Baseline characteristics of asymptomatic subjects classified according to level of airway responsiveness (PC20) at start of study
| PC20 ⩽8 mg/ml(n = 38) | PC20 >8 mg/ml(n = 390) | |
|---|---|---|
| Results are presented as number (%) unless otherwise stated. | ||
| PC20, concentration of methacholine provoking a 20% fall in FEV1; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity. | ||
| *Skin reaction to two or more common aeroallergens. | ||
| †Urticaria, eczema or hay fever. | ||
| Mean (SD) age (years) | 20.2 (4.1) | 21.9 (7.2) |
| Smoking | 4 (10.5) | 34 (8.7) |
| Atopy* | 18 (47.4) | 129 (33.1) |
| Atopic diathesis† | 12 (31.6) | 68 (17.4) |
| Self-reported rhinitis | ||
| Non-specific | 20 (52.6) | 152 (39.0) |
| To animals | 13 (34.2) | 83 (21.3) |
| To pollen | 13 (34.2) | 70 (17.9) |
| Ownership of pet at any time | 35 (92.1) | 358 (91.8) |
| Family history of asthma | 10 (26.3) | 69 (17.7) |
| Spirometry | ||
| Mean (SD) FEV1 (% predicted) | 97.3 (8.3) | 104.8 (11.7) |
| FEV1 ⩽80% predicted | 0 | 8 (2.0) |
| Mean (SD) FEV1/FVC | 86.5 (5.4) | 87.6 (5.1) |