What this marker measures
ALT is considered one of the most specific markers of liver health. It is almost always measured alongside AST; comparing the two values helps narrow down the cause of any elevation.
High or low: what it can mean
High ALT
An elevated ALT suggests the liver may be under some stress or that liver cells have been damaged. Common causes include fatty liver, alcohol use, viral hepatitis, or certain medications. The degree of elevation helps guide further evaluation.
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Low ALT
ALT values below the reference range are generally not clinically significant. Low values can occasionally occur with severe vitamin B6 deficiency.
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Lifestyle considerations
- •Limiting alcohol consumption supports healthy ALT levels
- •Maintaining a healthy weight reduces the risk of fatty liver-related ALT elevation
Frequently asked questions
What is ALT?
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ALT is an enzyme produced mainly in liver cells. Small amounts normally circulate in the blood, but when liver cells are damaged they release more ALT, raising the blood level.
What does ALT measure?
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ALT is considered one of the most specific markers of liver health. It is almost always measured alongside AST; comparing the two values helps narrow down the cause of any elevation.
What does high ALT mean?
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An elevated ALT suggests the liver may be under some stress or that liver cells have been damaged. Common causes include fatty liver, alcohol use, viral hepatitis, or certain medications. The degree of elevation helps guide further evaluation.
What does low ALT mean?
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ALT values below the reference range are generally not clinically significant. Low values can occasionally occur with severe vitamin B6 deficiency.
What supports healthy ALT levels?
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Limiting alcohol consumption supports healthy ALT levels. Maintaining a healthy weight reduces the risk of fatty liver-related ALT elevation
Related biomarkers
Editorial note
LabTestly explains lab markers using plain-English educational content. Reference ranges may vary by laboratory and should be interpreted with a clinician.
Educational content · Editorially reviewed for clarity · Last updated
Common sources used for lab-test education
Not medical advice
This page is for general understanding only and does not replace medical advice from your clinician. Reference ranges can vary by laboratory, age, sex, pregnancy status, medications, and clinical context.