AbstractObjectiveInternational guidelines recommend measuring fractional exhaled nitric oxide (FeNO) during a single slow exhalation with a constant flow of 50 ml/sec. We developed a new algorithm to compute FeNO at 50 ml/sec from tidal breathing measurements. The main objective is to assess the correlation and agreement of this algorithm with the conventional single breath FeNO measurements.MethodsWe recruited children aged 6–18 years, who performed both a single breath and a tidal breathing FeNO measurement in random order. Both maneuvers were performed on the Eco Medics NO‐analyser (Eco Physics AG, Duernten, Switzerland).ResultsWe included 109 patients between January 2011 and April 2011. Geometric mean (95% CI) FeNO values did not differ significantly between single breath and tidal breathing technique: 21.0 (17.7–24.8) ppb and 20.0 (17.0–23.6) ppb (P = 0.18), respectively. We found an excellent intraclass correlation coefficient of 0.96 (0.94–0.97) and moderate agreement with a mean difference of 4% (95% limits of agreement −43% and +90%).ConclusionTidal breathing FeNO values could be transformed with a new algorithm to match single breath FeNO at a constant flow of 50 ml/sec. This algorithm opens the way to standardized FeNO measurements in preschool children and uncooperative patients. Pediatr Pulmonol. 2014; 49:15–20. © 2013 Wiley Periodicals, Inc.