Study population
Between January 2012 and January 2014, the patients with asthma, aged 6-18 years old, were invited to the study while their routine asthma follow-up at the outpatient clinic of Pediatric Allergy Department of a tertiary research and training hospital. The must inclusion criteria was to have physician diagnosed asthma based on criteria recommended by the GINAand the US National Asthma Education and Prevention Program.1, 3 The others were to be adherent to their asthma treatment, able to perform FeNO and spirometry measurements properly according to the guidelines. Children were excluded if they did not meet all inclusion criteria or had comorbid diseases other than allergic diseases, if they were having an acute attack or respiratory infection which were unfavorable for FeNO and spirometry tests. The study was approved by the Institutional Review Board. Parent/caregiver provided informed consent and writtten assent was taken from children older than 6 years old.