How is autoimmune hepatitis diagnosed?

Testing for Autoimmune Hepatitis

The diagnosis of autoimmune hepatitis requires a three-pronged approach: serological testing for specific autoantibodies, biochemical assessment showing elevated aminotransferases and IgG, and liver biopsy demonstrating interface hepatitis, with all three components being essential and none alone being sufficient for diagnosis. 1

Initial Serological Testing Algorithm

Begin with the following autoantibody panel by indirect immunofluorescence on rodent tissue sections: 1

• Antinuclear antibodies (ANA) - present in 80% of North American adults with type 1 AIH 2
• Smooth muscle antibodies (SMA) - present in 63% of type 1 AIH patients 2
• Anti-liver kidney microsome type 1 (anti-LKM1) - characterizes type 2 AIH, present in 3% of North American adults but more frequent in European patients 2
• Anti-liver cytosol type 1 (anti-LC1) - present in 30% of type 2 AIH cases 2

Diagnostic thresholds: 1

• Definite AIH: ANA, SMA, or anti-LKM1 titers ≥1:80 in adults (≥1:20 in children)
• Probable AIH: Titers ≥1:40 in adults

Critical caveat: ANA and/or SMA are present together in 96% of type 1 AIH, and detecting two autoantibodies concurrently improves diagnostic accuracy from 58% to 74%. 2

Supplemental Serological Testing

If conventional autoantibodies are negative but clinical suspicion remains high, proceed with: 1

• Anti-soluble liver antigen/liver pancreas (anti-SLA/LP) - 99% specific for AIH, present in 7-22% of type 1 AIH, and can be the sole marker in 14-20% of cases 2
• Atypical perinuclear anti-neutrophil cytoplasmic antibodies (pANCA) - present in 50-92% of type 1 AIH and can be the only marker when conventional antibodies are negative 2
• Anti-F-actin - a subtype of SMA with high specificity 1, 3
• Anti-LKM3 - for additional type 2 AIH characterization 1

Important pitfall: Anti-LKM1 can be confused with antimitochondrial antibodies (AMA) if rodent kidney is the sole substrate, and can occur in 5-10% of chronic hepatitis C patients, making viral hepatitis exclusion crucial. 2

Biochemical Assessment

Measure the following laboratory parameters: 1, 3

• Serum aminotransferases (ALT/AST) - typically elevated from just above normal to >50 times normal 3
• Total IgG or γ-globulin - elevated >1.5 times upper normal limit for definite diagnosis, any elevation for probable diagnosis 1
• Alkaline phosphatase (ALP) to AST ratio - typically <1.5 in AIH (ratio >3 argues against AIH) 3, 2
• Bilirubin, albumin, and prothrombin time - to assess disease severity 1

Critical limitation: IgG is normal in approximately 10% of European patients and 25-39% of acute presentations in Japanese studies, so normal IgG does not exclude AIH. 2

Liver Biopsy Requirements

Liver biopsy is mandatory and cannot be omitted except in highly typical acute presentations. 2 The biopsy serves three essential purposes: 1

1. Confirms diagnosis by demonstrating interface hepatitis (the histologic hallmark)
2. Evaluates disease severity to determine treatment urgency
3. Stages fibrosis to assess for cirrhosis

Characteristic histological features: 1, 3

• Interface hepatitis - portal inflammation disrupting the limiting plate and extending into the acinus (required finding) 1
• Portal lymphocytic/lymphoplasmacytic infiltrates - typical but not pathognomonic 3, 2
• Plasma cell infiltration - characteristic but neither required nor specific 1
• Hepatocyte rosettes - may be present 2

Exclusionary findings: Ductopenia, destructive cholangitis, well-defined granulomas, or prominent steatosis suggest alternative diagnoses. 1

