Anti-CCP — Rheumatoid Arthritis
Test Characteristics
| Metric | Value |
|---|---|
| False-negative rate | 33% (sensitivity 67%) |
| False-positive rate | 5% (specificity 95%) |
| Bayes factor (positive test) | 10× |
| Bayes factor (negative test) | 1/3× |
| Base rate | 0.5% of US adults |
Interpreting Results
| Scenario | Prior | + Result | − Result |
|---|---|---|---|
| Unselected adult | 0.5% | 10 × 0.5% = 5%0.5%× 105% | 1/3 × 0.5% = 0.17%0.5%÷ 30.17% |
| Symmetric polyarthritis, morning stiffness >1 hr | 15% | 10 × 15% ≥ 100%15%× 10100% | 1/3 × 15% = 5%15%÷ 35% |
10 × 15% ≥ 100%15%× 10100%: exact posterior is 64%. Better than RF. Negative (1/3×) is weak — misses a third of RA cases. May be positive years before clinical onset.
- + result: risk goes from identical twin (0.5%) to vegetarian (5%)
- − result: barely changes it
Sources:
- Meta-analysis, Ann Intern Med, 2007. PubMed 17548411.
- PMC. Anti-CCP: a truly helpful RA test?.