A 40-year-old woman with SLE develops seizures and psychosis. Anti-ribosomal P antibodies are positive. Anti-dsDNA is elevated, and complement C3 is low. Which autoantibody is most specific for SLE diagnosis?
- A Anti-dsDNA antibody
- B Anti-Sm (Smith) antibody ✓
- C ANA (antinuclear antibody)
- D Anti-histone antibody
Correct answer: B. Anti-Sm (Smith) antibody
Explanation
Anti-Sm (Smith) antibody is highly specific (approximately 99%) for SLE, though it is present in only 20-30% of patients. Anti-dsDNA is also specific and correlates with disease activity (especially lupus nephritis) but can occasionally occur in other conditions. ANA is sensitive (95%) but not specific. Anti-histone is associated with drug-induced lupus.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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