Reference Ranges and Determinant Factors for Fractional Exhaled Nitric Oxide in a Healthy Saudi Adult Population

BACKGROUND: Fractional exhaled nitric oxide (FENO) has emerged as a promising marker in respiratory research. The aim of this study was to determine the reference range values of FENO for healthy Saudi adults and the factors associated with FENO levels. MATERIAL/METHODS: This cross-sectional study was conducted at the Department of Physiology, King Saud University, Riyadh, Saudi Arabia, from January 2016 to August 2017. A total of 429 healthy Saudi adults were initially recruited. The final selection included 412 participants, consisting of 307 men and 105 women. FENO measurements were performed according to the current recommendations of the American Thoracic Society. RESULTS: We observed that the FENO levels of women were significantly lower than those of men (18.6 vs. 21.3, P=0.009). In women, the measured FENO ranged from 5.7 ppb to 42 ppb, and in men from 5.0 ppb to 55.0 ppb. The mean FENO level in the entire study population was 20.6, with a range of 5.0 ppb to 55.0 ppb. The difference became non-significant when we calculated the FENO after adjusting for body surface area by different percentile distributions. Multiple linear regression analysis showed that body surface area and weight were significant predictors of FENO levels. CONCLUSIONS: In this study, FENO levels were significantly affected by demographic variables. Therefore, it is important to consider the factors influencing FENO values to make a valid clinical interpretation.