Occupational Asthma Reference

Burge CBSG, Moore VC, Pantin CFA, Robertson AS, Burge PS, Diagnosis of occupational asthma from time point differences in serial PEF measurements, Thorax, 2009;64:1032-1036,

Keywords:

Known Authors

Sherwood Burge, Oasys Sherwood Burge

Charles Pantin, Keele, UK Charles Pantin

Vicky Moore, Oasys Vicky Moore

Cedd Burge, Oasys Cedd Burge

Alastair Robertson, Selly Oak Hospital Alastair Robertson

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Abstract

Background
The diagnosis of occupational asthma requires objective confirmation. Analysis of serial measurements of peak expiratory flow (PEF) is usually the most convenient first step in the diagnostic process. A new method of analysis originally developed to detect late asthmatic reactions following specific inhalation testing is described. This was applied to serial PEF measurements made over many days in the workplace to supplement existing methods of PEF analysis.

Methods
236 records from workers with independently diagnosed occupational asthma and 320 records from controls with asthma were available. The pooled standard deviation for rest day measurements was obtained from an analysis of variance by time. Work day PEF measurements were meaned into matching 2-hourly time segments. Time points with mean work day PEF statistically lower (at the Bonferroni adjusted 5% level) than the rest days were counted after adjusting for the number of contributing measurements.

Results
A minimum of four time point comparisons were needed. Records with >=2 time points significantly lower on work days had a sensitivity of 67% and a specificity of 99% for the diagnosis of occupational asthma against independent diagnoses. Reducing the requirements to >=1 non-waking time point difference increased sensitivity to 77% and reduced specificity to 93%. The analysis was only applicable to 43% of available records, mainly due to differences in waking times on work and rest days.

Conclusion
Time point analysis complements other validated methods of PEF analysis for the diagnosis of occupational asthma. It requires shorter records than are required for the Oasys score and can identify smaller changes than other methods, but is dependent on low rest day PEF variance.

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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?
Cedd Burge A minimum of four time point comparisons were needed (43% of available records - but improvable if collecting data prospectively). Sensitivity of 67% and a specificity of 99%.
What are the minimum criteria for serial measurements of peak flow to maintain a high degree of diagnostic accuracy?
Cedd Burge A minimum of four time point comparisons were needed (only 43% of available records). This equates to a minimum of four readings per day for 3 work and 3 rest days, as long as readings taken at the same times every day. 6-8 readings per day for 5 work days (1 week) and 4 rest days (2 weekends) should be requested from patients. Patients need to wake up at similar times on work and rest days.

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