Occupational Asthma Reference
Moore V, Jaakkola M, Burge CBSG, Robertson A, Pantin C, Burge PS,
Is diurnal PEF variation sensitive and specific for the diagnosis of occupational asthma?,
Eur Respir J,
Keywords: Oasys, diurnal variation, oa, diagnosis, method,uk
Serial peak expiratory flow (PEF) measurements on days at and away from work are recommended as the first step in the objective confirmation of occupational asthma. This study aims to identify the best cut off for the difference between diurnal variation (DV) at work and DV at rest (days off work) that is both sensitive and specific for diagnosing occupational asthma.
Mean 2-hourly PEFs were plotted separately for work days and rest days for 109 workers with occupational asthma and 117 control asthmatics. DV at work and rest was calculated by the Oasys program from records containing = 4 day shifts, = 4 rest days and = 6 readings per day. DV at work minus DV at rest was calculated by% predicted and% mean. Patients were randomly divided into 2 datasets (analysis and test sets). Receiver operator characteristic curve analysis determined a cut off point from Set 1 that best identified those with occupational asthma, which was then tested in Set 2.
ROC curve analysis gave an area under the curve of 0.68 (set 1) and 0.69 (set 2) analysed as% mean and 0.70 (set 1 and set 2) analysed as% predicted. Table 1 shows the sensitivity and specificity of DV at different cut offs in set 2.
Table 1 Set 2: DV at work - DV at rest (% predicted) Set 2: DV at work - DV at rest (% mean)
Cut off (%) Sensitivity (%) Specificity (%) Sensitivity (%) Specificity (%)
7.6 20 100 28 95
3.4 44 95 54 90
1.4 63 83 65 71
0.6 67 57 69 57
A 1.4% higher DV at work compared to rest has the best combined sensitivity and specificity for the diagnosis of occupational asthma. Although the sensitivity and specificity are acceptable, they are somewhat lower than other scores calculated by the Oasys program.
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