Results of pre-/postchallenge histamine reactivity, bronchial challenge and occupational asthma system (OASYS)-2 score
| Case | Previous histamine PD20 µmol | Prechallenge histamine PD20 µmol | Postchallenge histamine PD20 µmol | % Maximum immediate fall in FEV1 | % Maximum late fall in FEV1 | OASYS-2 score |
| 1 | >8 | >8 | >8 | −45 | −48 | 3.8 |
| 2 | 1.5 | >8 | >8 | −27¶ | −6¶ | 2.88 |
| 3 | >8 | Not done | Not done | −14 work challenge | Not done | See text |
| 4 | >4800 µg methacholine | 125 µg methacholine | 70 µg methacholine | −15 (NCl3) −41 (formaldehyde) | 0 (NCl3) −4.1 (formaldehyde) | 4.00 |
#: The prechallenge histamine test was performed within 2 days of being at work in case 3, but in case 2 the worker had relocated to a library 1-yr previously. The worker previously had a positive histamine challenge when seen in the clinic whilst working as a lifeguard (2 days prior to the test) with a provocative dose causing a 20% fall in the forced expiratory volume in one second (FEV1) (PD20) of 1.5 µmol
¶: The worker had two challenges to nitrogen trichloride with 30 min exposure on consecutive days. The data shown in the table are for the second day following a 30-min exposure. On the first day, the maximum immediate reaction fall in FEV1 was −17% at 20 min and maximum late reaction at 40 min was −15.