Classification of bronchiolitis obliterans syndrome (BOS)53
| BOS 0-p, potential BOS stage; FEF25–75, mid expiratory flow rate; FEV1, forced expiratory volume in 1 s. | |
| The mean of the two highest (not necessarily consecutive) measurements represents the baseline value with which the subsequent measurements are compared. | |
| BOS 0 | FEV1 >90% of baseline and FEF25–75 >75% of baseline |
| BOS 0-p | FEV1 81–90% of baseline and/or FEF25–75 ⩽75% of baseline |
| BOS 1 | FEV1 66–80% of baseline |
| BOS 2 | FEV1 51–65% of baseline |
| BOS 3 | FEV1 ⩽50% of baseline |