Measurement of fractional exhaled nitric oxide
FeNO was measured using a handheld electrochemical analyzer (NIOX MINO®; Aerocrine AB, Sweden) according to the 2005 American Thoracic Society/European Respiratory Society (ATS/ERS) recommendations for standardized single-breath online measurement.18 Children were prevented from eating, drinking, and exercising at least 1 hour before the FeNO measurement; nitrate or nitrate-containing foods were avoided the night prior to testing.