American Board of Internal Medicine (ABIM) Certification Practice Exam

Which antibody test is vital for diagnosing primary biliary cholangitis (formerly primary biliary cirrhosis)?

1. Anti-SMA antibody

2. Antimitochondrial antibody

3. Anti-LKM antibody

4. ANA

The correct answer is: Antimitochondrial antibody

The diagnosis of primary biliary cholangitis (PBC) is primarily established through the detection of antimitochondrial antibodies (AMA) in the serum. These antibodies are highly specific for PBC and are found in approximately 90% of patients diagnosed with the condition. The presence of these antibodies is a key marker that helps differentiate PBC from other liver diseases and autoimmune conditions. Antimitochondrial antibodies target components of the inner mitochondrial membrane, and their detection is critical in confirming the diagnosis of PBC, often in conjunction with clinical symptoms and liver function tests that suggest cholestasis. In contrast, the other antibody tests listed are associated with different conditions. Anti-smooth muscle antibodies (anti-SMA) are usually seen in autoimmune hepatitis, while anti-LKM (liver-kidney microsome) antibodies are typically present in certain types of autoimmune hepatitis. Antinuclear antibodies (ANA) are more commonly associated with systemic lupus erythematosus and other connective tissue diseases but are not specific for PBC. Therefore, the identification of antimitochondrial antibodies is essential in the clinical workup of patients suspected of having primary biliary cholangitis.