Baseline demographic, clinical and radiographic characteristics of all patients stratified by baseline smoking status and by baseline occupational activity
| Assessment | N=184 mean (SD) or n (%) | Blue-collar jobs* N=65 mean (SD) or n (%) | White-collar jobs* N=71 mean (SD) or n (%) | Smokers† N=49 mean (SD) or n (%) | Non-smokers† N=78 mean (SD) or n (%) |
|---|---|---|---|---|---|
| Age (years) | 43 (12) | 40 (12) | 41 (11) | 38 (11) | 42 (12) |
| Male gender (%) | 129 (70) | 56 (86) | 45 (63) | 40 (82) | 49 (63) |
| HLA-B27 positive (%) | 149 (83) | 50 (79) | 61 (88) | 43 (88) | 61 (78) |
| Symptoms duration (years) | 20 (12) | 17 (10) | 18 (9) | 16 (10) | 20 (11) |
| Disease duration (years) | 11 (9) | 9 (8) | 11 (8) | 8 (6) | 11 (9) |
| ASDAS-CRP | 2.6 (1.0) | 2.9 (1.0) | 2.4 (0.9) | 2.8 (1.0) | 2.6 (1.1) |
| BASDAI (0–10) | 3.4 (2.0) | 3.7 (2.0) | 2.9 (1.9) | 3.4 (1.9) | 3.2 (2.2) |
| CRP (mg/L) | 17.4 (23.3) | 18.2 (21.6) | 15.7 (23.0) | 18.9 (23.0) | 17.9 (25.9) |
| Elevated CRP (%)‡ | 85 (48) | 30 (48) | 34 (50) | 25 (53) | 37 (49) |
| mSASSS (0–72) | 10.8 (15.2) | 11.0 (14.7) | 6.4 (8.6) | 9.9 (15.9) | 9.3 (13.7) |
| mSASSS >0 (%) | 140 (81) | 50 (81) | 50 (78) | 31 (72) | 60 (80) |
| NSAIDs (%) | 125 (68) | 46 (71) | 50 (70) | 36 (73) | 54 (69) |
| University education (%) | 14 (8) | 1 (2) | 12 (17) | 1 (2) | 9 (12) |
| Monthly personal income ≥€1588 (%) | 56 (35) | 17 (28) | 32 (52) | 16 (38) | 23 (34) |
| Monthly family income ≥€3176 (%) | 21 (19) | 4 (9) | 14 (35) | 6 (21) | 10 (21) |
| Smoker (%) | 49 (39) | 23 (51) | 17 (33) | – | – |
| Blue-collar worker (%) | 65 (48) | – | – | 23 (58) | 22 (39) |
*Baseline occupational activity was missing for 48 patients (6 retired, 25 work-disabled, 4 housewives, 2 not working for own choice, 3 students, 1 unemployed and 7 with missing baseline occupational activity missing).
†Baseline smoking status was missing for 57 patients.
‡The cut-off was 10 mg/L for the Dutch patients and 5 mg/L for the Belgian and French patients.
ASDAS-CRP, Ankylosing Spondylitis Disease Activity Score (C reactive protein); BASDAI, Bath Ankylosing Spondylitis Disease Activity Score; CRP, C reactive protein; HLA-B27, human leucocyte antigen; mSASSS, modified Stoke Ankylosing Spondylitis Spine Score; NSAIDs, non-steroidal anti-inflammatory drugs.