Which of the following antibodies is most specific for rheumatoid arthritis and is associated with more severe, erosive disease?

Question

Accepted Answer

A. Anti-cyclic citrullinated peptide (anti-CCP) antibody. ## Anti-CCP Antibody in Rheumatoid Arthritis

**Key Point:** Anti-CCP antibodies are the most specific serological marker for RA, with specificity >95%, and are present in 60–70% of RA patients, including those who are rheumatoid factor (RF) negative.

**High-Yield:** Anti-CCP positivity is associated with:
- More severe, erosive joint disease
- Worse functional outcomes
- Greater radiographic progression
- Presence even in early/seronegative RA

### Comparison of RA Serological Markers

| Marker | Specificity | Sensitivity | Clinical Significance |
| --- | --- | --- | --- |
| Anti-CCP | >95% | 60–70% | Most specific; predicts erosive disease |
| Rheumatoid Factor (RF) | 80–85% | 70–80% | Less specific; can be positive in other autoimmune diseases |
| ANA | 40–60% in RA | Variable | Non-specific; more associated with SLE |
| ASMA | <5% in RA | N/A | Associated with autoimmune hepatitis, not RA |

**Clinical Pearl:** A patient who is RF-negative but anti-CCP positive has "seronegative RA" by traditional RF criteria but is still at high risk for erosive disease and should be treated aggressively.

**Mnemonic:** **CCP = Citrullinated peptide = Cartilage-damaging Predictor** — anti-CCP predicts more severe, erosive disease.

Answer

B. Rheumatoid factor (IgM against Fc of IgG)

Answer

C. Antinuclear antibody (ANA)

Answer

D. Anti-smooth muscle antibody (ASMA)

Which of the following antibodies is most specific for rheumatoid arthritis and is associated with more severe, erosive disease?

Explanation

Anti-CCP Antibody in Rheumatoid Arthritis

Comparison of RA Serological Markers

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Marker	Specificity	Sensitivity	Clinical Significance
Anti-CCP	>95%	60–70%	Most specific; predicts erosive disease
Rheumatoid Factor (RF)	80–85%	70–80%	Less specific; can be positive in other autoimmune diseases
ANA	40–60% in RA	Variable	Non-specific; more associated with SLE
ASMA	<5% in RA	N/A	Associated with autoimmune hepatitis, not RA