Biomarker guide
ALT (U/L)
ALT (alanine aminotransferase) measures an enzyme concentrated in liver cells that leaks into the blood when those cells are stressed or damaged. It is the most liver-specific of the standard enzymes, and people test it to track liver health, particularly relevant given how common fatty liver has become.
Reference ranges
Commonly used adult reference ranges. Labs vary in methodology and cutoffs, interpret your results against your lab report's stated ranges and with your doctor.
Commonly used cutoffs place ALT below roughly 30–40 U/L, with slightly lower thresholds often cited for women; recent exercise and alcohol can raise results.
| Zone | Range |
|---|---|
| Optimal | 0–30 U/L |
| Borderline high | 30–50 U/L |
| High | 50–100 U/L |
The importance of ALT
ALT lives mostly inside liver cells, so a rising blood level generally means liver cells are letting the enzyme out, a marker of cellular stress rather than of liver function itself.[1] Mild elevations are extremely common, and today the leading cause in the US is metabolic-associated fatty liver[2], which tracks closely with insulin resistance, triglycerides, and waist circumference.[3]
Plenty of transient factors can bump ALT: intense exercise in the preceding days, alcohol, acetaminophen and many prescription drugs, some supplements, and recent viral illness. Because of this, an isolated mild elevation is typically retested after a few weeks of abstaining from the likely culprits before further workup.[4]
A persistently elevated ALT, even modestly above range, is worth investigating with your doctor rather than watching indefinitely, since early fatty-liver changes are strongly associated with metabolic factors that respond well to weight loss, reduced alcohol, and better glucose control. Falling ALT on repeat testing is one of the more satisfying trends to watch after lifestyle change.
Part of our complete guide to Organ Health Lab Tests — browse every panel and biomarker guide in this hub.
Frequently asked questions
What is a normal ALT level?
Commonly used reference ranges place ALT below roughly 30–40 U/L, and several professional groups suggest tighter cutoffs of about 30 U/L for men and 25 U/L for women. Labs vary meaningfully, so compare your result to the range on your report and to your own prior values.
What causes high ALT?
The most common cause today is metabolic-associated fatty liver, followed by alcohol, medications (including acetaminophen and statins), viral hepatitis, and some supplements. Intense exercise in the days before the draw can also elevate ALT temporarily, since muscle contains small amounts of the enzyme.
Can exercise raise ALT?
Yes, hard resistance training or endurance efforts in the preceding days can raise ALT (and AST more so) without any liver problem. If you train heavily, taking two to three rest days before a liver panel gives a cleaner baseline reading.
How do I lower an elevated ALT?
When the driver is fatty liver, the evidence points to weight loss, even 5–10% of body weight is associated with meaningful ALT improvement, along with reducing alcohol and added sugar and improving insulin sensitivity. Retesting after two to three months shows whether the trend is moving; persistent elevation warrants a fuller workup with your doctor.
References
- [1] Alanine Aminotransferase (ALT) Test — StatPearls, NCBI Bookshelf (NIH)
- [2] Definition & Facts of NAFLD & NASH — NIDDK (NIH)
- [3] The Link between NAFLD and Metabolic Syndrome — Diagnostics
- [4] Liver Function Tests — StatPearls, NCBI Bookshelf (NIH)
Reviewed by
Jason August
Founder & Editorial Lead
Jason August is the founder of Metabolic Markers and its parent company, Advancing Development. He has spent his career building and scaling real-world ventures, including as a founding team member at Build-A-Bear Workshop during its growth from startup to global public company, and since then across capital, real estate, adaptive reuse, and hospitality. He founded Metabolic Markers to make blood-biomarker testing easier to understand and access, and oversees the site’s content and editorial accuracy. Jason is not a medical professional; all content on this site is educational, reviewed for accuracy, and never a substitute for advice from a licensed physician.
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