From the Guidelines
An elevated AST compared to ALT, often referred to as an AST/ALT ratio greater than 1, typically suggests alcoholic liver disease, but can also be seen in other conditions such as muscle disorders, heart damage, and advanced liver cirrhosis. When evaluating a patient with an elevated AST/ALT ratio, it is essential to consider the clinical context and potential underlying causes. According to a study published in Hepatology 1, an AST/ALT ratio greater than 2 is highly suggestive of alcoholic liver disease (ALD), particularly in patients without cirrhosis. However, other conditions can also cause an elevated AST/ALT ratio, including muscle disorders (myopathies), heart damage (myocardial infarction), certain medications, and advanced liver cirrhosis regardless of cause 1. Some key points to consider when evaluating a patient with an elevated AST/ALT ratio include:
- The patient's medical history, including alcohol consumption and potential exposure to hepatotoxic medications
- The presence of other laboratory abnormalities, such as elevated bilirubin or international normalized ratio (INR)
- The results of imaging studies, such as ultrasound or computed tomography (CT) scans
- The potential for muscle injury or other non-hepatic causes of elevated AST, particularly in patients with a history of intense exercise or statin use 1 Further evaluation may be necessary to determine the underlying cause of an elevated AST/ALT ratio, which may include additional blood tests, imaging studies, and possibly liver biopsy depending on the clinical context. Abstaining from alcohol is crucial if alcoholic liver disease is suspected. It is also important to note that an elevated AST/ALT ratio can be seen in patients with non-alcoholic steatohepatitis (NASH), particularly those with advanced fibrosis or cirrhosis 1.
From the Research
Elevated AST Compared to ALT Levels
- Elevated Aspartate Aminotransferase (AST) compared to Alanine Aminotransferase (ALT) levels can be an indicator of various conditions, including liver damage, muscle injury, and myocardial infarction 2, 3, 4.
- The ratio of AST to ALT (AST:ALT) has been explored as a useful predictor of cirrhosis in patients with chronic hepatitis C infection, with a ratio > or = 1 having high specificity and positive predictive value 5.
- In patients with acute coronary syndrome, elevated AST levels are common, and the AST:ALT ratio can be high, leading to potential exclusions from clinical trials due to suspected liver disease 4.
- The levels of serum aminotransferases, including AST and ALT, can be lower in patients with chronic kidney disease, making it challenging to diagnose liver damage in these patients 6.
Possible Causes
- Chronic alcohol consumption, drugs, non-alcoholic steatohepatitis (NASH), and chronic viral hepatitis can cause elevated AST and ALT levels 2.
- Non-hepatic causes of raised AST and ALT include polymyositis, acute muscle injury, acute myocardial infarction, and hypothyroidism 2, 3, 4.
- The AST:ALT ratio can also be influenced by the grade of fibrosis in patients with chronic hepatitis C infection 5.
Clinical Implications
- The primary care doctor should obtain a complete history regarding risk factors for viral hepatitis, substance abuse, and request investigations accordingly 2.
- Suspected chronic viral hepatitis and liver cirrhosis are best referred to a hepatologist for further management 2.
- The use of AST:ALT ratio as a predictor of cirrhosis should be interpreted with caution, as it may not be diagnostic for the presence of cirrhosis in all patients 5.