Alanine Aminotransferase (ALT)

What is Alanine Aminotransferase (ALT)?

A liver enzyme measured in blood; ALT rises when liver cells are injured, making it one of the more liver-specific markers of hepatocyte damage.

Alanine aminotransferase (ALT) is an enzyme concentrated mainly in liver cells, so a blood ALT level is often used as a fairly specific signal of liver-cell injury. When hepatocytes are damaged or inflamed, they release ALT into the bloodstream, which is why higher-than-usual ALT is commonly grouped with other liver function tests. Because ALT is found in the liver far more than in other tissues, it is frequently interpreted alongside AST to help distinguish liver-related patterns from muscle or heart sources. The amount of ALT in blood does not directly indicate how much of the liver is affected, and levels can shift with factors unrelated to disease such as intense exercise or certain medicines. Interpretation always belongs with a clinician who reviews it in the context of your full panel and history.

Tests often checked alongside this

• AST (aspartate aminotransferase) — compared with ALT to describe the pattern of liver enzyme changes and hint at possible sources
• ALP (alkaline phosphatase) — helps separate liver-cell patterns from bile-duct (cholestatic) patterns
• GGT (gamma-glutamyl transferase) — supports interpretation of ALP and points toward liver or biliary rather than bone origin
• Total bilirubin — reflects the liver's ability to process and clear bile pigment

How this can show up in how you look and feel

• ALT is a blood measurement and does not itself produce symptoms
• Higher ALT can be associated with liver conditions that are sometimes seen with fatigue, nausea, or reduced appetite
• Markedly elevated liver enzymes are sometimes seen alongside jaundice (yellowing of skin or eyes), dark urine, or abdominal discomfort
• Many people with mildly elevated ALT have no noticeable symptoms at all

What can affect this marker

• Alcohol intake and certain prescription or over-the-counter medicines
• Body weight and fat accumulation in the liver
• Recent intense or unaccustomed physical exercise
• Viral or other infections affecting the liver

What to track over time

• Your ALT trend across repeated tests rather than a single reading
• The ratio and pattern between ALT and AST over time
• Alcohol use and any new medications or supplements started
• Body weight changes and related metabolic markers

What to ask your doctor

• Is my ALT result meaningfully outside the reference range, and should it be rechecked?
• Could any of my current medicines or supplements be affecting my ALT?
• Do my ALT and AST together suggest a pattern that needs further testing?
• What lifestyle steps are appropriate for me given my overall liver picture?

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