Specific inhalation challenge (SIC) is the diagnostic reference standard for occupational asthma, however the significance of a positive test is doubtful unless it can be reproduced by usual work exposures. We have compared the timing and responses during SIC in hospital to Oasys analysis of serial PEF during usual work exposures.
All workers with a positive SIC to occupational agents between 2006 and 2015 were asked to measure PEF 2-hourly from waking to sleeping for 4 weeks during usual occupational exposures. Responses were compared between the laboratory challenge and the real-world exposures at work.
All 53 workers with positive SIC were included. 49/53 had records suitable for Oasys analysis, 14 requiring >1 attempt, all confirmed occupational work-related changes in PEF. There was a significant correlation between immediate SIC reactors and deterioration within the first 2 hours of starting work with early recovery, and between late SIC reactors and a delayed start to workplace deterioration and delayed recovery. Dual SIC reactions had features of immediate or late SIC reactions at work rather than dual reactions.
The concordance of timings of reactions during SIC and at work provide further validation for the clinical significance of each test.