Which antibody is most characteristic of primary biliary cirrhosis?

• A. Anti-SMA antibodies
• B. Anti-HBs antibodies
• C. Anti-Nuclear antibodies
• D. Anti-Mitochondrial antibodies

Answer: (D)

Anti-mitochondrial antibodies are the best answer because they are the serologic hallmark of primary biliary cirrhosis. In PBC, autoimmune destruction of small intrahepatic bile ducts leads to cholestasis, and most patients have high-titer AMA, particularly against the E2 subunit of the pyruvate dehydrogenase complex located on the mitochondrial membrane. This specificity makes AMA the most characteristic and diagnostic antibody for this disease. Other antibodies can appear in autoimmune conditions or infections but do not define PBC: smooth muscle antibodies are more typical of autoimmune hepatitis, hepatitis B surface antibodies reflect prior infection or immunity, and antinuclear antibodies are nonspecific and less diagnostic for PBC. Keep in mind that a minority of patients may be AMA-negative, and diagnosis can still be made with clinical, biochemical (cholestatic LFTs), and histologic findings.