Occupational asthma (scope: sensitizer induced, and basics of workplace provocation and specific bronchial provocation)

‘Workplace’ provocation is a cornerstone of diagnosis in occupational asthma; indeed it is, arguably, a test that should be considered in every potential case of the disease. The simplest approach is through the use of serial peak flow measurement undertaken at and away from work with a careful comparison of readings across different periods. If done carefully, such a technique achieves a sensitivity and specificity close to 80%.  Other methods, using for example cross-shift measurements of FEV1 or bronchial reactivity, are generally more difficult to arrange and in most centres have a lower diagnostic value.  In contrast, specific inhalation challenge (SIC) is a ‘gold standard’ diagnostic test that is, in most settings, seldom either applied or required. In any case, its complexity, heavy use of resources and expense mean that few centres offer such a service. Where it is practised, outside the legislative requirement of some jurisdictions, it is usually reserved for cases where the diagnosis cannot be made using simpler approaches or where the aetiological role of a previously unrecognised workplace agent is being investigated. Access to such a service is thus valuable but unnecessary in every diagnostic centre. The practise of SIC is semi-standardised. Most centres use a ‘Pepys’ method for delivering the antigen in an attempt to replicate, under experimental conditions, exposure in the workplace; a few others have adopted devices that aim to ensure a continuously measurable delivery of agent to the breathing zone. Placebo-controlled exposures, with at least single-blinding, are widely used; and responses generally monitored through repeated measurement of FEV1 and, helpfully, non-specific bronchial reactivity. With care, false positive results should be very few; false negative tests may reflect insufficient provocation or the use of the wrong agent. Safety is paramount, since SIC is not without risk. In some contrast, ‘workplace’ challenges.