From the Guidelines
In the evaluation of hepatic encephalopathy, AST, ALT, and GGT are crucial markers of liver dysfunction, with AST and ALT indicating hepatocellular damage and GGT suggesting biliary tract disease or alcohol use. The difference between these enzymes lies in their tissue distribution and specificity: AST is found in multiple tissues, including the liver, heart, and muscle, while ALT is more liver-specific 1. Elevated AST:ALT ratio >2:1 (DeRitis ratio) is suggestive of alcoholic liver disease, a common cause of encephalopathy 1. GGT, on the other hand, is a more sensitive marker for biliary tract disease and alcohol use, rising earlier than other enzymes in alcohol-related liver injury 1. Key points to consider in the evaluation of these enzymes include:
- AST and ALT elevations indicate hepatocellular damage, with ALT being more specific to the liver 1
- GGT elevation suggests biliary tract disease or alcohol use 1
- The pattern of elevation helps determine the underlying cause of encephalopathy, guiding appropriate treatment 1
- Markedly elevated liver enzymes (AST/ALT >1000 IU/L) with encephalopathy suggest acute liver failure requiring urgent intervention, while more modest elevations with an elevated GGT might point to chronic liver disease or alcoholic hepatopathy 1. In encephalopathy workup, these enzymes should be evaluated together rather than in isolation to determine the underlying cause and guide appropriate treatment, which might include lactulose, rifaximin, or addressing the specific liver insult 1.
From the Research
Overview of AST, ALT, and GGT in Hepatic Encephalopathy
- Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), and Gamma-Glutamyl Transferase (GGT) are enzymes measured in serum or plasma to investigate liver disease 2.
- The AST/ALT ratio has been used to noninvasively assess the severity of disease in patients with chronic liver disease (CLD) 3.
- AST, ALT, and GGT measurements are important for the assessment of liver damage 4.
Differences between AST, ALT, and GGT
- AST is found in various tissues throughout the body, including the liver, heart, and muscles, while ALT is primarily found in the liver 5.
- GGT is found in many organs, including the liver, kidneys, and pancreas, and is often used as a marker for liver disease or alcohol use 6.
- The ranges of within-subject variation reported for AST, ALT, and GGT are: AST: 3.0%-32.3%, ALT: 11.1%-58.1%, and GGT: 3.9%-14.5% 2.
Clinical Utility of AST, ALT, and GGT in Hepatic Encephalopathy
- Serum AST, ALT, and LDH may be related to early diagnosis and prognosis in patients with encephalopathy 5.
- The AST/ALT ratio is correlated with both histologic stage and clinical evaluation of liver disease 3.
- GGT is often used as a marker for liver disease or alcohol use, and elevated levels may indicate liver damage or disease 6.
- Common reference intervals for AST, ALT, and GGT in serum have been established, but may vary depending on the population and region 4.