Table 2

Baseline predictors of obstructive and restrictive lung disease

Obstructive lung diseaseRestrictive lung disease
N=303NormalNObstructive N=30OR (95% CI)NRestrictive N=41OR (95% CI)
Demographic characteristics
 Age, years30344 (13)3053 (9)1.06 (1.02 to 1.09)4151 (13)1.04 (1.01 to 1.07)
 Gender, female303230 (76%)3015 (50%)0.32 (0.15 to 0.68)4117 (41%)0.22 (0.11 to 0.44)
 Smoking status3033041
  Never112 (37%)2 (7%)113 (32%)1
  Past123 (41%)14 (47%)4.59 (0.99 to 21.33)16 (39%)0.64 (0.28 to 150)
  Current68 (22%)14 (47%)15.25 (3.14 to 73.99)12 (29%)1.45 (0.59 to 3.56)
Clinical characteristics
 Swollen joint count, 28 joints3034 (1–9)305 (2–11)1.01 (0.96 to 1.08)416 (3–14)1.05 (1.00 to 1.11)
 Tender joint count, 28 joints3035 (2–10)304 (1–15)1.04 (0.99 to 1.10)417 (3–13)1.07 (1.02 to 1.12)
 DAS28CRP(3)2513.70 (2.75–4.60)224.12 (3.53–4.88)1.41 (1.00 to 1.99)334.10 (3.35–5.68)1.44 (1.09 to 1.91)
 HAQ2970.625 (0.25–1.13)300.563 (0.38–1.0)1.01 (0.55 to 1.87)410.875 (0.38–1.63)2.28 (1.36 to 3.83)
 CRP, mg/l2513 (0–9)224 (8.5–13)1.00 (0.99 to 1.02)339 (2–17)1.00 (0.99 to 1.02)
 RF, positive27464 (23%)249 (38%)2.27 (0.90 to 5.75)3612 (33%)1.63 (0.74 to 3.58)
 ACPA, positive24654 (22%)173 (18%)0.70 (0.19 to 2.60)2410 (42%)2.25 (0.90 to 5.63)
 Shared epitope2832936
  0 allele116 (41%)9 (31%)115 (42%)1
  1 allele122 (43%)14 (48%)1.44 (0.58 to 3.57)15 (42%)086 (0.39 to 1.93)
  2 alleles45 (16%)6 (21%)1.79 (0.57 to 5.64)6 (17%)0.96 (0.33 to 2.80)
 RA, 1987 criteria303121 (40%)3012 (40%)0.94 (0.42 to 2.14)4124 (59%)2.56 (1.24 to 5.29)
 Nodules30313 (4%)303 (10%)2.60 (0.64 to 10.59)415 (12%)4.79 (1.46 to 15.71)
  • N=number of patients with available data. Values are mean (SD), median (IQR) for continuous variables or n (%) for categorical variables.

  • See Methods section for description of obstructive, restrictive and normal spirometry lung function test.

  • Bold type indicates statistical significance (p<0.05).

  • ACPA, anti-citrullinated protein antibody; CRP, C-reactive protein; DAS28, 28-joint Disease Activity Score; HAQ, Health Assessment Questionnaire; RA, rheumatoid arthritis; RF, rheumatoid factor; RLD, restrictive lung disease.