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ALT (Alanine Transaminase)vsAST (Aspartate Transaminase)

ALT vs AST Liver Enzymes

Understanding the differences between ALT and AST liver enzymes and what their ratio tells us about liver health.

Aspect
ALT (Alanine Transaminase)
AST (Aspartate Transaminase)
What it measures
Alanine Aminotransferase - an enzyme found primarily in the liver
Aspartate Aminotransferase - an enzyme found in liver, heart, muscle, and other tissues
Liver specificity
Highly liver-specific - elevation almost always indicates liver issue
Less specific - can be elevated from muscle damage, heart problems, or liver issues
Location in liver cells
Found in cytoplasm - released with mild liver cell damage
Found in cytoplasm and mitochondria - released with more severe damage
Typical elevation pattern
Higher than AST in most non-alcoholic liver diseases (ratio <1)
Higher than ALT in alcoholic liver disease and cirrhosis (ratio >2)
Non-liver causes
Few - almost always indicates liver issue
Many - exercise, muscle injury, heart attack, thyroid disease

Key Differences

  • •ALT is more specific to the liver; AST is found in multiple tissues
  • •The AST:ALT ratio helps distinguish alcoholic from non-alcoholic liver disease
  • •ALT is usually higher in fatty liver; AST is usually higher in alcoholic liver disease
  • •AST elevation after intense exercise is common and not liver-related
  • •In cirrhosis, AST often exceeds ALT regardless of cause

Why Both Matter

ALT and AST are both valuable liver enzymes, but they provide different information. ALT is more liver-specific, making it the preferred marker for detecting liver disease. When ALT is elevated, it almost certainly indicates a liver problem.

AST is less specific because it's present in many tissues including heart, muscle, kidneys, and brain. Intense exercise, muscle injury, and even thyroid disease can elevate AST without liver involvement. However, AST provides important information when interpreted alongside ALT.

The AST:ALT ratio is particularly useful for distinguishing between causes of liver disease: - Ratio <1 (ALT higher): Typical of non-alcoholic fatty liver disease (NAFLD), hepatitis - Ratio >2 (AST higher): Suggests alcoholic liver disease - Ratio increases as liver disease progresses to cirrhosis

Additionally, AST contains both cytoplasmic and mitochondrial forms, so very high AST relative to ALT can indicate more severe liver cell damage with mitochondrial involvement.

Testing both enzymes provides a more complete picture of liver health and helps narrow down the likely cause of liver abnormalities.

Learn more about

ALT (Alanine Transaminase)

An enzyme found mainly in the liver.

Learn more about

AST (Aspartate Transaminase)

An enzyme found in the liver, heart, and muscles.

Frequently Asked Questions

Why is my AST elevated but ALT is normal?
AST elevation alone often indicates a non-liver source. Common causes include muscle damage from exercise, muscle disease, heart conditions, or thyroid problems. If only AST is elevated, liver disease is less likely.
What does an AST:ALT ratio over 2 mean?
A ratio >2 strongly suggests alcoholic liver disease. This pattern occurs because alcohol preferentially damages hepatocyte mitochondria, releasing more AST. However, advanced cirrhosis from any cause can also elevate the ratio.
How high do ALT/AST need to be to indicate a problem?
Mild elevation (1-3x normal) is common and often due to fatty liver or medications. Moderate elevation (3-10x) warrants investigation. Severe elevation (>10x) suggests acute hepatitis, toxicity, or ischemia.
Can exercise cause elevated liver enzymes?
Yes, but primarily AST, not ALT. Intense exercise can elevate AST 2-3x normal through muscle damage. If both are elevated after exercise, it's worth retesting after a few days of rest.

Track Both Markers Over Time

Upload your blood test results to BloodTrack and monitor both ALT (Alanine Transaminase) and AST (Aspartate Transaminase). See how they change together over time.

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