From the Guidelines
Elevated AST levels are primarily caused by liver damage from conditions such as viral hepatitis, alcoholic liver disease, nonalcoholic fatty liver disease, and drug-induced liver injury, as well as muscle damage and other non-hepatic causes. The most recent and highest quality study 1 suggests that hepatocellular injury causes the release of ALT and AST in serum, and that AST levels are also increased in fatty liver disease and cirrhosis. According to this study, common causes of mild increases in aminotransferases are nonalcoholic fatty liver disease (NAFLD) and alcohol-induced liver disease.
Some key points to consider when evaluating elevated AST levels include:
- The AST:ALT ratio can help determine the cause of elevated AST, with alcoholic liver disease typically showing an AST:ALT ratio greater than 2:1 1
- Non-hepatic causes of elevated AST, such as hemolysis, myopathy, thyroid disease, and exercise, should also be considered if the aminotransferase rise is predominantly AST 1
- Medications and toxins can also cause elevated AST levels, and should be considered in the differential diagnosis
- The clinical context and other laboratory results, such as ALT and other liver enzymes, should be taken into account when interpreting elevated AST levels.
It's worth noting that the study from 2023 1 provides more comprehensive and up-to-date information on the causes of elevated AST levels, and should be prioritized over the 2010 study 1 when making clinical decisions.
From the Research
Causes of Elevated AST
- Elevated AST levels can be caused by various factors, including liver damage, cardiac and skeletal muscle damage, and hematologic disorders 2, 3, 4, 5
- Liver damage is a common cause of elevated AST levels, but AST is not as specific a marker for liver damage as alanine aminotransferase (ALT) 2
- Non-hepatic causes of elevated AST levels include skeletal muscle damage, cardiac muscle damage, and hematologic disorders, with skeletal muscle damage being the most common etiology 5
- Macro-enzyme aspartate aminotransferase (macro-AST) is a benign cause of persistently elevated AST levels in the absence of other diseases 6
- The magnitude of the peak AST level can significantly correlate with 30-day mortality, with higher peak AST levels associated with increased mortality 5
Non-Hepatic Causes of Elevated AST
- Skeletal muscle damage is the most common non-hepatic cause of elevated AST levels, accounting for 54.2% of cases 5
- Cardiac muscle damage is another common non-hepatic cause of elevated AST levels, accounting for 39.1% of cases 5
- Hematologic disorders are a less common non-hepatic cause of elevated AST levels, accounting for 6.7% of cases 5