ALT (Alanine Aminotransferase) levels, explained
ALT is a liver enzyme released into the blood when liver cells are stressed or damaged — one of the most sensitive markers of liver health.
What’s a normal ALT level?
Typical adult reference range, shown for orientation. Your report’s range may differ by lab, age, and sex — the analyzer uses your report’s own ranges when available.
What high and low ALT mean
A value outside the reference range is a flag, not a diagnosis. Here’s what each direction usually points to — and the most common causes.
High ALT indicates the liver is irritated or inflamed; the most common cause today is fatty liver disease, but alcohol, medications, and viral hepatitis also raise it.
- Non-alcoholic fatty liver disease (very common)
- Alcohol use
- Medications and supplements (including high-dose acetaminophen)
- Viral hepatitis or other liver conditions
A low ALT is generally not clinically significant and is not usually a cause for concern.
- Normal variation
- Occasionally associated with vitamin B6 deficiency
When a ALT result needs attention
ALT more than ~3 times the upper limit, a rapidly rising ALT, or elevation with jaundice, dark urine, or abdominal pain should be evaluated promptly.
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ALT (Alanine Aminotransferase) — frequently asked questions
- What does a high ALT mean?
- A high ALT means liver cells are leaking this enzyme into the blood because they are inflamed or damaged. The most common cause is fatty liver disease, followed by alcohol, certain medications and supplements, and viral hepatitis. Mild elevations are common; large or rising elevations need evaluation.
- Can high ALT return to normal?
- Often yes. When the cause is reversible — fatty liver, alcohol, or a medication — ALT frequently normalizes after weight loss, reducing alcohol, or stopping the offending drug. Repeat testing after addressing the cause confirms improvement.
- What is the difference between ALT and AST?
- Both are liver enzymes, but ALT is more specific to the liver, while AST also comes from muscle and other tissues. The ratio between them helps point to a cause — for example, an AST higher than ALT can suggest alcohol-related injury, while ALT higher than AST is more typical of fatty liver.
Related lab markers
- AST (Aspartate Aminotransferase) →AST is an enzyme found in the liver, heart, and muscles; in routine testing it is used mainly to assess liver health alongside ALT.
- Creatinine →Creatinine is a muscle waste product cleared by the kidneys — the standard blood marker used to estimate kidney function.
- Ferritin →Ferritin is the protein that stores iron in your body — it is the single best blood marker of how much iron you have in reserve.
- All lab markers →Browse every biomarker guide in one place.
This page provides educational health information and does not replace professional medical advice, diagnosis, or treatment. Interpret any lab value with your clinician, who has your full medical context. For emergencies, contact emergency services.