Mandatory Exclusions Before Diagnosis

The following conditions must be systematically excluded: 1, 2

Viral Hepatitis

• Hepatitis A, B, C, and E serological markers 1

Hereditary/Metabolic Diseases

• Wilson disease - serum ceruloplasmin, 24-hour urinary copper, slit-lamp examination 1
• Genetic hemochromatosis - serum iron, ferritin, transferrin saturation 1
• Alpha-1 antitrypsin deficiency - alpha-1 antitrypsin phenotype 1

Drug-Induced Liver Injury

• Detailed medication history including minocycline, nitrofurantoin, isoniazid, propylthiouracil, methyldopa 1

Alcohol-Related Liver Disease

• Daily alcohol consumption <25 g/day for definite diagnosis, <50 g/day for probable diagnosis 1

Other Autoimmune Liver Diseases

• Primary biliary cholangitis - test for AMA and PDH-E2 antibodies 1
• Primary sclerosing cholangitis - imaging studies, pANCA testing 1

Diagnostic Scoring Systems for Atypical Cases

When clinical, laboratory, serological, or histological features are atypical or sparse, apply diagnostic scoring systems: 1, 3

Revised Original IAIHG Score

Use for diagnostically challenging cases. 1 Incorporates:

• Female sex (supportive feature) 3
• ALP:AST ratio
• Serum IgG or γ-globulin levels
• Autoantibody titers
• Viral markers
• Drug/alcohol exposure
• Liver histology
• Treatment response

Interpretation: 1

• Definite AIH: Pretreatment score ≥15 (sensitivity 95%, specificity 97%)
• Probable AIH: Pretreatment score 10-15 (sensitivity 100%, specificity 73%)

Simplified Scoring System (2008)

Applicable when features are atypical. 3, 2 Includes:

• Autoantibodies (ANA or SMA ≥1:40 = 1 point; ≥1:80 = 2 points; anti-LKM1 ≥1:40 or anti-SLA positive = 2 points)
• IgG levels (>upper normal limit = 1 point; >1.1× upper normal = 2 points)
• Liver histology (compatible = 1 point; typical = 2 points)
• Absence of viral hepatitis (yes = 2 points)

Interpretation: Score ≥6 indicates probable AIH; ≥7 indicates definite AIH (sensitivity and specificity ~90%). 4

Special Clinical Scenarios

Autoantibody-Negative AIH

Approximately 5% of AIH patients are seronegative for conventional autoantibodies. 1 In these cases:

• Test anti-SLA/LP and atypical pANCA 1, 2
• Consider therapeutic trial with corticosteroids if clinical suspicion remains high 4
• If disease responds to treatment but recurs after steroid tapering, AIH diagnosis is confirmed 4

APECED Syndrome

In patients with AIH plus multiple endocrine disorders (hypoparathyroidism, adrenal insufficiency, mucocutaneous candidiasis): 1, 2

• Test for AIRE gene mutations on chromosome 21q22.3
• This is the only AIH syndrome with Mendelian inheritance requiring genetic counseling 1, 2
• Target autoantigens are cytochrome P450 enzymes (CYP1A2, CYP2A6, CYP2D6) 1

Pediatric Considerations

Test ANA, SMA, and anti-LKM1 simultaneously in all pediatric patients (unlike adults where sequential testing is acceptable). 2 Lower autoantibody titers (≥1:20) may be significant in children. 1

Practical Testing Sequence

Follow this algorithmic approach: 1, 2

1. Initial screen: ANA, SMA, anti-LKM1, anti-LC1 by indirect immunofluorescence on rodent tissue
2. If positive: Confirm AIH consideration and proceed to biochemical/histological assessment
3. If negative but suspicion remains: Test anti-SLA/LP, pANCA, anti-F-actin in specialty laboratory
4. Concurrent with serology: Measure IgG/γ-globulin, aminotransferases, ALP, exclude alternative diagnoses
5. Definitive step: Liver biopsy for all suspected cases

Common pitfall: Commercial ELISA-based assays lack standardization and may miss important reactivities. Indirect immunofluorescence on triple tissue (rodent liver, kidney, stomach) remains the reference standard. 5