Which autoantibody is considered highly sensitive but may lack specificity due to false positives?

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

Answer: (B)

The main idea is sensitivity versus specificity in autoantibody testing. Antinuclear antibodies (ANA) are the most sensitive screening tests for autoimmune diseases, especially systemic lupus erythematosus, but they are not disease-specific. A positive ANA can occur in many people without a defined autoimmune disease—healthy individuals, the elderly, infections, or with certain medications—leading to false positives. Because of this, ANA is used to flag possible autoimmune activity and prompt more specific testing, rather than to diagnose a particular disease on its own. In contrast, antibodies like anti-dsDNA or anti-CCP are more specific for specific diseases (SLE and RA, respectively), but may not be as sensitive. RF is also sensitive but less specific. Therefore, ANA best fits being highly sensitive with potential false positives.