AIH diagnosis is based on histological, serological, clinical and immunological features that distinguish the disease from other hepatobiliary diseases such as primary biliary cirrhosis and chronic hepatitis C. Autoantibody detection has allowed the disease to be characterised into 3 different groups; AIH type 1, 2 and 3.
Type 1 is the most common form characterised by the presence of anti-smooth muscle antibodies. The target autoantigen that is the most specific, is F-actin.
AIH-type 2 is less common and usually displays an acute onset of hepatitis. Liver/kidney microsomal antibodies (LKM-1), which are directed against cytochrome P450, is utilised as a common diagnostic marker for the identification of this disease. LKM-1 has been studied extensively as a differential diagnostic marker in order to discount other hepatic diseases.
Liver cytosol 1 (LC-1) antibodies have been found to be present in up to 50% of patients with AIH-type 2. LC-1 seems to correlate more closely with disease activity and can be useful as an identifier of residual inflammation.
AIH-type 3 has a lower prevalence than type 2 and generally manifests in 20-40 year old patients. It can be characterised by the presence of soluble liver pancreas antigen (SLA/LP). A high percentage of patients with SLA/LP autoantibodies also have other autoimmune serological markers. It can be difficult to clinically distinguish AIH-type 1 from AIH-type 3 and whether AIH-type 3 is a distinct subtype of AIH remains controversial.
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