| Variable | Hazard ratio (95% CI) | p-value |
| Age yrs | 1.02 (0.98–1.07) | ns |
| Smoking pack-yrs | 0.99 (0.97–1.02) | ns |
| Time to diagnosis months | 1.01 (0.99–1.03) | ns |
| BMI m·kg−2 | 0.89 (0.80–0.98) | 0.0155 |
| MRC dyspnoea score | 2.52 (1.76–3.62) | <0.0001 |
| 6MWD m | 1.00 (1.00–1.00) | ns |
| 6MWD % pred | 0.98 (0.96–0.99) | 0.0007 |
| Desaturation at 6MWT# | 0.54 (0.32–0.84) | 0.0052 |
| PA-a,O2 mmHg | 1.03 (1.01–1.05) | 0.0063 |
| FVC % pred | 0.97 (0.95–0.99) | 0.0039 |
| DL,CO % pred | 0.94 (0.92–0.97) | <0.0001 |
| CPI | 1.06 (1.03–1.10) | <0.0001 |
| HRCT fibrosis score % of total lung volume | 1.03 (1.00–1.07) | 0.0497 |
| BAL total cell count cells·mL−1 | 1.00 (1.00–1.00) | 0.0009 |
| Concomitant emphysema | 1.82 (0.90–3.66) | 0.096 |
BMI: body mass index; MRC: Medical Research Council; 6MWD: 6-min walking distance; % pred: % predicted; 6MWT: 6-min walking test; PA–a,O2: alveolar–arterial oxygen tension difference; FVC: forced vital capacity; DL,CO: diffusing capacity of the lung for carbon monoxide; CPI: composite physiologic index; HRCT: high-resolution computed tomography; BAL: bronchoalveolar lavage; ns: not significant. #: no desaturation (arterial oxygen saturation ≤88%) during the 6MWT.