From the Guidelines
Elevated Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) levels are indicative of liver damage or injury, and it is crucial to determine the underlying cause to guide appropriate treatment and management. These enzymes are normally found inside liver cells, and when the liver is damaged, they leak into the bloodstream, causing their levels to rise in blood tests 1. The severity of elevation can be classified as mild (<5 times the upper reference limit), moderate (5 to 10 times the upper reference limit), or severe (>10 times the upper reference limit) 1. Common causes of elevated AST and ALT levels include:
- Viral hepatitis
- Alcohol consumption
- Fatty liver disease
- Certain medications
- Autoimmune liver conditions The ratio of AST to ALT can provide clues about the underlying cause - for example, alcoholic liver disease typically shows an AST:ALT ratio greater than 2:1, while viral hepatitis often shows a ratio less than 1 1. It is essential to avoid alcohol, review medications with your doctor, and follow up with additional testing, which may include ultrasound, further blood tests, or in some cases, liver biopsy to determine the exact cause and appropriate treatment. The most common causes of fatty liver disease are nonalcoholic fatty liver disease (NAFLD) and alcohol-induced steatosis/steatohepatitis, with NAFLD being the most common liver disease in first-world countries, affecting 20% to 30% of the general population 1.
From the Research
Elevated AST and ALT Levels
Elevated Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) levels are commonly used biomarkers for liver damage 2, 3, 4, 5, 6.
- AST is present in cardiac and skeletal muscle and in erythrocytes, making ALT the most specific marker for liver damage 2.
- Elevated serum ALT levels indicate a high specificity and a reasonable sensitivity for liver injury 4.
- ALT values are increased in the majority but not all patients with acute and chronic liver disease 4.
Causes of Elevated AST and ALT Levels
The causes of elevated AST and ALT levels include:
- Chronic alcohol consumption
- Drugs
- Non-alcoholic steatohepatitis (NASH)
- Chronic viral hepatitis 6
- Non-hepatic causes such as polymyositis, acute muscle injury, acute myocardial infarction, and hypothyroidism 6
Clinical Utility of AST and ALT
Both AST and ALT are useful markers for chronic hepatitis C (CHC) 5.
- The AST/ALT ratio increases with liver histological progression and an AST/ALT ratio ≥1 is highly suggestive of the presence of cirrhosis 5.
- Measuring AST may be useful when the ALT is consistently normal 5.
Diagnostic Approach
In the primary care setting, the doctor should obtain a complete history regarding the risk factors for viral hepatitis, substance abuse, and request investigations accordingly 6.
- Suspected chronic viral hepatitis and liver cirrhosis are best referred to a hepatologist for further management 6.