Diagnostic Autoantibody Testing for Autoimmune Hepatitis
The initial serological battery for diagnosing autoimmune hepatitis must include antinuclear antibodies (ANA), smooth muscle antibodies (SMA), anti-liver/kidney microsome type 1 (anti-LKM1), and anti-liver cytosol type 1 (anti-LC1), tested by indirect immunofluorescence on rodent tissue sections. 1
Primary Autoantibody Panel
Type 1 AIH Markers (75-80% of cases)
- ANA is positive in 75-95% of AIH-1 patients, typically showing homogeneous pattern (2/3 of cases) or speckled/nucleolar pattern (1/3) on HEp-2 cells 1, 2
- SMA is positive in approximately 75% of AIH-1 patients and strongly favors AIH-1, particularly when combined with ANA at high titers 1, 3
- These antibodies frequently coexist in the same serum, which strengthens the diagnostic certainty 1
Type 2 AIH Markers (predominantly pediatric)
- Anti-LKM1 is positive in 70% of AIH-2 patients, with the target antigen clearly identified as cytochrome P450 2D6 (CYP2D6) 1
- Anti-LC1 is positive in 30-53% of AIH-2 patients, targeting formiminotransferase cyclodeaminase (FTCD) 1
- These antibodies often coexist, and titers correlate with disease activity 1
Critical pitfall: Anti-LKM1 and anti-LC1 can appear in 5-10% of chronic hepatitis C patients, so viral hepatitis must be excluded before diagnosing AIH-2 1
Secondary Testing When Primary Panel is Negative
If conventional autoantibodies are negative but AIH is still suspected clinically, test for anti-soluble liver antigen (anti-SLA/LP) and atypical perinuclear anti-neutrophil cytoplasmic antibodies (pANCA). 1
Disease-Specific Markers
- Anti-SLA/LP is the only AIH-specific autoantibody, present in 20-30% of both type 1 and type 2 AIH 1, 2
- Anti-SLA/LP requires ELISA or immunoblot for detection, as it cannot be detected by standard immunofluorescence 1, 4
- This antibody is associated with more severe disease and higher relapse rates after treatment withdrawal 1
Supplemental Markers
- pANCA is positive in 20-96% of AIH-1 patients and can be the only serological marker in suspected AIH-1 with negative ANA, SMA, and anti-SLA 1, 3
- Anti-F-actin (a subtype of SMA) provides additional diagnostic value when testing by immunofluorescence on kidney sections showing vessel/glomeruli patterns 1
Technical Methodology Requirements
Indirect immunofluorescence on rodent tissue sections (liver, kidney, stomach) remains the gold standard and superior method for autoantibody detection. 1, 5
Why Immunofluorescence is Essential
- Detects autoantibodies whose molecular targets are unknown 5
- ELISA for anti-actin misses diagnosis in approximately 20% of cases because actin is not the only target antigen of AIH-specific SMA reactivity 1
- HEp-2 cells alone are insufficient for screening AIH and should not be used as the primary substrate 1
Important caveat: While automated immunoassays are being developed, they currently lack sufficient validation and should only be used as complementary to immunofluorescence, not as replacements 1, 5
Diagnostic Algorithm
Initial evaluation: Order ANA, SMA, anti-LKM1, anti-LC1, and serum IgG levels 1, 4
If positive: Proceed with liver biopsy and exclude other etiologies (viral hepatitis, drug-induced liver injury, Wilson's disease, hereditary hemochromatosis) 1, 4, 2
If negative but clinical suspicion remains: Test anti-SLA/LP by ELISA/immunoblot and pANCA by immunofluorescence 1
If still negative: Consider repeat testing in a specialty laboratory with expanded panel including anti-F-actin, anti-LKM3, and other specific immunoassays 1
Supporting Laboratory Features
- Elevated serum IgG or γ-globulin levels (though normal in 10-39% of cases, particularly in acute presentations) 1, 2
- Aminotransferases typically elevated with ALP:AST ratio <1.5 2, 6
- Hypergammaglobulinemia with predominant elevation of β-globulin fraction 2
Note on seronegative AIH: Approximately 5% of patients with biopsy-proven AIH remain seronegative despite comprehensive testing; these cases require diagnostic scoring systems and may warrant a trial of corticosteroid therapy 1