What is the recommended diagnostic panel for autoimmune hepatitis?

Autoimmune Hepatitis Diagnostic Panel

Initial Serological Testing

The recommended diagnostic panel for autoimmune hepatitis should include antinuclear antibodies (ANA), smooth muscle antibodies (SMA), and serum IgG levels as the first-line tests in adults, with anti-liver kidney microsomal type 1 (anti-LKM1) antibodies added if ANA and SMA are negative. 1

First-Line Autoantibody Panel (Adults)

• ANA and SMA should be tested simultaneously as the initial autoantibody screen in adult patients with suspected AIH 1
• These antibodies should be measured by indirect immunofluorescence at an initial dilution of 1:40 in adults using freshly prepared rodent substrate that includes kidney, liver, and stomach sections 2
• Anti-LKM1 should be assessed after ANA and SMA testing if both are negative, since anti-LKM1 is commonly detected in the absence of ANA and SMA 1
• The diagnostic accuracy for AIH improves from approximately 58% to 74% when two autoantibodies are detected at presentation 1

First-Line Autoantibody Panel (Pediatric Patients)

• In children, ANA, SMA, and anti-LKM1 should all be assessed simultaneously at presentation 1
• Autoantibodies should be tested at an initial dilution of 1:10 in children 2
• Autoantibody titers tend to be lower in children, and the presence of autoantibodies in any titer, combined with other requisite elements, is sufficient to support a definite diagnosis 1

Biochemical Testing

Essential Laboratory Parameters

• Serum aminotransferases (AST and ALT) should be measured, as elevated levels are characteristic of AIH 1
• Serum IgG concentration or total gamma-globulin levels must be assessed, as increased IgG is a diagnostic feature of AIH 1
• Serum alkaline phosphatase (ALP) should be measured to calculate the ALP:AST ratio, which helps distinguish AIH from cholestatic disorders 1

Exclusion Testing

• Viral hepatitis markers (hepatitis A, B, C, E) must be tested to exclude viral etiologies 1
• Drug history should be thoroughly evaluated to exclude drug-induced liver injury 1
• Additional testing for Wilson's disease, hereditary hemochromatosis, and metabolic liver diseases should be performed as clinically indicated 1

Second-Line Autoantibody Testing

When to Perform Additional Testing

If ANA, SMA, and anti-LKM1 are all negative but clinical suspicion remains high, additional serological tests should include anti-soluble liver antigen (anti-SLA), atypical perinuclear anti-neutrophil cytoplasmic antibodies (pANCA), and anti-liver cytosol type 1 (anti-LC1) antibodies. 1

Specific Second-Line Markers

• Anti-SLA antibodies have high specificity (99%) for AIH and have been the sole markers in 14%-20% of patients with AIH 1
• Anti-SLA are associated with severe disease and relapse after drug withdrawal 1
• Anti-LC1 antibodies are present in 32% of patients with anti-LKM1 and occur mainly in children with severe liver disease 1
• Atypical pANCA are present in 50%-92% of patients with type 1 AIH but lack diagnostic specificity 1
• Anti-mitochondrial antibodies (AMA) should be tested to exclude primary biliary cholangitis 1

Histological Assessment

Liver Biopsy Requirements

Liver biopsy is essential and should be performed in all suspected cases of AIH unless active contraindications exist, as it provides critical diagnostic and prognostic information that cannot be obtained through serologic testing alone. 3

Key Histological Features to Evaluate

• Interface hepatitis (periportal hepatitis) is the hallmark histological finding 1
• Plasma cell infiltration in the portal tracts supports the diagnosis 1
• Rosetting of liver cells (hepatocyte clusters) is characteristic 1
• The absence of biliary changes (destructive cholangitis, ductopenia) helps distinguish AIH from cholestatic disorders 1

Diagnostic Scoring Systems

Simplified Diagnostic Criteria

The simplified diagnostic criteria are most useful in routine clinical practice and require a score of ≥6 for probable AIH and ≥7 for definite AIH. 1

The simplified system includes:

• Autoantibodies: ANA or SMA ≥1:40 (1 point); ≥1:80 (2 points); or anti-LKM1 ≥1:40 or anti-SLA positive at any titer (2 points) 1
• IgG levels: >upper limit of normal (1 point); >1.1× upper limit of normal (2 points) 1
• Liver histology: Compatible with AIH (1 point); typical of AIH (2 points) 1
• Absence of viral hepatitis: Yes (2 points) 1

Original Revised Scoring System

• The original revised scoring system is more comprehensive and useful in diagnostically challenging cases with atypical features 1
• A pre-treatment score ≥15 indicates definite AIH, while 10-15 indicates probable AIH 1
• A post-treatment score >17 indicates definite AIH, while 12-17 indicates probable AIH 1

AIH Classification

Type 1 AIH

• Characterized by ANA and/or SMA/anti-actin antibodies 1
• Represents approximately 80% of AIH cases 2
• Anti-SLA antibodies are present in 7%-22% of patients with type 1 AIH 1

Type 2 AIH

• Characterized by anti-LKM1 and/or anti-LC1 antibodies 1
• More common in children and represents approximately 20% of AIH cases 2
• Often presents with more severe disease 2

Common Diagnostic Pitfalls

Critical Considerations

• A single low autoantibody titer should never exclude the diagnosis of AIH in adults or children, nor should high titers establish the diagnosis in the absence of other supportive findings 1
• Seronegative individuals (negative for conventional autoantibodies) may be classified as having cryptogenic chronic hepatitis until markers appear later or until unconventional autoantibodies are tested 1
• Anti-LKM1 is often confused with AMA if rodent kidney is used as the sole immunofluorescence substrate, emphasizing the need for proper substrate selection 2
• Autoantibodies do not cause the disease, and their levels do not reflect treatment response, so they do not need to be monitored during therapy 1
• Relying solely on serological markers without histological confirmation is insufficient and can lead to misdiagnosis 3