TABLE II.

Interpretations of Feno test results for asthma diagnosis in nonsmoking individuals not taking corticosteroids^*

Feno level
<25 ppb (<20 in children aged 5–12 y)	25–50 ppb (20–35 in children aged 5–12 y)	>50 ppb (>35 in children aged 5–12 y)
• Recent or current corticosteroid use	• Evaluate in clinical context	• Eosinophilic airways inflammation likely
• Alternative diagnoses	• Consider other diagnoses	• Phenotype more likely to respond to ICS
• Phenotype less likely to benefit from ICS	• Consider other factors influencing result	• Allergic asthma
• Noneosinophilic asthma	• Eosinophilic asthma less likely	• Eosinophilic bronchitis
• COPD
• Bronchiectasis
• CF
• Vocal cord dysfunction
• Rhinosinusitis
• Smoking
• Obesity

CF, Cystic fibrosis; COPD, chronic obstructive pulmonary disease.

^*Reprinted with permission of the American Thoracic Society, ©2019 American Thoracic Society. Dweik RA, Boggs PB, Erzurum SC, Irvin CG, Leigh MW, Lundberg JO, et al. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FeNO) for clinical applications. Am J Respir Crit Care Med 2011;184:602–15. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society.