Normal FeNO Values in Healthy Adults

Reference Values Based on Population Studies

The American Thoracic Society guidelines establish that normal FeNO ranges depend significantly on whether you account for atopy and other confounding factors, with the upper limit of normal being <35 ppb in the general healthy population 1, 2, 3, 4
When outliers are removed, the upper limit reduces to <25 ppb, according to the American Thoracic Society guidelines 1, 2, 3, 4
The American Thoracic Society guidelines also state that when both outliers and atopic individuals are excluded, the upper limit further reduces to <20 ppb 1, 2, 3, 4

Sex differences: Males typically have FeNO values 20-30% higher than females, as reported by the American Thoracic Society 1, 2, 3, 4
Atopy status: Atopic individuals have substantially higher values, with non-atopic males (nonsmokers) having FeNO values of 9.5-47.4 ppb, and atopic males (nonsmokers) having FeNO values of 11.2-56.5 ppb, according to the American Thoracic Society 5
Smoking: Current smokers have significantly lower values, with reductions of approximately 20-40% compared to nonsmokers, as reported by the American Thoracic Society 5, 1, 2, 3, 4
Age and height: Both influence FeNO values, particularly in children under 12 years, though the effect is less consistent in adults, according to the American Thoracic Society 5, 6

The American Thoracic Society recommends using clinically relevant cut-points rather than population reference values because of substantial overlap between healthy individuals and those with stable asthma 5, 6
Low FeNO (<25 ppb in adults): Eosinophilic inflammation unlikely, as recommended by the American Thoracic Society 5
High FeNO (>50 ppb): Eosinophilic inflammation likely present, according to the American Thoracic Society 5