Table 4. Multivariable mixed-effects Cox proportional hazards regression models in non-CPFE patients and the two CPFE subgroups in the derivation IPF cohort.
| Subgroup | Baseline severity and PFTs changes models | C-index | p-value | Hazard ratio | 95% CI | |
|---|---|---|---|---|---|---|
| Lower | Upper | |||||
| Non-CPFE IPF patients (n=130, 61 deaths) |
1-year FVC relative decline | 0.821 | 3.02×10-8 | 1.082 | 1.052 | 1.113 |
| Binary 1-year FVC decline (5%) | 0.805 | 1.09×10-5 | 3.824 | 2.104 | 6.953 | |
| Binary 1-year FVC decline (10%) | 0.811 | 4.96×10-7 | 4.261 | 2.422 | 7.497 | |
| 1-year DLco relative decline | 0.803 | 0.0001 | 1.038 | 1.018 | 1.058 | |
| Binary 1-year DLco decline (10%) | 0.800 | 0.0010 | 2.764 | 1.511 | 5.055 | |
| Binary 1-year DLco decline (15%) | 0.811 | 4.69×10-7 | 4.211 | 2.407 | 7.366 | |
| CPFE
patients with emphysema < 10% (n=119, 63 deaths) |
1-year FVC relative decline | 0.716 | 6.46×10-5 | 1.051 | 1.026 | 1.077 |
| Binary 1-year FVC decline (5%) | 0.721 | 0.0001 | 3.000 | 1.705 | 5.279 | |
| Binary 1-year FVC decline (10%) | 0.685 | 0.025 | 1.983 | 1.091 | 3.604 | |
| 1 -year DLco relative decline | 0.727 | 0.0003 | 1.035 | 1.016 | 1.055 | |
| Binary 1-year DLco decline (10%) | 0.682 | 0.173 | 1.453 | 0.849 | 2.486 | |
| Binary 1-year DLco decline (15%) | 0.696 | 0.017 | 1.979 | 1.131 | 3.464 | |
| CPFE
patients with emphysema ≥1% (n=103, 73 deaths) |
1-year FVC relative decline | 0.714 | 0.008 | 1.034 | 1.009 | 1.061 |
| Binary 1-year FVC decline (5%) | 0.714 | 0.016 | 1.868 | 1.126 | 3.100 | |
| Binary 1-year FVC decline (10%) | 0.715 | 0.002 | 2.540 | 1.421 | 4.539 | |
| 1-year DLco relative decline | 0.732 | 1.24×10-5 | 1.033 | 1.018 | 1.049 | |
| Binary 1-year DLco decline (1%) | 0.703 | 0.058 | 1.619 | 0.983 | 2.665 | |
| Binary 1-year DLco decline (15%) | 0.732 | 7.61×10-5 | 2.674 | 1.643 | 4.353 | |
Multivariable mixed-effects Cox regression models were used to investigate associations with mortality for 1-year FVC decline and 1-year DLco decline after adjusting for patient age, sex, smoking status (never versus ever), antifibrotic use (never versus ever) and baseline disease severity estimated using DLco. Binary 1-year FVC decline uses 5% and 10% relative decline as thresholds, and binary 1-year DLco decline uses 10% and 15% relative decline as thresholds. Separate centres/countries within the derivation cohort were modelled as multilevel with random effects between centres/countries (a random intercept per centre/country). All models passed Schoenfeld residuals test. CPFE: combined pulmonary fibrosis and emphysema; IPF: idiopathic pulmonary fibrosis; PFT: pulmonary function test; FVC: forced vital capacity; DLco: diffusing capacity of the lung for carbon monoxide; C-index: concordance index; CI: confidence interval.