PEF analysis requiring shorter records for occupational asthma diagnosis

The Oasys programme plots serial peak expiratory flow (PEF) measurements and produces scores of the likelihood that the recordings demonstrate occupational asthma. We have previously shown that the area between the mean workday and rest day PEF curves [the area between the curves (ABC) score] has a sensitivity of 69% and specificity of 100% when plotted from waking time using a cut-off score of 15 l/min/h.

To investigate the minimum data requirements to maintain the sensitivity and specificity of the ABC score.

A total of 196 sets of measurements from workers with occupational asthma confirmed by methods other than serial PEFs and 206 records from occupational and non-occupational asthmatics who were not at work at the time of PEF monitoring were analysed according to their mean number of readings per day. Measurements from work and rest days were sequentially removed separately and the ABC score calculated at each reduction. The sensitivity and specificity of the ABC score (using a cut-off of 15 l/min/h) was calculated for each duration.

Two-hourly measurements (approximately 8 readings per day) with eight workdays and three rest days had 68% sensitivity and 91% specificity for occupational asthma diagnosis. As readings decreased to or=15 workdays were required to provide a specificity above 90%.

To be sensitive and specific in the diagnosis of occupational asthma, the ABC score requires 2-hourly PEF measurements on eight workdays and three rest days. This is a short assessment period that should improve patient compliance.