The Usefulness of FEF(25–75) in Predicting Airway Hyperresponsiveness to Mannitol

BACKGROUND AND OBJECTIVE: Despite the usefulness of airway hyperresponsiveness (AHR) testing in diagnosing and monitoring asthma, it is challenging to perform in a real-world setting. Forced expiratory flow between 25% and 75% of vital capacity (FEF(25–75)), a pulmonary measurement that can be obtained easily during routine spirometry, represents the status of medium-sized and small airways. However, the performance of FEF(25–75) in predicting AHR has not been well elucidated. Therefore, we investigated whether FEF(25–75) can predict AHR to mannitol. METHODS: We performed a retrospective cohort study of 428 patients who visited a single clinic due to cough, wheezing, or dyspnea. All patients underwent spirometry with a mannitol provocation test. We compared the area under the curve (AUC) of the percentage of the predicted values of FEF(25–75) (FEF(25–75) %pred) with that of forced expiratory volume in 1 second (FEV(1)%pred), FEV(1)/forced vital capacity (FVC), and FEF(25–75)/ FVC for predicting AHR. RESULTS: The rate of AHR to mannitol was 20.3%. In the overall study population, the AUC of FEF(25–75) %pred for predicting AHR (0.772; 95% confidence interval [CI], 0.729–0.811) was significantly higher than that of FEV(1)%pred (0.666; 95% CI, 0.619–0.710; p < 0.001), FEV(1)/FVC (0.741; 95% CI, 0.697–0.782; p = 0.047), and FEF(25–75)/FVC (0.741, 95% CI = 0.696–0.782, p = 0.046). The sensitivity, specificity, positive predictive value, and negative predictive value of FEF(25–75) %pred <81% for predicting AHR in the overall study population were 77.0% (95% CI = 66.8–85.4%), 63.9% (95% CI = 58.6–69.0), 35.3%, and 91.6%, respectively. When we restricted the study group to subjects with normal lung function, the results were similar. CONCLUSION: Our results indicate that FEF(25–75) %pred can be used as a surrogate for predicting AHR in patients with respiratory symptoms.