title: 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).
  
  
  OBJECTIVE
  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.
authors.affiliation: Occupational Lung Disease Unit, Department of Respiratory Medicine, Birmingham Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS, UK.
authors.forename: W
authors.initials: W
authors.lastname: Anees
authors.forename: D
authors.initials: D
authors.lastname: Blainey
authors.forename: V C
authors.initials: VC
authors.lastname: Moore
authors.forename: K
authors.initials: K
authors.lastname: Robertson
authors.forename: P S
authors.initials: PS
authors.lastname: Burge
mesh_terms: D000328:Adult; D000382:Agricultural Workers' Diseases / Q000175:diagnosis; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D003937:Diagnosis, Differential; D004391:Dust; D002523:Edible Grain / Q000009:adverse effects; D005260:Female; D006801:Humans; D007509:Irritants / Q000633:toxicity; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000175:diagnosis* / Q000503:physiopathology; D016273:Occupational Exposure / Q000009:adverse effects; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D012680:Sensitivity and Specificity; D012767:Ships
chemical_list: D004391:Dust; D007509:Irritants