Should elevated liver enzymes prompt an ultrasound?

Evaluation of Elevated Liver Enzymes with Ultrasound

Abdominal ultrasound is recommended as a first-line investigation for patients with elevated liver enzymes (AST 73 and ALT 82) to evaluate for underlying causes such as fatty liver disease, biliary obstruction, or other structural abnormalities. 1, 2

Rationale for Ultrasound in Elevated Liver Enzymes

The elevation of AST (73) and ALT (82) represents a mild hepatocellular pattern of injury (<5× upper limit of normal). This pattern warrants a systematic evaluation to determine the underlying cause:

• Ultrasound is non-invasive, widely available, and cost-effective as an initial imaging modality
• It can detect common causes of liver enzyme elevation including:
  • Fatty liver disease (the most common cause in Western countries)
  • Biliary tract abnormalities
  • Hepatomegaly
  • Mass lesions
  • Signs of cirrhosis

Diagnostic Approach

Initial Assessment:

1. Abdominal Ultrasound: Essential first-line investigation 1, 2

   • Can detect hepatic steatosis with 84.8% sensitivity and 93.6% specificity for moderate-to-severe fatty infiltration (>30% by histology) 1
   • Evaluates for biliary obstruction, masses, and other structural abnormalities
   • Assesses liver size, contour, and echogenicity

2. Laboratory Evaluation:

   • Complete liver panel (already started with AST/ALT)
   • Consider additional tests based on clinical suspicion:
     • Viral hepatitis serology (HAV-IgM, HBsAg, HBcIgM, HCV antibody)
     • Autoimmune markers if autoimmune hepatitis is suspected
     • Iron studies if hemochromatosis is suspected
     • Ceruloplasmin if Wilson disease is suspected in younger patients

Interpretation of Ultrasound Findings:

• Normal liver echogenicity: Similar to or slightly higher than normal renal cortex
• Fatty infiltration grading:
  • Mild: Mild diffuse increase in liver echogenicity with clear definition of diaphragm and intrahepatic vessel walls
  • Moderate: Increased liver echogenicity with obscuration of diaphragm and intrahepatic vessel walls
  • Severe: Marked increase in echogenicity with non-visualization of diaphragm and intrahepatic vessels 1

Clinical Considerations

Common Causes of Mild Liver Enzyme Elevation:

• Non-alcoholic fatty liver disease (NAFLD) - most common in Western countries (20-30% prevalence) 1
• Alcohol-related liver disease (AST:ALT ratio typically >2) 2
• Drug-induced liver injury
• Viral hepatitis
• Hemochromatosis

When to Consider Liver Biopsy:

Liver biopsy should be considered in specific situations:

• C282Y homozygotes or compound heterozygotes if liver enzymes are elevated or ferritin >1000 μg/L 1
• Patients with phenotypic markers of iron overload who are not C282Y homozygotes 1
• When non-invasive tests are inconclusive and diagnosis would change management

Management Approach

1. Address underlying causes:

   • Lifestyle modifications for NAFLD (weight loss, exercise, Mediterranean diet)
   • Discontinue suspected hepatotoxic medications
   • Treat specific conditions identified

2. Monitoring:

   • For mild elevations: Follow-up liver enzymes in 1-3 months
   • If persistent or worsening: Consider referral to gastroenterology/hepatology

Pitfalls and Caveats

• Ultrasound has limited sensitivity for mild steatosis (53.3-65%) 1
• Ultrasound cannot reliably distinguish between simple steatosis and non-alcoholic steatohepatitis (NASH)
• Ultrasound assessment is subjective and has inter/intra-observer variability
• Consider calculating FIB-4 score to assess risk of advanced fibrosis in patients with suspected NAFLD 2
• Normal ultrasound does not exclude all liver pathology; clinical correlation is essential

In summary, abdominal ultrasound is an appropriate and recommended first-line investigation for patients with mildly elevated liver enzymes to evaluate for common causes and guide further management decisions.