ALT vs AST: What Is the Difference?
ALT and AST are both liver enzymes, but they tell different stories. Understanding the ALT vs AST distinction helps doctors pinpoint the cause of elevated liver enzymes and guide further testing.
What Is ALT?
ALT (alanine aminotransferase) is found primarily in the liver. It is the most specific blood test for liver cell damage. When ALT rises, it strongly suggests a liver-related problem.
What Is AST?
AST (aspartate aminotransferase) is found in the liver, heart, skeletal muscles, kidneys, brain, and red blood cells. Because it is distributed throughout the body, elevated AST is less specific to the liver than ALT.
Key Differences
| Feature | ALT | AST |
|---|---|---|
| Full name | Alanine aminotransferase | Aspartate aminotransferase |
| Primary location | Liver | Liver, heart, muscle |
| Specificity for liver | High | Moderate |
| Rises first in liver injury | Yes | Sometimes |
| Rises with heart attack | No | Yes |
| Rises with muscle injury | Slightly | Yes |
The AST/ALT Ratio
Doctors often calculate the AST:ALT ratio to narrow down the cause of enzyme elevation:
- Ratio < 1 — typical of viral hepatitis, NAFLD, and most chronic liver diseases
- Ratio > 2 — strongly suggests alcoholic liver disease
- Ratio > 3 — even more specific for alcoholic hepatitis or cirrhosis
- Both very high — may indicate acute hepatitis, drug toxicity, or ischemic liver injury
Use our AST/ALT ratio calculator
Which Test Should You Get?
If you are screening for liver disease, ALT is the better standalone test because it is more liver-specific. However, ordering both ALT and AST together provides more diagnostic information and allows your doctor to calculate the ratio. A full liver function panel includes both enzymes plus ALP, bilirubin, and albumin for the most complete picture.
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