Occupational Asthma Reference

Bright P, Burge PS, Does the delay in the time of the first reading of the day produce falsely positive records in patients performing serial peak flow for the diagnosis of occupational asthma?, Thorax, 1996;51 Suppl 3:A71,

Keywords: OASYS-NN, PEF, quality, waking,

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Sherwood Burge, Oasys Sherwood Burge

Phil Bright, Oasys Phil Bright

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Later recording of peak expiratory flow (PEF) after waking on rest days has resulted in falsely positive assessment of occupational asthma on serial PEF records (Venables, Thorax 44:760-761). We have investigated the times of the first PEF measurements of the day in 43 workers with suspected occupational asthma, comparing work and rest days. We have also examined the effect of timing of first reading on subjective and computer analysis (OASYS-NN) assessment of work-related changes in the PEF record. Records were kept for a minimum of 21 days (mean 43.5 days) with mean 7.9 readings per day. The time of the first reading was significantly later on rest than work days, 08.27 (95% CI 08.08, 08.50) vs 06.56 (95% CI 06.28, 07.25) respectively (paired t test, p<0.001). There was a weak and insignificant correlation between the time of the first reading and the overall score for work-related effects in the serial PEF record for OASYS-NN, r=0.20 (95% CI -0.18, 0.35), for subjective assessment r=0.18 (95% CI -0.19, 0.34). The correlation was therefore lower for records least likely to show an occupational effect, when false positive assessments are potentially a problem.

This suggests that in clinical practice the effect of late first reading on rest days is unlikely to alter the assessment of work-related changes in the serial PEF record using OASYS-NN.

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