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Interpreting FeNO

Measuring FeNO helps Healthcare Providers to optimize the use of steroids.1-3

Determining responsiveness to anti-inflammatory therapy

An important benefit of measuring fractional exhaled nitric oxide (FeNO) is its ability to identify patients who are likely to benefit from treatment with corticosteroids.1

It has been shown that FeNO predicts the likelihood of steroid responsiveness more consistently than spirometry, bronchodilator response, peak flow variation, or airway hyperresponsiveness to methacholine.4-6

Overview of clinical guideline to interpretation of FeNO levels1

For the management of patients with suspected or diagnosed asthma

FeNO levels and inflammation
Adults <25 25-50 >50
Children (<12 years) <20 20-35 >35
Th2-driven inflammation Unlikely Likely Significant
Diagnosis Considerations
Interpretation with respect to
steroid response
  • - Unlikely to respond to corticosteroids
  • - May respond to corticosteroids (interpret cautiously in clinical context)
  • - Highly likely to respond to corticosteroids
Guide to diagnosis
  • - Consider alternative diagnosis including chronic cough, vocal cord dysfunction, non-allergic asthma, GERD
  • - Be cautious, but consider asthma
  • - Monitor change in FeNO over time
  • - Supports a diagnosis of asthma
Monitoring (in patients with diagnosed asthma)
Symptoms present
  • - Consider alternative diagnosis
  • - Not likely to respond to increased ICS dose
  • - Consider rechecking in 2-3 months
  • - Consider persistent allergen exposure
  • - Check adherence
  • - Consider increasing ICS dose
  • - Consider steroid resistance
  • - Consider rechecking in 2-3 months
  • - Consider persistent allergen exposure
  • - Check adherence and inhaler technique
  • - Consider increasing ICS dose
  • - Consider other anti-inflammatory therapy
  • - Consider rechecking in 2-4 weeks
Symptoms absent
  • - Adequate ICS dose
  • - Good adherence
  • - If on ICS, consider decreasing dose or discontinuing ICS
  • - Consider rechecking in 2-4 weeks
  • - Adequate ICS dosing
  • - Good adherence
  • - Monitor change in FeNO
  • - Consider rechecking in 2-3 months
  • - ICS withdrawal or dose reduction may result in relapse
  • - Poor adherence or inhaler technique
  • - Consider rechecking in 2-3 months

*Interpretations of levels based on patient having symptoms (cough and/or wheeze and/or shortness of breath) present during the past 6+ weeks. Smoking has been shown to reduce FeNO levels.7


References: 1. Dweik RA, Boggs PB, Erzurum SC, et al; on behalf of the American Thoracic Society Committee on Interpretation of Exhaled Nitric Oxide Levels (FeNO) for Clinical Applications. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FeNO) for clinical applications. Am J Respir Crit Care Med. 2011;184:602-615. 2. Price DB et al. Fractional Exhaled Nitric Oxide as a Predictor of Response to Inhaled Corticosteroids in Patients With Non-Specific Respiratory Symptoms and Insignificant Bronchodilator Reversibility: A Randomised Controlled Trial. Lancet Respir Med. 2018 6 (1):29-39 3. Hanania NA et al. Measurement of fractional exhaled nitric oxide in real-world clinical practice alters asthma treatment decisions. Ann Allergy Asthma Immunol. 2018 120(4):414-418. 4. 4. Knuffman JE et al; for the Childhood Asthma Research and Education Network of the National Heart, Lung, and Blood Institute. Phenotypic predictors of long-term response to inhaled corticosteroid and leukotriene modifier therapies in pediatric asthma. J Allergy Clin Immunol. 2009;123:411-416. 5. Szefler SJ et al; for the Asthma Clinical Research Network of the National Heart, Lung, and Blood Institute. Significant variability in response to inhaled corticosteroids for persistent asthma. J Allergy Clin Immunol. 2002;109:410-418. 6. Smith AD , et al. Exhaled nitric oxide: a predictor of steroid response. Am J Respir Crit Care Med. 2005;172:453-459. 7. Persson MG et al. Single-breath nitric oxide measurements in asthmatic patients and smokers. Lancet. 1994;343(8890):146-147.