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ALT: What This Enzyme Reveals About Liver Stress
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What is it?
Alanine aminotransferase, usually called ALT, is an enzyme found mostly in the liver. Small amounts are also found in other parts of the body, including the kidneys and heart.
ALT is one of the main blood markers we use to understand liver health. When liver cells are irritated, inflamed, or injured, ALT can leak into the bloodstream and show up at higher levels on a blood test.
Why it matters
ALT helps show whether the liver may be under stress.
A mildly elevated ALT is often linked to fatty liver, insulin resistance, excess weight, high triglycerides, alcohol intake, or certain medications. Higher ALT levels can sometimes happen with more active liver inflammation or injury, such as viral hepatitis, medication-related liver stress, or significant alcohol-related damage.
ALT is especially useful when tracked over time. A value that is slowly rising may suggest increasing liver strain, even if it is still close to the reference range.
Reference ranges
Healthy ALT levels tend to be slightly lower in females than in males.
ALT levels above these ranges do not diagnose a specific condition on their own, but they can be a sign that the liver is under extra stress. This is more likely when ALT is elevated alongside factors such as excess weight, insulin resistance, high triglycerides, type 2 diabetes, alcohol use, viral hepatitis risk, or medication exposures.
Very high ALT levels are more often seen with more sudden or significant liver injury. ALT should always be interpreted alongside other liver markers, health history, medications, alcohol intake, metabolic risk factors, and trends over time.
Kunutsor, S. K., Apekey, T. A., Seddoh, D., & Walley, J. (2014). Liver enzymes and risk of all-cause mortality in general populations: a systematic review and meta-analysis. International Journal of Epidemiology, 43(1), 187–201.
Kwo, P. Y., Cohen, S. M., & Lim, J. K. (2017). ACG clinical guideline: Evaluation of abnormal liver chemistries. The American Journal of Gastroenterology, 112(1), 18–35.
Moriles, K. E., Zubair, M., & Azer, S. A. (2025). Alanine aminotransferase (ALT) test. In StatPearls. StatPearls Publishing.
Targher, G., Valenti, L., & Byrne, C. D. (2025). Metabolic dysfunction-associated steatotic liver disease. The New England Journal of Medicine, 393(7), 683–698.
This information is educational and does not replace medical advice, diagnosis, or treatment. Your results should be interpreted with a qualified healthcare professional in the context of your health history.
