Classification of asthma severity by clinical features before treatment
| Intermittent |
| Symptoms less than once a week |
| Brief exacerbations |
| Nocturnal symptoms not more than twice a month |
| FEV1 or PEF ≥80% pred |
| PEF or FEV1 variability <20% |
| Mild persistent |
| Symptoms more than once a week but less than once a day |
| Exacerbations may affect activity and sleep |
| Nocturnal symptoms more than twice a month |
| FEV1 or PEF ≥80% pred |
| PEF or FEV1 variability <20–30% |
| Moderate persistent |
| Symptoms daily |
| Exacerbations may affect activity and sleep |
| Nocturnal symptoms more than once a week |
| Daily use of inhaled short-acting β2-agonist |
| FEV1 or PEF 60–80% pred |
| PEF or FEV1 variability >30% |
| Severe persistent |
| Symptoms daily |
| Frequent exacerbations |
| Frequent nocturnal asthma symptoms |
| Limitation of physical activities |
| FEV1 or PEF ≤60% pred |
| PEF or FEV1 variability >30% |
FEV1: forced expiratory volume in one second; PEF: peak expiratory flow; % pred: % predicted.