what could explain my AST?”
When an AST result should prompt a call to your doctor
⚠️ Clinical Warning: Cleveland Clinic advises calling your provider for symptoms such as jaundice or belly pain, or for new symptoms if you have a diagnosed liver condition. For severe or sudden symptoms, call emergency services.
Symptoms that go with liver problems
MedlinePlus lists these symptoms of liver damage:
- Yellow skin or eyes (jaundice)
- Dark urine or light-colored stools
- Belly pain or swelling, or swollen ankles and legs
- Nausea, vomiting, lost appetite, fatigue or weakness
Who to call and what to ask
✅ Patient Action: Call the clinician who ordered your test, or your primary care physician, and ask: “Do my symptoms and this AST result need a sooner visit?”
AST normal range: frequently asked questions
1. What is the AST normal range for adults?
The AST normal range varies by lab; Cleveland Clinic cites 8–33 U/L as one common range, and Mayo Clinic Laboratories lists 8–48 for adult males.
2. Why do labs report AST as 8–33 or 10–40 U/L?
Labs use different testing methods, so the AST normal range differs; 10–40 is commonly published, so check the range on your report.
3. Is the AST normal range different for men and women?
In some labs, yes: Mayo Clinic Laboratories’ AST normal range is 8–48 U/L for males and 8–43 for females aged 14 and older.
4. What is a normal AST for a child?
Mayo Clinic Laboratories’ AST normal range is 8–60 U/L for boys and 8–50 for girls aged 1–13. Ask the pediatrician which applies.
5. Is an AST of 40 normal?
It depends on the lab: 40 U/L is inside Mayo Clinic Laboratories’ adult AST normal range but above Cleveland Clinic’s common 8–33.
6. Can a healthy person have an AST outside the normal range?
Yes. Cleveland Clinic says about 1 in 20 healthy people fall outside the AST normal range, so a flagged result isn’t always a problem.
7. Does a high AST always mean liver damage?
No. AST also comes from heart and muscle, and intense exercise or pregnancy can raise it. Ask your clinician what explains your result.
8. Is a low AST normal?
MedlinePlus says low AST levels are usually considered normal, even when a result falls below the AST normal range printed on your report.
9. Can exercise or medicines change AST?
Yes. MedlinePlus lists exercise and certain medicines among factors that affect AST results; tell your clinician everything you take.
10. Should I compare AST results from different labs?
No. Labs use different ranges, so compare AST results only within one lab and against that report’s own AST normal range.
11. When should I call a doctor about an AST result?
Call promptly for symptoms such as jaundice or belly pain, per Cleveland Clinic; ask the clinician who ordered your AST test about anything else.
Your next step with an AST result
Bring your report, with its printed range, to your next visit. Ask which range your result was compared against and whether it should be repeated alongside ALT. Your range, symptoms and trend matter more than one number.
About this content
How this article was put together: researched from recognised health sources, drafted with the help of AI tools, and edited by hand, with sources linked throughout.
Sameer Patel is the founder and editor of My Medicine Advisor. He is not a doctor or medical professional — before starting this site he worked in banking,…
Medical disclaimer
The content on MyMedicineAdvisor is provided for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Health information on this website should not be used to diagnose, treat, cure, or prevent any condition without guidance from a qualified healthcare professional. Always seek the advice of your doctor, physician, or another licensed healthcare provider with any questions you may have regarding a medical condition, symptoms, medications, or treatment decisions.
