Reference values and factors associated with exhaled nitric oxide: U.S. youth and adults

Normative values for fractional exhaled nitric oxide (FeNO) and the associated co-factors are important in understanding the role of FeNO as a biomarker in airway disease. The objective of this study is to establish reference FeNO values for youth and adult asymptomatic, lifetime nonsmokers in the United States, and to describe the factors affecting these levels.

Cross-sectional analyses of the National Health and Nutrition Examination Survey from 2007 to 2010. The analytic sample consisted of 4718 youth and adults, ages 6-79 years, who were lifelong nonsmokers, and free of asthma, and other respiratory conditions and symptoms. Loge FeNO values were used as dependent variables to test associations of demographic and health related-covariates. Multivariable regression models were used to assess the independent effect and covariate-adjusted contribution of the factors.

The geometric mean FeNO level was 8.3, 12.1, and 16.2 ppb for males 6-11, 12-19, and 20-79 years, and 8.4, 10.9, and 12.6 ppb for females in the corresponding age groups. Overall, FeNO levels increased with increasing age (p < 0.001), and height (p < 0.001). In all age groups, FeNO levels were positively associated with eosinophil counts, and with testing in the morning. Among youths 6-11 and 12-19 years, non-Hispanics whites had lower FeNO values than non-Hispanic blacks and Hispanic youths. No race-ethnic difference in FeNO levels was evident for adults 20-79 years. Among adolescents and adults, FeNO levels were higher for males than for females, controlling for all other factors.

These reference values and associated attributes in youths and adults are useful in evaluating the role of FeNO in airway diseases.