Which autoantibody is best for the diagnosis of rheumatoid arthritis?

• A. RF
• B. ANA
• C. Anti-CCP
• D. Anti-dsDNA

Answer: (C)

Anti-CCP antibodies are the most useful single autoantibody for diagnosing rheumatoid arthritis because they are highly specific for RA. They target citrullinated proteins that accumulate in RA joints, and a positive test strongly supports RA with a high specificity (around 95%), meaning few false positives. Rheumatoid factor, while sensitive, is less specific and can be positive in other diseases and in some healthy people, limiting its diagnostic value on its own. ANA is a general autoimmune marker and lacks specificity for RA, and anti-dsDNA is characteristic of systemic lupus erythematosus rather than RA. Therefore, anti-CCP provides the best balance of accuracy for confirming RA, especially when combined with the clinical picture and other criteria, though some patients may still be seronegative for anti-CCP.