Clinical and functional characteristics at initial assessment
| Occupational asthma | Subjects with negative SIC | |
| Subjects n | 86 | 71 |
| Asthma before employment n (%)¶ | 17 (20) | 5 (7) |
| Duration of exposure before onset of workrelated asthma symptoms month# | 82 (26–164) | 93 (20–195) |
| Duration of asthma before diagnosis month# | 46 (24–77) | 36 (19–68) |
| Removal from work before SIC | 46 (53) | 40 (56) |
| Time lapse from last work exposure to SIC month# | 0.6 (0.1–16.5) | 2 (0.1–17.0) |
| Duration of followup month# | 40 (28–67) | 47 (29–66) |
| Asthmaseverity score# | 8 (5–9) | 7 (5–8) |
| FEV1 % pred# | 93 (83–102) | 93 (81–100) |
| FEV1 <80% pred | 12 (14) | 17 (24) |
| FEV1 /FVC %# | 78 (71–81) | 75 (69–81) |
| Histamine PC20, mg·mL−1#,† | 0.72 (0.09–2.57) | 1.46 (0.23–5.27) |
| ≥16 mg·mL−1 | 6 (7) | 5 (7) |
| 2–16 mg·mL−1 | 19 (22) | 23 (32) |
| 0.25–2 mg·mL−1 | 32 (37) | 24 (34) |
| <0.25 mg·mL−1 | 29 (34) | 19 (27) |
Data are presented as n (%) or n (range)
SIC: specific inhalation challenge
FEV1 : forced expiratory volume in one second
FVC: forced vital capacity
PC20: provocation concentration causing a 20% fall in FEV1
#: median (25th–75th percentiles)
¶: p=0.022
†: 0.021 comparing subjects with occupational asthma and those with negative SIC