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What is the normal range for ALT?
Most lab reports list ALT (alanine aminotransferase) as normal up to the mid-30s or 40 U/L. The American College of Gastroenterology (ACG), however, defines a truly healthy ALT as 29–33 U/L for men and 19–25 U/L for women.
- Your report says normal, but you’re above 33 or 25? Go to the “normal but above” section below.
- Your result is flagged high? Start with the warning-signs section.
- You’re checking a child’s result? Skip to children and teens.
What your lab report’s range means
The reference range on your report comes from the lab that ran your sample. MedlinePlus’s ALT test reference lists 4–36 U/L as normal and notes that ranges vary slightly between labs. For the bigger picture, see what your ALT number really tells you.
What “U/L” and “µkat/L” mean
U/L means units per liter. Using MedlinePlus’s conversion, 4–36 U/L equals 0.07–0.60 µkat/L, the unit many labs outside the US use.
ℹ️ Medical Disclaimer: This article explains ALT reference ranges for general education. It does not diagnose liver disease, recommend treatment, medication or procedures, or advise on insurance coverage for testing. Discuss your result with your primary care physician or a board-certified gastroenterologist or hepatologist before acting on it.
Why the old 40 U/L ALT limit was set too high
The traditional 40 U/L upper limit of normal was likely set using groups that included people with undetected liver disease.
How labs set a reference range
🔬 How It Works: A lab measures ALT in apparently healthy people and labels the middle 95% of results “normal.” If that group quietly includes people with fatty liver, their higher values push the upper limit up. American Family Physician noted in 2002 that the 1980s reference groups probably included such people.
The 2002 study that challenged 40
A 2002 Annals of Internal Medicine study on healthy ALT ranges proposed limits of 30 U/L for men and 19 U/L for women. The standard limits at the time were 40 and 30.
📊 Clinical Data Point: The lower limits raised detection of active hepatitis C infection from 55% to 76.3%, while specificity fell from 97.4% to 88.5%. In other words, more true cases were caught, at the cost of more false alarms. Source: Prati et al., Annals of Internal Medicine, July 2002.
Where the 33 and 25 ALT limits come from
The 33 and 25 figures are the upper ends of ranges set in the American College of Gastroenterology’s 2017 guideline on abnormal liver chemistries.
What the ACG guideline says
The guideline, written by Drs. Kwo, Cohen and Lim in the American Journal of Gastroenterology, defines a healthy ALT level as 29–33 U/L for men and 19–25 U/L for women. It advises doctors to assess levels above these ranges. The authors based the limits on studies from the US, Europe and Asia that linked higher ALT to higher liver-related mortality.
Four definitions of normal, side by side
| Source | Men / boys | Women / girls | Key Clinical Detail |
|---|---|---|---|
| Typical lab range (MedlinePlus) | 4–36 U/L | 4–36 U/L | Varies by lab; what most reports print |
| Prati et al., 2002 | 30 U/L | 19 U/L | Derived from healthy blood donors |
| ACG guideline, 2017 | 29–33 U/L | 19–25 U/L | Levels above should be assessed |
| SAFETY study (children) | 25.8 U/L | 22.1 U/L | 95th percentile in healthy children |
Sources: MedlinePlus (reviewed January 2025); Annals of Internal Medicine (2002); American Journal of Gastroenterology (2017); SAFETY study (NHANES-based).
My ALT is ‘normal’ on my report but above 33 or 25
A result between the ACG limit and your lab’s limit is a reason to have a conversation with your doctor, not a diagnosis.
Why one reading isn’t a diagnosis
The ACG recommends repeating the test, or running a clarifying test, to confirm a result is truly abnormal before a full workup. The guideline also notes that labs use different ALT limits, and that a normal ALT does not rule out significant liver disease. Doctors usually read ALT alongside AST and the other liver markers on a metabolic panel.
Factors that raise ALT, like body weight
The ACG guideline describes a linear relationship between ALT and body mass index: as BMI rises, ALT tends to rise with it. If you don’t know your BMI, you can check it with our free BMI calculator.
Questions to ask your doctor
✅ Patient Action: Ask your primary care physician: “My ALT is above the ACG healthy range. Should we repeat it, and do my BMI or my other liver results change what we check next?”
Why many labs haven’t lowered their ALT limits
The lower limits are debated because they would label a large share of adults as abnormal.
