Rheumatoid Factor (RF): Significance, Testing & Diagnostic Role

Rheumatoid factor (RF) is an autoantibody (usually IgM) targeting the Fc portion of IgG. It forms immune complexes that deposit in joints, driving inflammation in rheumatoid arthritis (RA).

Key Points

• Not specific to RA: Present in 70–80% of RA, but also in Sjögren's, lupus, chronic infections, and 5–10% of healthy elderly.
• Diagnostic role: Supports RA diagnosis when combined with clinical criteria (symmetrical polyarthritis, morning stiffness, erosions, anti-CCP).
• Prognostic value: High titers correlate with more erosive disease.
• Monitoring: Serial RF less useful than disease activity scores (DAS28) and acute-phase reactants.

Anti-CCP is more specific for RA. RF alone does not confirm or exclude RA.