Autoimmune Hepatitis

Indications for Testing

Testing for AIH should be considered in all individuals who present with acute or chronic liver disease (including acute liver failure) or abnormal liver function tests (elevated aspartate aminotransferase [AST] and alanine aminotransferase [ALT]), particularly when hypergammaglobulinemia or features of other autoimmune disorders are present. ^, 

Testing is also indicated in patients with AIH to monitor the disease before, during, and after treatment. 

Criteria for Diagnosis

The heterogeneous presentation seen in AIH creates a diagnostic challenge. The simplified International Autoimmune Hepatitis Group (IAIHG) diagnostic criteria can be used in clinical settings to help address this challenge.  These criteria have a reported sensitivity of >80% and a reported specificity of >95% (with a cutoff of ≥7 points).  These criteria are not always necessary, and their clinical utility is limited to assisting in diagnosis of challenging cases. 

Laboratory Testing

Diagnosis

The diagnosis of AIH is based on a combination of biochemical testing, autoantibody testing, and histology in addition to the exclusion of other liver diseases. 

Biochemistry Tests

AIH is associated primarily with hypergammaglobulinemia, which is found in approximately 85% of patients with AIH and may be detected by either IgG testing or serum protein electrophoresis. ^,  Although IgG levels are usually elevated in AIH, IgA and IgM concentrations typically remain at normal levels.  Elevated IgA levels may suggest alcoholic steatohepatitis, whereas elevated IgM levels may suggest primary biliary cholangitis (PBC). 

Many patients with AIH present with persistently elevated bilirubin and aminotransferases (specifically AST and ALT). ^,  The concentrations in individuals with AIH range from just above the upper limit of normal to >50 times that amount.  Gamma-glutamyl transferase (GGT) may also be elevated in AIH.  An important consideration during the diagnostic process is that AST, ALT, and GGT may spontaneously return to normal levels while inflammatory activity persists, which can delay diagnosis, and thus treatment. 

Autoantibody Tests

AIH is associated with various autoantibodies; however, most of these autoantibodies are not specific to AIH, and their presence is not necessary for an AIH diagnosis. ^,  Autoantibody expression often varies over the course of the disease and may be detected later in patients who were initially seronegative. 

An initial autoantibody assessment tailored for AIH includes ANAs, SMAs, LKM type 1 (LKM1) autoantibodies, liver cytosol type 1 (anti-LC1) autoantibodies, and SLA/liver-pancreas (LP) autoantibodies.  Antimitochondrial antibodies (AMAs) may also be included to assist in differentiating AIH from PBC or to assess for the AIH-PBC variant form. ^,  According to the IAIHG, immunofluorescence (IFL) using rodent tissue is the preferred methodology for AIH antibody testing, with the exception of tests for anti-SLA/LP autoantibodies. ^,  However, this method is not standardized, and although commercial substrates exist, their quality varies.  Thus, other methods of testing, such as enzyme-linked immunosorbent assay (ELISA), are gaining popularity. 

ANAs and SMAs

ANAs are a marker of AIH-1 and are found in nearly half of patients with AIH-1. ^,  Although the homogeneous fluorescence pattern is most common in AIH, no particular staining pattern is consistently indicative of AIH, and the specific staining pattern does not appear to have clinical relevance.  Thus, HEp-2 staining is not needed when screening for AIH.  SMAs are also a marker of AIH-1 and are detected in about half of diagnosed patients.  Because SMA with reactivity against F-actin is more specific for AIH, testing for SMA/antiactin by ELISA is a useful diagnostic tool, although IFL is still preferred. ^,  In North America, the majority of patients with AIH have ANAs, SMAs, or both ; the two autoantibodies are frequently found together, which can improve the diagnostic strength. 

Anti-LKM1 and Anti-LC1

Anti-LKM1 and anti-LC1 autoantibodies are markers for AIH-2 that are often found in conjunction with one another.  The prevalence of anti-LKM1 and anti-LC1 autoantibodies in AIH-2 has been reported at 66% and 53%, respectively, although they are not specific to AIH, and both have been detected in patients with hepatitis C virus (HCV).  The specific target of each autoantibody has been determined; anti-LKM1 acts against cytochrome P450 2D6 (CYP2D6), and anti-LC1 acts against formininotransferase cyclodeaminase (FTCD). ^,  Because anti-LKM1 autoantibodies can be mistaken for AMAs when using IFL, ELISA testing should be used to confirm positivity. 

Anti-SLA/LP

Anti-SLA/LP autoantibodies are highly specific to AIH and thus have a high diagnostic value. ^,  These autoantibodies are detected in about 30% of patients with AIH but cannot be detected by IFL, so ELISA or Western blot testing must be used. ^, 

Other Autoantibody Tests

If initial autoantibody tests are negative, but clinical suspicion for AIH remains high, antineutrophil cytoplasmic antibody (ANCA) testing may be useful. ^,  Atypical perinuclear ANCAs (p-ANCAs), originally thought to be specific to PSC and inflammatory bowel disease (IBD), are now recognized as common in patients with AIH-1. ^, 

When anti-LKM1 autoantibodies are not detected, testing for anti-LKM3 autoantibodies (also associated with AIH-2) may be considered. ^, 

Prognosis

Autoantibodies

Of the autoantibodies assessed for diagnostic purposes, anti-LC1 (associated with AIH-2), anti-SLA/LP, and antiactin (a subset of SMAs) also have prognostic implications.  Anti-LC1 autoantibodies are associated with severe liver inflammation and a rapid progression to cirrhosis.  Anti-SLA/LP autoantibodies are associated with more severe histologic changes, as well as a higher likelihood of relapse, treatment dependence, and transplantation.  Antiactin autoantibodies are associated with higher likelihoods of treatment dependence, poorer treatment response, and liver failure. 

Antiasialoglycoprotein receptor autoantibodies (anti-ASGPR) can be detected in some patients with AIH and are associated with increased interface hepatitis and more frequent relapse in patients. (6-Sebode 2018) When these autoantibodies disappear during treatment, a sustained remission after treatment withdrawal is more likely. ^, , 

Other autoantibodies that may indicate more severe disease, treatment resistance, or long-term treatment dependence are antichromatin autoantibodies, anti-double-stranded DNA (anti-dsDNA) autoantibodies, and anticyclic citrullinated peptide (anti-CCP) autoantibodies. 

Other Tests

Biochemical assessment is more useful in diagnosis than in monitoring, but recent studies have indicated that elevated GGT levels may be useful as an independent predictor of treatment outcome. 

Histology reveals cirrhosis in 28-33% of patients at AIH diagnosis, and these patients, as well as those with bridging necrosis at diagnosis, have a poorer prognosis than those with neither. ^,  However, patients with cirrhosis do usually have treatment-responsive disease. 

Monitoring

In adults, autoantibody titers only roughly correlate with disease activity and are thus not useful in monitoring the disease.  However, in children, autoantibody titers (particularly in the case of anti-LC1) are biomarkers of disease activity and may be a useful tool in monitoring treatment response. 

For adults, the frequency of monitoring depends on the clinical situation of the patient.

Treatment-Related Testing

Because azathioprine therapy can cause severe myelosuppression in those with thiopurine methyltransferase (TPMT) deficiency, phenotyping or genotyping testing should be considered to assess the risk of such complications before initiating treatment.