Cleveland Clinic Journal of MedicineMeasuring Exhaled Nitric Oxide when Diagnosing and Managing Asthma

Understanding the Role of Exhaled Nitric Oxide in Asthma Diagnosis and Management

Measuring the fractional concentration of exhaled nitric oxide (FeNO) offers valuable insights in the diagnosis and management of asthma, although it should not be used as a standalone diagnostic tool. This method aids in identifying patients who may benefit from inhaled corticosteroids, monitoring treatment efficacy, predicting exacerbations, and assessing treatment adherence. The clinical application of FeNO measurements must be integrated with other diagnostic methods and clinical evaluations to ensure accuracy and effectiveness in asthma care.

Key Points:

• Role of Nitric Oxide in Asthma:
  • Nitric oxide is produced in the airways during type 2 inflammation, commonly seen in asthma.
  • The fractional concentration of exhaled nitric oxide (FeNO) serves as an adjunctive test for asthma diagnosis.
• Diagnostic Use of FeNO:
  • FeNO testing has a sensitivity of 65% and specificity of 82% for diagnosing asthma.
  • Elevated FeNO levels can complement clinical history and spirometry testing, especially when clinical suspicion is high.
  • Confounding factors (e.g., rhinosinusitis, atopy, air pollution, smoking) must be considered as they can affect FeNO levels.
• Predicting Steroid Responsiveness:
  • High FeNO levels predict a better response to inhaled corticosteroids and biologic therapy.
  • FeNO can guide the dosage adjustments of inhaled corticosteroids, both for increasing and tapering doses.
• Monitoring Treatment and Adherence:
  • FeNO measurement can help monitor the effectiveness of inhaled corticosteroids and identify nonadherence.
  • A reduction in FeNO levels after observed corticosteroid administration indicates adherence.
• Predicting Exacerbations:
  • Higher FeNO levels correlate with an increased risk of asthma exacerbations.
  • Combining FeNO measurements with peripheral blood eosinophil counts enhances the prediction accuracy for exacerbations.
• Expert Recommendations:
  • National and international guidelines recommend using FeNO as part of a comprehensive asthma management strategy.
  • FeNO should be measured in conjunction with other diagnostic tools like spirometry and clinical evaluations.
• Clinical Practice Implications:
  • FeNO testing adds value in selecting and monitoring patients for corticosteroid therapy.
  • It helps in making informed decisions about step-down therapy to avoid unnecessary high-dose corticosteroid exposure.
  • FeNO testing aids in differentiating asthma endotypes and tailoring biologic therapies accordingly.

HCN Medical Memo
FeNO testing enhances asthma care by aiding in the selection and monitoring of patients for corticosteroid therapy, enabling informed decisions on step-down therapy to avoid unnecessary high-dose exposure. It differentiates asthma endotypes and tailors biologic therapies accordingly, improving treatment outcomes and adherence.

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