Criteria for refined risk stratification in the three-stratum model and the four-stratum model based on World Health Organization functional class (WHO FC), 6-min walk distance (6MWD) and brain natriuretic peptide (BNP)/N-terminal pro-BNP (NT-proBNP)
| Points assigned | ||||
| 1 | 2 | 3 | 4 | |
| Three-stratum model | ||||
| WHO FC | I or II | III | IV | |
| 6MWD, m | >440 | 440–165 | <165 | |
| BNP,# ng·L−1 | <50 | 50–800 | >800 | |
| NT-proBNP,# ng·L−1 | <300 | 300–1100 | >1100 | |
| Four-stratum model | ||||
| WHO FC | I or II | III | IV | |
| 6MWD, m | >440 | 440–320 | 319–165 | <165 |
| BNP,# ng·L−1 | <50 | 50–199 | 200–800 | >800 |
| NT-proBNP,# ng·L−1 | <300 | 300–649 | 650–1100 | >1100 |
#: the cut-off values for 6MWD and BNP were obtained from Registry to Evaluate Early and Long-term PAH Disease Management (REVEAL) Lite 2 [9], while the cut-off values for NT-proBNP were derived from receiver operating curve analysis of all patients from the present analysis with baseline NT-proBNP values between 300 and 1100 ng·L−1. When both BNP and NT-proBNP were available, NT-proBNP was used.