Background: Older guidelines recommend that fractional exhaled nitric oxide (FeNO) should be checked more than twice during the same session to confirm an asthma diagnosis. Recent studies show the excellent reproducibility of FeNO measurements.
Objective: We aimed to determine whether repeated FeNO measurements during the same session are necessary for asthma screening.
Methods: We retrospectively reviewed the electronic medical records of adult outpatients who visited the respiratory medicine department for diagnosis of asthma and assessed FeNO measurements obtained from June 2016 to July 2017.
Results: Of the 132 patients enrolled, 79 (59.8%) were diagnosed with asthma. Repeated FeNO measurements taken during the same session showed high reproducibility (intraclass correlation coefficient >0.9; P<.001) and a strong correlation (Pearson coefficient >0.9; P<.001), although reproducibility and correlation were slightly weaker in patients with low FeNO values. The value of repeated measurement was not significant; however, the second FeNO measurement was significantly higher than the first measurement in patients with the worst and best lung function. The predictive power of the first measurement of FeNO (sensitivity, 80.5%; specificity, 85.1%) was not inferior to the second (sensitivity, 76.6%; specificity 85.1%). The same was true of the geometric mean of the two.
Conclusion: Repeated FeNO measurement during the same session is not essential for asthma screening in cases where the first acceptable FeNO measurement is performed using the proper method.

Key words: Asthma, Fractional exhaled nitric oxide, Repeated measurements