Antibodies against actin are a diagnostic test for type 1 autoimmune hepatitis.
Type 1 autoimmune hepatitis is a rare disease (10-20 cases per 1 million population) affecting mainly women (80%), mostly between the ages of 10 and 20 or between 45 and 70 years. There is usually a history of immune disorder with thyroiditis, diabetes, connective tissue disease, etc. Occasionally it presents with severe hepatitis and jaundice, although it is usually mild with a slow progression to cirrhosis. Laboratory findings include increased transaminases (x5), cholestasis (not always), increased polyclonal IgG immunoglobulins, antibodies against smooth muscle fibers (ASMA), and specific anti-actin antibodies. Antinuclear antibodies with a homogeneous pattern of fluorescence without the presence of anti-DNA antibodies are found in 40% of cases and lead to the emergence of this disease called lupoid hepatitis. Antibodies against SLA (soluble liver antigen) are positive in 5 to 10% of cases and are highly specific. Treatment of autoimmune hepatitis type 1 is long-term and includes corticosteroids and azathioprine.
The presence of antibodies against actin has an 85% sensitivity and specificity for autoimmune hepatitis. About 0.7% of cases of hepatitis C, some drugs, and some autoimmune diseases can give false-positive results.