THE FEF(25-75-PERCENT) 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 spirome try. Although bronchial provocation testing is safe and widely availab le, the protocol is time consuming and not without expense. It has bee n reported that a reduced FEF(25-75%) in the context of an otherwise n ormal spirogram suggests that asthma should be considered. To evaluate this suggestion, we compared the baseline FEF(25-75%) (expressed as p ercent of predicted) with the results of the subsequent methacholine b ronchial provocation test in 205 consecutive patients referred for tes ting. The mean baseline FEF(25-75%) in the 112 patients with normally responsive airways tie, a negative bronchial provocation test) was 95. 4 +/- 27.5%. In the 93 patients with a positive bronchial provocation test, the mean FEF(25-75%) was 77.6 +/- 27.2%. The mean FEF(25-75%) 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 basel ine FEF(25-75%) and the degree of bronchial hyperresponsiveness as ass essed by the PC(20)FEV(1) (r = .154, P = .141). When a significant red uction in FEF(25-75%) was defined as less than 60% of predicted, the s ensitivity 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 FEF(25-75%) derived from simple spirometry may be useful in predicting the presen ce or absence, but not the degree, of bronchial hyperresponsiveness.