Introduction: Specific inhalation challenge (SIC) is the reference standard for the diagnosis of occupational asthma, however the significance of a positive test is doubtful unless work exposure causes measurable changes in lung function. We have used Oasys analysis of serial PEF at home and work (with a specificity of >90%) to identify occupational asthma, and have used these to validate the specificity of SIC testing with non-standard agents.
Methods: This is a retrospective survey of all workers with positive SIC to occupational agents contributing to the EAACI survey. They were asked to measure PEF 2-hourly from waking to sleeping for 4 weeks before SIC testing with realistic exposures. Inadequate PEF records were repeated. The hourly patterns of response were compared between SIC and PEF record.
Results: 52 consecutive workers with positive SIC to a wide range of mostly unusual occupational agents were included. Records suitable for Oasys analysis were obtained in 48/52, 14 requiring >1 attempt. 48/48 confirmed occupational work-related changes in PEF by at least 1 of the Oasys evaluations (Oasys score, ABC or timepoint). There was a strong association between the timings of response at work and during SIC (χ2 =15 p<0.001), Table 1.
Relationship between pattern of reaction at work from serial PEFs and SIC.
|Oasys pattern (unclassifiable in 3)||Immediate or dual||Late or dual|
|Immediate or flat||24||6|
Conclusion: Positive SIC testing with realistic occupational exposures does not produce false positive tests in our hands, and has identified many unusual and novel causes of occupational asthma.