Baseline characteristics: activity and metrology
| Characteristic | SpA | nr-axSpA | AS | M-W/FET p value |
| ASDAS-CRP, median (IQR) | 2.2 (1.4–2.8) | 2.0 (1.1–2.3) | 2.4 (1.7–2.8) | 0.022 |
| BASDAI, median (IQR) | 2.6 (1.2–4.7) | 2.7 (1.0–4.9) | 2.4 (1.2–3.7) | 0.362 |
| CRP (mg/L) | 4.3 (1.2–12.0) | 2.5 (0.8–8.2) | 7.1 (2.6–14.9) | <0.001 |
| ESR (mm/h) | 8.0 (4.0–17.8) | 7.0 (3.0–16.0) | 12.0 (4.4–22.0) | 0.007 |
| BASFI, median (IQR) | 1.4 (0.5–2.1) | 1.1 (0.3–2.9) | 1.8 (0.7–3.3) | 0.030 |
| Metrology | ||||
| Modified Schober (cm), median (IQR) | 4.0 (3.0–5.0) | 4.5 (3.5–5.5) | 4.0 (3.0–5.0) | <0.001 |
| Occiput to wall (cm), median (IQR) | 0.0 (0.0–0.0) | 0.0 (0.0–0.0) | 0.0 (0.0–0.0) | <0.001 |
| Chin–chest distance (cm), median (IQR) | 1.5 (0.0–3.0) | 1.0 (0.0–2.0) | 2.0 (0.0–3.0) | 0.008 |
| Chest expansion (cm), median (IQR) | 4.0 (3.0–6.0) | 4.0 (3.0–6.0) | 3.8 (2.0–6.0) | 0.136 |
AS, ankylosing spondylitis; ASDAS-CRP, Ankylosing Spondylitis Disease Activity Score based on CRP; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; M-W/FETp, Mann-Whitney/Fisher exact test p value; nr-axSpA, non-radiographic axial spondyloarthritis; SpA, spondyloarthritis.