Comparison of peak expiratory flows and FEV1 in assessing immediate asthmatic reactions due to occupational agents

Background: FEV1 is more sensitive than PEF in assessing late asthmatic res ponses (LAR) after specific inhalation challenges (SIC) with occupational a gents. As immediate asthmatic reactions (IAR) mainly involve proximal airwa ys, PEF may, however, be as valid as FEV1. Methods: Thirty-seven subjects who experienced an immediate fall in FEV1 of greater than or equal to 20% during SiC with occupational agents and 20 su bjects with fall of less than or equal to 10% in FEV1 were included. Both F EV1 and PEF were measured in a random order every 10 min for 1 h after expo sure. We corrected PEF (PEFc) for inaccuracies of the mini-Wright meters by the Miller equation. Results: Maximum changes in PEFc (30+/-11%) were not significantly differen t from changes in FEV1 (27+/-5%) (P=0.13). Their timings after exposure wer e 14+/-11 min and 17+/-17 min. respectively (P=0.4). High sensitivity (92%) , specificity (95%), accuracy (93%), and positive predictive value (97%) we re found for a 20% fall in PEFc to detect a significant IAR. Results were b etter and not influenced by meter inaccuracies with a cutoff point of 15% c hange in noncorrected PEF (PEFnc). An absolute decrease in PEF of 70 l/min gave a good discrimination between reactions with and without an asthmatic response. Conclusions: PEF is as satisfactory as FEV1 for detecting a significant IAR after exposure to an occupational agent if one considers a cutoff point of 1) 15% fall in PEF 2) 20% fall in PEFc 3) 20% fall and/or 70 l/min decrease in PEFnc.