Diagnosis of occupational asthma from time point differences in serial PEF measurements

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.

Occupational asthma caused by samba (Triplochiton scleroxylon) wood dust in a professional maker of wooden models of airplanes: A case study

“…In our case 18% fall in FEV 1 was recorded in the 2nd and the 5th h after the SOCT. It is suggested by some evidence that in the case of a delayed reaction, FEV 1 fall ≥ 15% may be considered as positive SICT [31][32][33][34][35]. In the presented case occupational history of asthma symptoms, type of exposure, positive results of SPT to occupational allergens, the high level of bronchial hyperresponsiveness as well as significant decrease in FEV 1 and clinical symptoms with bronchial obstruction induced by the specific challenge test confirmed a positive reaction to the occupational allergen.…”

Specific inhalation challenge in the diagnosis of occupational asthma: consensus statement

“…This threshold value is arbitrary and a more rational approach would be to take into account the subject's variability in FEV1 when not exposed to the suspected agent. Such statistical methods are likely to be more sensitive than a fixed threshold value [50] but they require serial measurements of FEV1 on several (at least three) unexposed days in order to obtain an adequate estimate of the variance of the FEV1 [50,[104][105][106]. There is no consensus on the interpretation of PEF changes after SIC but their assessment should similarly take into consideration the natural (''unexposed'') variability of a subject's measurements; this is likely to be higher than the variability in measurements of FEV1.…”

Spirometry: step by step

“…These can be downloaded from www.occupationalasthma.com. Once the worker has performed the measurements, they can be inputted in a computer program, such as Oasys (Occupational Asthma System; freely available for download from www.occupationa lasthma.com) [10][11][12] for analysis ( fig. 5).…”