Introduction: The interstitial lung disease-gender age physiology (ILD-GAP) model has been proposed on the lines of GAP-idiopathic pulmonary fibrosis (IPF) to predict mortality in chronic ILDs, other than IPF. We replaced diffusion capacity of lung for carbon monoxide (DLCO) with the easy to perform 6-minute walk distance (6 MWD) in the ILD-GAP and proposed the new modified classification (TNMC)-ILD-GAP model. Our aim was to demonstrate the usefulness of the TNMC-ILD-GAP as a predictor of mortality in all chronic ILDs and compare the results with the ILD-GAP.
Methods: It was a retrospective observational study conducted at a tertiary care centre. Baseline characteristics of the patients among different ILD groups were analysed. A 3-year follow-up was recorded. The results were compared with the original ILDGAP model. Chi-square and paired t-test was used for comparison of qualitative and quantitative data, respectively.
Results: Mean ages were 62.34 (±9.85), 57.9 (±11.6), 46.1 (±14.6) and 55.5 (±14.7) in IPF, non-specific interstitial pneumonitis (NSIP), connective tissue disease (CTD) and unclassifiable groups, respectively. There were 50%, 18%, 26% and 55% males in the four categories respectively. Mean 6 MWD was 227 m, 302 m, 342 m, and 332 m. Mean PaO2 was 64 mmHg, 70 mmHg, 75 mmHg, 69 mmHg. Mean forced vital capacity (FVC) (percentage predicted) was 52, 49, 51 and 54. Most of the patients had comorbidities, among which pulmonary hypertension was the most common. Mortality with ILD-GAP model and TNMC-ILD-GAP showed concordant results as the difference in mortality predicted by ILD-GAP and the TNMC-ILD-GAP models was statistically insignificant (P > 0.050).
Conclusion: 6 MWD can serve as a reliable replacement for DLCO in the ILD-GAP model, especially in resource limited settings.
