Diagnosis of occupational asthma from serial measurements of forced expiratory volume in 1 s (FEV1) using the Area Between Curves (ABC) score from the Oasys plotter.

The diagnosis of OA requires objective confirmation. Unsupervised serial FEV1 measurements are more difficult to obtain reliably than measurements of peak expiratory flow, which are likely to remain the standard for general use. A FEV1 ABC score >0.056 L/hour provides a valid cut-off for those who wish to use FEV1 rather than peak expiratory flow.