ALT Normal Range by Age, Gender & Lab

Understanding your ALT normal range is essential for interpreting blood test results. While most labs list 7–56 U/L as the standard adult range, "normal" varies by age, sex, body weight, and even the laboratory performing the test.

Standard ALT Normal Range

For most healthy adults, the typical ALT reference interval is:

Some laboratories use slightly different cutoffs — for example, 10–40 U/L or 10–49 U/L. Always compare your result to the reference range printed on your specific lab report.

ALT Normal Range by Sex

Men typically have slightly higher normal ALT levels than women, partly due to differences in muscle mass and body size. However, significantly elevated levels in either sex warrant follow-up.

ALT Normal Range by Age

ALT levels can vary across the lifespan:

• Children and adolescents may have slightly higher ALT than adults due to growth
• Young adults (20–40) typically have the lowest ALT levels
• Older adults (65+) may see modest increases related to metabolic changes and medication use

See our detailed ALT levels by age chart

Why Normal Ranges Differ Between Labs

Each laboratory establishes its own reference range based on the equipment and methods it uses. A result of 55 U/L might be flagged as high at one lab and normal at another. That is why it is important not to compare results from different laboratories directly.

Is "Normal" the Same as "Optimal"?

Some hepatologists argue that the upper limit of normal should be lower — around 30 U/L for men and 19 U/L for women — because the current ranges were developed using populations that included people with undiagnosed fatty liver disease. An ALT in the upper end of the "normal" range may still indicate early liver stress for some individuals.