AUC: area under the curve; ROC: receiver operating characteristic; FENO: fractional exhaled nitric oxide; FEV1: forced expiratory volume in 1 second; FVC: forced vital capacity; FEF: forced expiratory flow; FEF50%: FEF at 50% of FVC; FEF70%: FEF at 70% of FVC; FEF25%-75%: FEF at 25% to 75% of FVC.