Which autoantibody is most specific for systemic lupus erythematosus and often used to confirm the diagnosis?

• A. Anti-Sm antibodies
• B. Anti-double-strand DNA antibodies
• C. Anti-Ro antibodies
• D. Anti-La antibodies

Answer: (D)

Autoantibody testing in SLE uses specificity to confirm the diagnosis. The anti-Smith antibodies are the most specific for systemic lupus erythematosus; when they are present, they strongly support the diagnosis because they are rarely seen in other diseases. Anti-dsDNA antibodies are also highly associated with SLE and are useful for monitoring disease activity, especially lupus nephritis, but they are not as universally specific as anti-Smith. Antibodies to Ro/SSA and La/SSB are more common in Sjogren’s syndrome and can occur in SLE but are not specific for lupus, so they are not used to confirm the diagnosis.