FeNO measurement
FeNO was measured online by using the single-breath technique with a portable analyzer(NIOX-MINO, Aerocrine, Stockholm, Sweden) according to guidelinesand expressed as parts per billion.12, 22Measurements were performed before lung function tests. After inhalation of nitric oxide–free air for total lung capacity, the measurement was performed while the patient exhaled at a constant flow rate of 50 ml/s. In the American Thoracic Society guideline, FeNO mesurements of children with asthma were recommended to be evaluated with the cut-off levels of <20 ppb and >35 ppb, which is probably to mean less and more likely for eosinophilic inflammation and corticosteroid response.12