What lab workup is essential for diagnosing autoimmune hepatitis?

Essential Laboratory Workup for Autoimmune Hepatitis

The essential laboratory workup for diagnosing autoimmune hepatitis includes liver biochemistry tests, immunoglobulin levels, autoantibody testing, viral hepatitis markers, and a liver biopsy, which is considered a prerequisite for definitive diagnosis. 1, 2

Core Laboratory Tests

Liver Biochemistry

• Aminotransferases (AST/ALT): Typically elevated, ranging from just above normal to >50 times upper limit
• Alkaline phosphatase (ALP): Usually less elevated than aminotransferases
• ALP:AST (or ALT) ratio: Typically <1.5 in AIH 2
• Bilirubin: Variable elevation

Immunoglobulin Assessment

• Serum IgG or γ-globulin levels: Elevated in approximately 85% of patients 1

  • 1.5 times upper normal limit supports definite AIH

  • Any hypergammaglobulinemia supports probable AIH
  • Note: 25-39% of patients with acute onset may have normal IgG levels 1

Autoantibody Testing

1. Conventional autoantibodies (first-line testing):

   • Antinuclear antibodies (ANA)
   • Smooth muscle antibodies (SMA)
   • Anti-liver/kidney microsome type 1 antibodies (anti-LKM1)
   • Antimitochondrial antibodies (AMA) - to exclude primary biliary cholangitis

2. Supplemental autoantibodies (second-line testing):

   • Anti-soluble liver antigen/liver pancreas (anti-SLA/LP)
   • Anti-liver cytosol type 1 (anti-LC1)
   • Perinuclear anti-neutrophil cytoplasmic antibodies (p-ANNA)

Important technical considerations: Autoantibodies should be tested by indirect immunofluorescence at an initial dilution of 1/40 in adults and 1/10 in children on freshly prepared rodent substrate including kidney, liver, and stomach sections 1, 3

Exclusion of Other Liver Diseases

• Viral hepatitis markers: HAV, HBV, HCV serologies (must be negative)
• Metabolic liver disease tests:
  • α1-antitrypsin phenotype
  • Serum ceruloplasmin and copper levels
  • Iron studies (ferritin, transferrin saturation)
• Alcohol and drug history: To exclude alcohol-related and drug-induced liver injury

Liver Biopsy

• Essential for diagnosis and treatment decisions 1, 2, 4
• Key histological features:
  • Interface hepatitis
  • Dense plasma cell-rich lymphoplasmocytic infiltrates
  • Hepatocellular rosette formation
  • Emperipolesis (active penetration by one cell into and through a larger cell)
  • Absence of biliary lesions, granulomas, or other features suggesting alternative diagnoses

Diagnostic Scoring Systems

Two validated scoring systems can help confirm the diagnosis:

1. Original Revised Scoring System (1999):

   • More comprehensive, research-oriented
   • Pretreatment score ≥15: definite AIH (sensitivity 95%, specificity 97%)
   • Score 10-15: probable AIH

2. Simplified Scoring System (2008):

   • More practical for clinical use
   • ≥7 points: definite AIH (sensitivity 81%, specificity 99%)
   • ≥6 points: probable AIH 2, 5

Additional Considerations

Imaging

• Children: All children with AIH should undergo MR cholangiography to exclude autoimmune sclerosing cholangitis 1
• Cirrhotic patients: Liver ultrasound every 6 months for HCC screening 1

Special Situations

• In patients with AIH and multiple endocrine disorders, consider testing for APECED syndrome (mutations in the AIRE gene) 2
• For seronegative cases, newer tests like polyreactive IgG (pIgG) may be helpful (present in up to 88% of seronegative AIH) 6

Common Pitfalls to Avoid

• Relying solely on autoantibody testing without histological confirmation
• Misinterpreting anti-LKM-1 as anti-mitochondrial antibody when using only kidney substrate 3
• Failing to recognize that normal IgG levels don't exclude AIH, especially in acute presentations
• Not sending samples to reference laboratories in cases of diagnostic uncertainty 1