From the Guidelines
Liver function tests (LFTs) should be interpreted by examining patterns of abnormalities across several biomarkers, including aminotransferases (ALT and AST), alkaline phosphatase (ALP), bilirubin, albumin, and prothrombin time, to assess liver health and function, with consideration of the patient's clinical context, including symptoms, medical history, and risk factors 1. When interpreting LFTs, it's essential to consider the timing, pattern, and magnitude of abnormalities.
- Hepatocellular injury typically shows predominant elevations in ALT and AST, while cholestatic patterns show higher ALP and GGT levels.
- The AST:ALT ratio can provide additional diagnostic clues, with ratios >2 suggesting alcoholic liver disease and ratios <1 more common in viral hepatitis or fatty liver disease.
- Mild elevations (less than 2-3 times normal) may indicate chronic conditions like fatty liver disease, while marked elevations (>10 times normal) suggest acute hepatitis or toxicity. The evaluation of patients with abnormal LFTs should include a detailed history, inventory of medications, and physical examination, with consideration of the patient's risk factors for liver disease, medications, alcohol consumption, comorbid conditions, and signs and symptoms of hepatic disease 1. A comprehensive interpretation of LFTs should prioritize the patient's clinical context and consider the severity of abnormal aminotransferase levels, with mild elevations classified as <5 times the upper reference limit, moderate elevations as 5-10 times the upper reference limit, and severe elevations as >10 times the upper reference limit 1.
From the Research
Interpreting Liver Function Tests
Liver function tests (LFTs) are a crucial diagnostic tool for assessing liver health. The interpretation of these tests requires careful consideration of the clinical context and the specific pattern of abnormalities.
Categories of Liver Function Tests
Liver tests can be categorized into three main groups:
- Tests that assess synthetic function
- Tests that assess hepatocellular necrosis (hepatocellular enzymes)
- Tests that assess cholestasis 2
Clinical Approach to Abnormal Liver Test Results
A systematic approach to evaluating abnormal liver test results is recommended, taking into account the patient's history, physical examination, and laboratory results 3. The pattern and severity of liver injury can provide clues about the underlying cause of the disease.
Pitfalls in Interpreting Liver Function Tests
Several pitfalls can be encountered when interpreting liver function tests, including:
- Normal test results in patients with chronic hepatitis or cirrhosis
- Variations in normal ranges for aminotransferase levels based on sex, ethnicity, and body mass index
- Misdiagnosis of severe alcoholic hepatitis as cholecystitis or cholangitis
- Misdiagnosis of patients with common bile duct stones as having acute hepatitis 4
Evaluation of Abnormal Liver Chemistries
The evaluation of abnormal liver chemistries should include:
- Assessment of hepatocellular injury, including testing for viral hepatitis, nonalcoholic fatty liver disease, and alcoholic liver disease
- Assessment of cholestatic injury, including testing for primary biliary cholangitis and primary sclerosing cholangitis
- Fractionation of total bilirubin to direct and indirect bilirubin fractions to determine the underlying cause of hyperbilirubinemia 5
Key Considerations
- Abnormal liver test results should be interpreted in the context of the patient's clinical history and physical examination
- A stepwise approach to evaluation and management is recommended to optimize high-value care 3
- Liver biopsy may be considered when serologic testing and imaging fail to elucidate a diagnosis or when multiple diagnoses are possible 5