Occupational asthma: validity of monitoring of peak expiratory flow rates and non-allergic bronchial responsiveness as compared to specific inhalation challenge.

The sensitivity and specificity of monitoring peak expiratory flow rates (PEFR) and bronchial responsiveness to the provocative concentration of histamine or methacholine (PC20) has been determined as compared to specific inhalation challenges in the diagnosis of occupational asthma. A prospective study of 61 subjects referred for occupational asthma to various agents was performed. PEFR was assessed every 2 h during a period away from work for at least 2 weeks. The period at work was 2 weeks, or less if there was increased symptomatology or marked changes in PEFR. At least one PC20 assessment was obtained at work and away from work. Graphs of PEFR and PC20 values were interpreted in blind fashion by three experienced readers. There was complete agreement among the three in 54 out of 61 instances (78%). Twenty five out of 61 subjects (41%) had positive specific inhalation challenges. The best index for comparing results of PEFR with specific inhalation challenges was the visual analysis of PEFR with sensitivity and specificity of 81% and 74%. All of the numerical indices were significantly less satisfactory. We conclude that visual analysis of PEFR is an interesting tool for investigating occupational asthma, although sensitivity and specificity values do not seem satisfactory enough to warrant using it alone.