| All patients | Patients who did not fulfil the imaging arm† | |||
| OR (95% CI) | p Value | OR (95% CI) | p Value | |
| Male gender | 2.1 (1.1 to 4.1) | 0.026 | 2.2 (1.2 to 3.9) | 0.007 |
| IBP (according to experts; 4 of 5)* | 3.0 (1.6 to 5.9) | 0.001 | 2.2 (1.2 to 3.8) | 0.006 |
| Good response to NSAID | 2.7 (1.4 to 5.1) | 0.02 | 2.8 (1.6 to 4.9) | <0.001 |
| Enthesitis of the heel, current or past (%) | 0.7 (0.3 to 1.8) | ns | 1.0 (0.5 to 2.1) | ns |
| Peripheral arthritis, current or past (%) | 3.7 (1.7 to 8.0) | 0.001 | 2.7 (1.5 to 5.0) | 0.002 |
| Uveitis, current or past | 1.7 (0.6 to 4.7) | ns | 1.4 (0.6 to 3.5) | ns |
| Dactylitis, current or past | 5.3 (0.9 to 29.4) | ns | 7.2 (1.5 to 33.3) | 0.012 |
| Psoriasis, current or past | 2.5 (0.7 to 8.8) | ns | 2.5 (0.9 to 7.2) | ns |
| IBD, current or past | 6.5 (0.6 to 66.7) | ns | 3.9 (0.5 to 33.3) | ns |
| Family history of SpA (AS, reactive arthritis, uveitis, psoriasis, IBD) | 1.3 (0.6 to 2.8) | ns | 1.5 (0.8 to 2.7) | ns |
| Anterior lumbar flexion (Schober’s test; cm) | 0.9 (0.8 to 1.0) | 0.046 | 0.8 (0.7 to 0.9) | 0.003 |
| Lateral lumbar flexion (cm) | 0.9 (0.9 to 1.0) | 0.004 | 0.9 (0.9 to 1.0) | 0.021 |
| Chest expansion, cm | 1.1 (0.9 to 1.3) | ns | 1.1 (0.9 to 1.3) | ns |
| HLA-B27 | 2.8 (1.5 to 5.4) | 0.002 | 2.7 (1.6 to 4.8) | <0.001 |
| Elevated CRP, above upper normal limit | 1.6 (0.7 to 3.3) | ns | 1.9 (1.0 to 3.6) | ns |
| Definite radiographic sacroiliitis (⩾ grade 2 bilateral or ⩾ grade 3 unilateral) | 32.3 (6.6 to 166.7) | <0.001 | NA | – |
| Unilateral grade 2 radiographic sacroiliitis | 7.8 (1.3 to 50) | 0.028 | 8.2 (2.0 to 33.3) | 0.003 |
| Active inflammation of sacroiliac joints, MRI (n = 495) | 66.7 (22.7 to 200) | <0.001 | NA | – |
The variables definite radiographic sacroiliitis and active inflammation of sacroiliac joints on magnetic resonance imaging (MRI) were not entered into the logistic regression analysis of patients who did not fulfil the imaging arm. *Inflammatory back pain (IBP) according to experts; at least four of five parameters present.14 †n = 374 patients who did not fulfil the imaging arm were analysed. The imaging arm of the criteria refers to the presence of definite radiographic sacroiliitis (grade 2 bilaterally or grade 3–4 unilaterally) or active sacroiliitis on MRI in conjunction with at least one clinical parameter. AS, ankylosing spondylitis; CRP, C-reactive protein; IBD, inflammatory bowel disease; NA, not assessed; ns, non-significant; NSAID, non-steroidal anti-inflammatory drug; SpA, spondyloarthritis.