Sensitivity, specificity and likelihood ratios for IA features
| IA feature | Sensitivity | Specificity | Positive LR | Negative LR | Post-test probability given positive test | Post-test probability given negative test |
| CRP | 54.1 | 72.7 | 2.0 | 0.6 | 25.9 | 10.0 |
| ESR | 66.7 | 54.5 | 1.5 | 0.6 | 20.6 | 9.7 |
| RF | 31.6 | 100.0 | Infinity | 0.7 | 100.0 | 10.8 |
| CCP | 44.7 | 100.0 | Infinity | 0.6 | 100.0 | 8.9 |
| Smoker | 31.6 | 80.0 | 1.6 | 0.9 | 21.8 | 13.1 |
| Erosive on X-ray† | 18.9 | 90.9 | 2.1 | 0.9 | 26.8 | 13.6 |
| Swollen joint in H/W | 86.8 | 45.5 | 1.6 | 0.3 | 21.9 | 4.9 |
| Any swollen joint | 86.8 | 45.5 | 1.6 | 0.3 | 21.9 | 4.9 |
| Tender joint H/W | 94.7 | 18.2 | 1.2 | 0.3 | 17.0 | 4.9 |
| Any tender joint | 97.4 | 9.4 | 1.1 | 0.3 | 15.9 | 4.7 |
| US GS ⩾1* | 92.1 | 18.2 | 1.1 | 0.4 | 16.6 | 7.1 |
| US GS ⩾2* | 76.3 | 63.6 | 2.1 | 0.4 | 27.0 | 6.2 |
| US GS 3* | 47.4 | 90.9 | 5.2 | 0.6 | 47.9 | 9.3 |
| US PD ⩾1* | 71.1 | 81.8 | 3.9 | 0.4 | 40.8 | 5.9 |
| US PD ⩾2* | 50.0 | 100.0 | Infinity | 0.5 | 100.0 | 8.1 |
| US FT in any finger | 47.4 | 63.6 | 1.3 | 0.8 | 18.7 | 12.7 |
| Erosive on US† | 52.6 | 72.7 | 1.9 | 0.7 | 25.4 | 10.3 |
Features in bold are included in the diagnostic algorithm shown in fig 1.
*A semi-quantitative score as stated in any joint (ie, minimum of one joint).
†At least one erosion in any joint.
CCP, cyclic citrullinated peptide; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; FT, flexor tenosynovitis; GS, grey scale; H/W, hand or wrist joints; IA, inflammatory arthritis; LR, likelihood ratio; PD, power Doppler; RF, rheumatoid factor; US, ultrasound.