Differentiating occupational asthmatics from non-occupational asthmatics and irritant-exposed workers

Abstract

BACKGROUND: Serial peak expiratory flow (PEF) records have been recommended as a first-line investigation in workers suspected as having occupational asthma (OA). AIMS: To determine which PEF variability index best differentiates workers with OA from non-occupational asthmatics and unaffected irritant-exposed workers. METHODS: PEF was measured at least four times daily for at least 3 weeks in three groups of subjects: (i) forty healthy grain-exposed farmers and dockers, (ii) forty-two consecutive workers with independently confirmed OA and (iii) forty-eight non-occupational asthmatics. Indices of PEF variability were compared between groups. RESULTS: The difference in mean PEF between rest and work periods best separated the occupational asthmatic workers from the others. The upper 95% confidence limit of this index for grain-exposed workers was 2.8% of predicted PEF (16 l/min) and 3.3% (15 l/min) for non-occupational asthmatics. Sensitivity for diagnosing OA using this index was 70%. An increase in diurnal variation on workdays of >7% had a sensitivity of only 27% for the diagnosis of OA. The difference between maximum PEF on workdays and minimum PEF on rest days had a sensitivity of <10% against non-occupational asthmatic controls. CONCLUSIONS: Difference in mean PEF between workdays and rest days is the best simple index for differentiating subjects with OA from those with non-OA or irritant-exposed healthy subjects. Differences >16 l/min are unlikely to be due to significant irritant exposure in healthy workers.