What does it mean to have low Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) levels?

Understanding Low AST and ALT Levels

Low AST and ALT levels are generally not clinically significant and do not typically indicate pathology requiring intervention or further workup.

What Are AST and ALT?

AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) are enzymes primarily found in the liver that serve as indirect markers of liver health 1. While AST is also present in cardiac and skeletal muscle and erythrocytes, ALT is more specific to liver tissue 2.

These enzymes are typically measured to detect liver damage rather than to assess for abnormally low levels:

• AST is cleared from plasma at a rate of approximately 1.13 days^-1 3
• ALT is cleared more slowly at approximately 0.47 days^-1 3

Clinical Significance of Low Levels

Low AST and ALT levels are not specifically addressed in clinical guidelines as they are not associated with significant pathology or adverse outcomes. The focus of liver enzyme monitoring in clinical practice is primarily on:

1. Elevated levels indicating potential liver damage
2. Patterns of elevation (hepatocellular, cholestatic, or mixed) 4
3. Ratios between enzymes (such as AST/ALT ratio) for specific diagnostic purposes 1, 5

When AST/ALT Levels Are Clinically Relevant

While low levels aren't concerning, the relationship between these enzymes can provide valuable diagnostic information:

• As liver fibrosis progresses, ALT generally decreases while AST tends to remain stable or increase 1
• An AST/ALT ratio >1 may suggest advancing liver fibrosis 1
• An AST/ALT ratio >2 is highly suggestive of alcoholic liver disease 4, 5
• In cirrhosis, 69% of patients have an AST/ALT ratio ≥2 5

Monitoring Considerations

When monitoring liver enzymes:

• The American Association for the Study of Liver Diseases recommends monitoring liver enzymes every 1-3 months for mild elevations, every 2-3 weeks for moderate elevations, and 2-3 times weekly for severe elevations 4
• After discontinuation of hepatotoxic medications, liver function typically normalizes within 2-7 weeks 4

Key Takeaways

• Low AST and ALT levels are not typically a cause for clinical concern
• The focus in clinical practice is on elevated levels and the pattern/ratio of elevation
• AST/ALT ratio increases as liver fibrosis progresses, making it a useful diagnostic marker for advanced liver disease
• When evaluating liver health, consider the complete liver panel including alkaline phosphatase, GGT, bilirubin, albumin, and prothrombin time/INR 4