The FEF25-75% and the clinical diagnosis of asthma

Nonspecific bronchial provocation testing is clinically useful in the evaluation of patients with symptoms suggestive of asthma. Testing is usually reserved for those with normal or near normal baseline spirometry. Although bronchial provocation testing is safe and widely available, the protocol is time consuming and not without expense. It has been reported that a reduced FEF25-75% in the context of an otherwise normal spirogram suggests that asthma should be considered. To evaluate this suggestion, we compared the baseline FEF25-75% (expressed as percent of predicted) with the results of the subsequent methacholine bronchial provocation test in 205 consecutive patients referred for testing. The mean baseline FEF25-75% in the 112 patients with normally responsive airways (ie, a negative bronchial provocation test) was 95.4 +/- 27.5%. In the 93 patients with a positive bronchial provocation test, the mean FEF25-75% was 77.6 +/- 27.2%. The mean FEF25-75% in those with hyperresponsive airways was significantly lower (t = 4.616, P < .0001). Of those patients with a positive bronchial provocation test, there was no significant correlation, however, between the baseline FEF25-75% and the degree of bronchial hyperresponsiveness as assessed by the PC20FEV1 (r = .154, P = .141). When a significant reduction in FEF25-75% was defined as less than 60% of predicted, the sensitivity of the prediction rule was 25.8%, the specificity was 92.0%, the positive predictive value was 72.7%, and the negative predictive value was 60.0%. From these results, we conclude that the FEF25-75% derived from simple spirometry may be useful in predicting the presence or absence, but not the degree, of bronchial hyperresponsiveness.