01 / Reference ranges
What counts as normal
Normal vs optimal
Many labs print upper limits of 40 U/L or higher, historic ranges built from populations that included undiagnosed fatty liver. The ACG's healthy-population upper limit (33 male, 25 female) is the better yardstick for a screening result; a persistently higher value warrants evaluation even if the report is not flagged.
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02 / Why it matters
What the number tells you
A high ALT most often points at the liver, and the cause the ACG says should be strongly considered at a mild elevation is fatty liver disease, which it says "should be strongly considered in individuals with mild elevations of AST/ALT levels" and which the AGA puts at about 37 percent of US adults. The ACG guideline notes that an elevated ALT is associated with increased liver-related mortality, and that a truly healthy normal is lower than many lab ranges print: 29 to 33 U/L for males and 19 to 25 U/L for females, with levels above that deserving assessment.
03 / In practice
Testing and what moves it
When it is tested
- On a routine comprehensive metabolic panel, or when fatty liver, alcohol, viral hepatitis or a new medication is in question.
- Confirm an unexpected elevation with a repeat test (ACG Recommendation 1); the ACG lists strenuous exercise and muscle injury among non-liver causes, with AST rising more than ALT.
- The evaluation of a persistent elevation (per ACG) covers viral hepatitis, fatty liver, alcohol, medications, iron overload and autoimmune causes.
What raises it
- Fatty liver disease, alcohol, viral hepatitis A/B/C, medications and supplements (acetaminophen in excess, some statin idiosyncrasy, bodybuilding supplements), hemochromatosis.
- Transiently: strenuous exercise, muscle injury.
What lowers it
- Weight loss and treating the underlying cause; ALT falling toward the healthy range is a treatment signal in fatty liver.
- A very low ALT has little clinical meaning.
04 / Related
Read next
Frequently asked questions
My lab says ALT under 40 is normal. Why do you print 33?
Lab ranges were historically built from populations that included people with undiagnosed fatty liver. The ACG guideline states a true healthy normal ALT is 29 to 33 U/L for males and 19 to 25 U/L for females, and that levels above this should be assessed.
What is the most common cause of a mildly high ALT?
Fatty liver disease is the cause the ACG says should be strongly considered with a mild elevation, and the AGA puts its prevalence at about 37 percent of US adults and 70 percent of people with type 2 diabetes. Alcohol, medications and viral hepatitis are the other front-line considerations in the ACG evaluation.
Can exercise raise ALT?
Yes. The ACG lists strenuous exercise and muscle injury among the non-liver causes of raised transaminases, with AST affected more than ALT, and names creatine kinase as the screen for a muscle cause. It gives no waiting period; its instruction is to repeat the panel to confirm the result before starting an evaluation.
One document sets the numbers on this page, published in 2017.
We last re-read these sources on . How we verify.