How many times per day should peak expiratory flow rates be assessed when investigating occupational asthma?
GROUND: Serial peak expiratory flow rate (PEF) recording has been advocated as a sensitive and specific means of confirming work related asthma. The optimum number of recordings per day to achieve the best between-reader and within-reader reproducibility and sensitivity/specificity ratio compared with the final diagnosis determined by specific inhalation challenges is unknown. METHODS: PEF recording was carried out every two hours in 74 subjects referred for possible occupational asthma. Specific inhalation challenges performed in a hospital laboratory or at the workplace (positive in 33 subjects and negative in 41) were considered the gold standard. The duration of monitoring at work and away from work was at least two weeks each. Graphs of PEF recordings were generated in four different ways: every two hours, four times/day, three times/day, and every morning and evening. The graphs were assessed by three readers in three different centres in a blind manner. Furthermore, one third of
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