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DOI:    [Accepted]
Measurement of Fractional Exhaled Nitric Oxide in Adults: Comparison of Two Different Analyzers (NIOX VERO® and NObreath®)
Sung-Yoon Kang, Sang Min Lee, Sang Pyo Lee, M.D., Ph.D.
Division of Pulmonology and Allergy, Department of Internal Medicine, Gachon University Gil Medical Center, Incheon, Korea
Correspondence:  Sang Pyo Lee, Tel: +82-32-460-3204, Fax: +82-32-469-4320, 
Received: 16 November 2020   • Revised: 31 December 2020   • Accepted: 10 March 2021
Fractional exhaled nitric oxide (FeNO) is a recognized marker for eosinophilic airway inflammation and treatment decisions for corticosteroid response. Our study aimed to compare two FeNO analyzers and derive a conversion equation for adults.
We included 99 participants with chronic cough and difficulty in breathing who attended outpatient clinics. They underwent concurrent FeNO measurement randomly using NIOX VERO® (Circassia AB, Solna, Sweden) and NObreath® (Bedfont, Kent, UK). We compared the two devices according to values, correlation and agreement. We then formulated an equation to convert FeNO values measured by NObreath® into those obtained by NIOX VERO®.
The mean age was 51.2 ± 17.1 years, with female predominance (58.6%). Approximately 60% of the participants had asthma. The median (interquartile range) FeNO level measured by NIOX VERO® (27, 15–45) was significantly lower than that by NObreath® (38, 22–58, p < 0.001). FeNO level measurement had a strong positive correlation between the devices (r = 0.779, p < 0.001). Additionally, Bland–Altman plots and intraclass correlation coefficient demonstrated a good strength of agreement. Using linear regression, we derived the following conversion equation: natural log (Ln) (NObreath®) = 0.728 × Ln (NIOX VERO®) + 1.244.
The values of these two FeNO analyzers were in good agreement and had positive correlations. Our proposed conversion equation could help assess the data obtained by these two analyzers.
Key Words: exhaled, nitric oxide, biomarkers, respiratory

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