Occupational Asthma Reference

Anees W, Blainey D, Moore VC, Robertson K, Burge PS, Differentiating occupational asthmatics from non-occupational asthmatics and irritant-exposed workers, Occup Med, 2011;61:191-195,

Keywords: oasys,wasif score, mean resr-work, ppef, peak flow, grain, farmer, method

Known Authors

David Blainey, Essex, UK David Blainey

Sherwood Burge, Oasys Sherwood Burge

Wasif Anees, Oasys Wasif Anees

Vicky Moore, Oasys Vicky Moore

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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.

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Associated Questions

Registered users of this website have associated this reference with the following questions. This association is not a part of the BOHRF occupational asthma guidelines.

What are the sensitivity and specificity of serial measurements of peak flow in the diagnosis of occupational asthma?
burgeps When the mean PEF on workdays (starting with the first reading at work and continuing till the last reading before work on the next day, i.e. "day interpreted")is compared with the mean PEF on days away from exposure, a difference of 16 litres/min is outside the 95% CI for readings taken in non-asthmatics exposed to high levels of a respiratory irritant (grain). Taking a mean rest-work PEF >16 litres/min achieved a sensitivity of 68% and specificity 95% in indeendently diagnosed occupational asthmatics and asthmatic controls. An increase in diurnal variation on workdays of >7% (the upper 95% CI for aasthmatic controils) had a sensitivity of only 27% for the diagnosis of OA. The difference between maximum PEF on workdays and minimum PEF on rest days (as reported in Cote J, Kennedy S, ChanYeung M , Quantitative Versus Qualitative Analysis Of Peak Expiratory Flow In Occupational Asthma, Thorax, 1993; 48:48-51) had a sensitivity of <10% against non-occupational asthmatic controls

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