Proposed DO-GAP index and staging system
| Predictor | Category | Points | |
| Distance | 6MWT distance | ||
| ≥250 metres | 0 | ||
| <250 metres | 5 | ||
| Oxygen | No hypoxia | 0 | |
| Exertional hypoxia | 5 | ||
| Gender | Female | 0 | |
| Male | 1 | ||
| Age (years) | ≤60 | 0 | |
| 61–65 | 1 | ||
| >65 | 2 | ||
| Physiology | FVC, % predicted | ||
| >75 | 0 | ||
| 50–75 | 1 | ||
| <50 | 2 | ||
| DLCO, % predicted | |||
| >55 | 0 | ||
| 36–55 | 1 | ||
| ≤35 | 2 | ||
| Cannot perform | 3 | ||
| Total possible points | 18 | ||
| Points | 0–4 | 5–10 | 11–18 |
| Stage | I | II | III |
DLCO, diffusion capacity for carbon monoxide; DO-GAP, distance-oxygen-gender-age-physiology; FVC, forced vital capacity; 6MWT, 6 min walk test distance.