| Classification system | Interpretation |
| A0 | No evidence of acute rejection |
| A1 | Minimal acute cellular rejection |
| A2 | Mild acute cellular rejection (treatment required) |
| A3 | Moderate acute cellular rejection |
| A4 | Severe acute cellular rejection |
| B0 | No airway inflammation |
| B1R | Mild airway inflammation |
| B2R | Moderate–severe airway inflammation |
| C0 | No evidence of obliterative bronchiolitis |
| C1 | Presence of obliterative bronchiolitis |