The Usefulness of FEF_25-75 in Predicting Airway Hyperresponsiveness to Mannitol

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.

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 (FEV₁%pred), FEV₁/forced vital capacity (FVC), and FEF_25-75/ FVC for predicting AHR.

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 FEV₁%pred (0.666; 95% CI, 0.619-0.710; p < 0.001), FEV₁/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.

Our results indicate that FEF_25-75 %pred can be used as a surrogate for predicting AHR in patients with respiratory symptoms.