From the Guidelines
Elevated Aspartate Aminotransferase (AST) levels indicate liver damage or disease, while normal AST levels suggest proper liver function. AST is a liver enzyme that helps monitor liver health, and its elevation may be caused by various conditions such as hepatitis, alcoholic liver disease, or medication-induced liver injury 1. Additionally, other conditions like heart attacks, muscle damage, or certain medications can also cause elevated AST levels 1.
Key Points to Consider
- AST normal levels typically range from 5-40 IU/L, indicating proper liver function 1
- Elevated AST levels are often classified as mild, moderate, or severe, depending on the degree of elevation above the upper reference limit 1
- The severity of abnormal aminotransferase can be classified as 1) mild: <5 times the upper reference limit, 2) moderate: 5 to 10 times the upper reference limit, or 3) severe: >10 times the upper reference limit 1
- Other conditions like nonalcoholic fatty liver disease (NAFLD) and alcohol-induced liver disease can also cause elevated AST levels, with the AST:ALT ratio being generally >2 in alcohol-induced fatty liver disease and <1 in metabolic disease-related fatty liver 1
Important Considerations for AST Levels
- If AST is elevated, additional tests like ALT, alkaline phosphatase, and bilirubin are usually needed to determine the cause and severity of potential liver issues 1
- Regular monitoring of AST levels is important for people with liver conditions or those taking medications that could affect liver function 1
- The liver releases AST into the bloodstream when liver cells are damaged, making it a useful biomarker for detecting liver problems before symptoms appear 1
From the Research
Aspartate Aminotransferase (AST) Elevation
- Elevated serum levels of AST usually indicate hepatocellular damage 2
- AST elevation may also be associated with macro-AST (m-AST), a benign condition that may be considered pathologic by clinicians 3, 4
- AST elevation can also be of extrahepatic origin, such as muscle damage 2
- The ratio of AST to ALT (AST/ALT) and the mitochondrial isoenzyme of AST are frequently higher in alcoholic than in non-alcoholic liver diseases 2
Normal Aspartate Aminotransferase (AST) Levels
- Normal AST levels do not necessarily indicate the absence of liver disease, as some liver diseases may not cause significant elevations in AST 5
- ALT is considered a more specific marker for liver damage than AST, as AST is also present in cardiac and skeletal muscle and in erythrocytes 5
Clinical Significance of AST Elevation
- Elevated AST levels are associated with increased mortality from all-cause, liver disease, and liver cancer 6
- Elevated AST levels can also be associated with increased mortality from other causes, such as stroke, respiratory diseases, and injuries 6
- The presence of elevated AST levels can result in a loss of life expectancy by 10 years or more 6
- In patients with isolated AST elevation, a polyethylene glycol (PEG) precipitation test is recommended to diagnose macro-AST 4