A 52-year-old female presents with persistent pain, stiffness, and symmetric swelling of the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of both hands, lasting > 1 hour every morning. Radiographs reveal marginal bony erosions and joint space narrowing. Which serological marker is most specific (> 95%) for confirming rheumatoid arthritis?

Answer and explanation

Correct answer: C. Anti-Cyclic Citrullinated Peptide (Anti-CCP / ACPA) Antibodies

  1. Step 1: While Rheumatoid Factor (RF) has moderate sensitivity (60-70%), it can be positive in diverse autoimmune, chronic infectious, and pulmonary disorders.
  2. Step 2: Anti-Cyclic Citrullinated Peptide (anti-CCP / ACPA) antibodies have superior specificity (> 95-98%) for rheumatoid arthritis and predict aggressive, erosive disease.
Answer
Anti-Cyclic Citrullinated Peptide (Anti-CCP / ACPA) Antibodies.
Why not the others: 'Antinuclear Antibodies' are non-specific for RA and screen for systemic lupus erythematosus; 'ESR' is a general non-specific inflammatory acute-phase reactant; 'Rheumatoid Factor' has lower specificity and is positive in hepatitis C, Sjogren's, and normal elderly.

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