From the Guidelines
Liver function tests (LFTs) should be analyzed by looking at patterns of abnormalities rather than isolated values, prioritizing hepatocellular injury, cholestasis, or mixed patterns, as recommended by the most recent guidelines 1. When analyzing LFTs, it is essential to consider the different enzymes and their implications:
- Hepatocellular injury is indicated by elevated ALT and AST levels, with ALT being more liver-specific than AST 1.
- Cholestasis is characterized by elevated alkaline phosphatase, GGT, and bilirubin levels, which may indicate obstruction or impairment of bile flow 1.
- The AST:ALT ratio can provide valuable information, with a ratio >2 suggesting alcoholic liver disease, although this is not universally accepted 1. Key considerations when interpreting LFT results include:
- Clinical context, including medication history, alcohol use, and risk factors for viral hepatitis 1.
- Serial measurements, which can show progression or improvement, are often more valuable than single readings 1.
- Normal LFTs do not completely exclude liver disease, as conditions like cirrhosis may present with normal enzymes if inactive 1. In terms of specific enzyme levels, mild elevations (less than 2-3 times normal) may indicate fatty liver, while marked elevations (>10 times normal) suggest acute viral hepatitis, drug toxicity, or ischemic injury 1. Bilirubin elevation should be categorized as conjugated or unconjugated to distinguish between hepatic processing issues and hemolysis, and albumin and prothrombin time reflect synthetic function and are important for assessing liver disease severity 1.
From the Research
Analysis of Liver Function Tests (LFTs)
The analysis of LFTs involves evaluating various biochemical parameters, including AST, ALT, GGT, alkaline phosphatase, bilirubin, and albumin levels, as well as coagulation tests such as prothrombin activity 2. These tests are used to:
- Assess synthetic function
- Evaluate hepatocellular necrosis (hepatocellular enzymes)
- Assess cholestasis 3
- Detect and diagnose liver disease
- Estimate the severity of liver disease
- Monitor the efficacy of therapy 4
Interpretation of LFT Results
The interpretation of LFT results requires careful attention to clinical data obtained during history taking and physical examination 3. The results can be categorized into:
- Tests that assess synthetic function (e.g., albumin levels)
- Tests that assess hepatocellular necrosis (e.g., AST, ALT)
- Tests that assess cholestasis (e.g., alkaline phosphatase, GGT) 3
- The pattern of liver test abnormalities can help identify the type and etiology of liver disease, allowing for a targeted investigation approach 5
Evaluation of Abnormal LFT Results
Abnormal LFT results can be caused by various factors, including:
- Hepatocellular injury (e.g., viral hepatitis, alcoholic liver disease)
- Cholestatic injury (e.g., biliary obstruction, primary biliary cirrhosis)
- Other conditions (e.g., hemolysis, ineffective erythropoiesis) 2
- The severity of liver injury is best assessed by composite scores, such as the Model for End Stage Liver Disease, rather than any single parameter 5
Utility of LFTs
LFTs are useful for:
- Screening people for the presence of liver disease
- Suggesting the underlying cause of liver disease
- Estimating the severity of liver disease
- Monitoring the efficacy of therapy 4
- However, the value of screening healthy, asymptomatic persons for liver disease with LFTs is controversial and may not be cost-effective 4