How many people would be flagged
The ACG guideline reports that applying cutoffs of 29 U/L (men) and 22 U/L (women) to national survey data (NHANES) would classify 36% of men and 28% of women as elevated. In one study of 235 workers without symptoms, 27% had abnormal results under lower limits, but only six were found to have liver disease. That study did not track long-term mortality, so it can’t show that the lower limits are wrong.
The overdiagnosis concern
A Chinese laboratory-medicine commentary argued that reference limits are not the same as clinical decision thresholds, and warned that applying the ACG range directly could drive overdiagnosis. Meanwhile, NHANES data from 1988 to 2020 show average adult ALT rose from 15.89 to 21.97 U/L, then eased to 19.19 U/L. The top 5% of results stayed near 49 U/L throughout, so elevated ALT remains common even as the average has improved.
Normal ALT range for children and teens
Children have their own ALT limits, and many hospital ranges sit well above them.
The SAFETY study limits
The SAFETY study of pediatric ALT thresholds looked at healthy-weight, metabolically normal children with no liver disease. Their 95th-percentile ALT level was 25.8 U/L for boys and 22.1 U/L for girls.
Why hospital ranges run higher
The same study found that children’s hospitals used a median upper limit of 53 U/L, with a range of 30 to 90. At those hospital limits, median sensitivity for detecting fatty liver disease, hepatitis B or hepatitis C was 32–48%. The study-derived thresholds raised sensitivity to 72% in boys and 82% in girls.
✅ Patient Action: Ask your child’s pediatrician: “Which ALT upper limit are you using, and would the SAFETY study limits change how you read this result?”
When an ALT result needs prompt medical attention
The ALT number alone rarely signals an emergency. Your symptoms and your other test results matter more.
Warning signs beyond the number
⚠️ Clinical Warning: ACG guidance says acute liver failure needs immediate evaluation, whatever the ALT level. Acute liver failure means rapid liver injury with slowed blood clotting (a prolonged prothrombin time) and confusion (hepatic encephalopathy). Someone with acute hepatitis plus either of those findings needs urgent referral to a liver specialist.
Very high ALT levels
The ACG grades aminotransferase elevations as minimal, mild, moderate or severe, and specifies which grades need immediate evaluation and which allow a more limited workup. For what a raised result can mean, see our guide to a high ALT result.
✅ Patient Action: New confusion alongside an abnormal liver result needs emergency care now. If your ALT is high but you have no symptoms, ask your primary care physician how soon to repeat the test and whether you should see a hepatologist.
Frequently asked questions about the ALT normal range
1. What is a normal ALT level for a woman?
The ACG defines a healthy ALT level for women as 19–25 U/L, though many lab reports list higher upper limits.
2. What is a normal ALT level for a man?
The ACG defines a healthy ALT level for men as 29–33 U/L, below the 40 U/L long used by labs.
3. Is an ALT of 40 normal?
An ALT of 40 falls inside many older lab ranges but sits above the ACG’s healthy ALT limits for both sexes. Ask your primary care physician about retesting.
4. Why does my lab’s ALT normal range differ?
Each lab sets its own ALT reference range, and ACG guidance notes that ALT upper limits vary between laboratories.
5. Is an ALT of 35 bad for a woman?
An ALT of 35 is above the ACG’s healthy limit of 25 for women. That warrants assessment, not an automatic diagnosis; ask your primary care physician about repeating it.
6. Can a normal ALT still mean liver disease?
Yes. The ACG guideline states that a normal ALT level does not exclude significant liver disease. Ask your physician which other tests fit your risk factors.
7. Does weight affect ALT levels?
Yes. The ACG describes a linear relationship between ALT levels and body mass index, so ALT tends to rise as BMI rises.
8. What is a normal ALT range for children?
In the SAFETY study, the 95th-percentile ALT in healthy children was 25.8 U/L for boys and 22.1 U/L for girls.
9. Should I retest a high ALT result?
ACG guidance recommends repeating an abnormal ALT test, or running a clarifying test, before further evaluation. Ask your primary care physician about timing.
10. What ALT level is an emergency?
No single ALT number defines an emergency. ACG guidance says signs of acute liver failure, such as confusion, need immediate evaluation regardless of the ALT level.
11. What is the ALT normal range in µkat/L?
MedlinePlus lists a normal ALT range of 4–36 U/L, equal to 0.07–0.60 µkat/L. Exact ranges vary by lab.
The bottom line on your ALT number
Your ALT result means more once you know which yardstick you’re comparing it against. Your lab’s range tells you whether you fall outside its tested population. The ACG’s 33 and 25 tell you whether you fall outside a truly healthy range. If you land between the two, bring both numbers to your primary care physician.
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
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