AST ALT Ratio: Calculator, Interpretation & Clinical Meaning
The AST:ALT ratio is one of the most useful calculations in liver medicine. By comparing these two enzymes, doctors can narrow down the cause of liver injury and distinguish alcoholic liver disease from viral hepatitis or fatty liver.
How to Calculate the AST:ALT Ratio
Example: If your AST is 80 and your ALT is 40, your ratio is 2.0.
What Does the Ratio Tell You?
| AST:ALT Ratio | Most Likely Cause |
|---|---|
| < 1.0 | Viral hepatitis, NAFLD, most chronic liver diseases |
| 1.0 – 2.0 | Early alcoholic liver disease, advanced fibrosis, or mixed causes |
| > 2.0 | Alcoholic liver disease or cirrhosis (highly suggestive) |
| > 3.0 | Very specific for alcoholic hepatitis |
Why Is the Ratio Useful?
ALT is found almost exclusively in the liver. AST is found in the liver, heart, muscles, and other tissues. In alcoholic liver disease, a toxic byproduct called acetaldehyde damages mitochondria, which contain large amounts of AST. This causes AST to rise more than ALT, producing a high ratio.
In contrast, viral hepatitis and NAFLD primarily injure the outer part of liver cells where ALT is concentrated. This causes ALT to rise more than AST, producing a low ratio.
Limitations of the Ratio
The AST:ALT ratio is a helpful clue, but it is not perfect. Exceptions include:
- Muscle injury — raises AST more than ALT, mimicking alcoholic liver disease
- Advanced cirrhosis from any cause — can produce a ratio >2 even without alcohol
- Acute viral hepatitis — sometimes shows a transient ratio >1 in very early infection
Using Our AST/ALT Ratio Calculator
Enter your AST and ALT values below to see your ratio and a brief interpretation. This tool is for educational purposes only and does not replace medical advice.
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