ALT vs AST - what's the difference?
Both are liver enzymes, but ALT is more specific to the liver, while AST is also in muscle and heart. Here's what their ratio means.
ALT
An enzyme found mostly in the liver. A rise is a more specific signal of liver injury in particular.
AST
An enzyme in the liver, but also in muscle and heart. A rise is less specific - it can come from muscle or exercise too.
ALT vs AST
| Alanine Aminotransferase (ALT) | Aspartate Aminotransferase (AST) | |
|---|---|---|
| Unit | U/L | U/L |
| Typical adult range | 7–40 U/L | 8–33 U/L |
| Common reasons for a high value | Non-alcoholic fatty liver disease (NAFLD); Viral hepatitis | Liver injury; AST/ALT ratio > 2 |
| Common reasons for a low value | Vitamin B6 deficiency; Severe end-stage liver disease | Vitamin B6 deficiency; Severe end-stage liver disease |
Key differences
- ALT is more liver-specific; AST is also in muscle/heart.
- The AST/ALT ratio helps a doctor's differential diagnosis.
- Both are part of the liver panel.
- Hard exercise the day before can raise AST more.
What does the AST/ALT ratio mean?
An AST/ALT ratio above 2:1 (the De Ritis ratio) is a classic pointer toward alcohol-related liver disease. It supports a diagnosis rather than making one: a doctor reads it together with the rest of the results.
Source: De Ritis ratio as diagnostic marker of alcoholic liver disease (PubMed 16827089)
Bottom line
ALT is the "liver" enzyme, AST the more general one. Their levels and ratio are read together with the rest of the liver panel, by your doctor.
Frequently asked questions
What does the AST/ALT ratio mean?
It helps distinguish causes (e.g. >2 in certain conditions). Your doctor interprets it in context.
Can AST rise without liver disease?
Yes - intense exercise or muscle injury raise AST. That's why context matters.
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