From the Guidelines
Fraction of Exhaled Nitric Oxide (FeNO) is indicated for supporting a diagnosis of asthma, but it should not be used as a definitive diagnostic tool. FeNO is a non-invasive biomarker test that measures the level of nitric oxide in a patient's breath, which correlates with eosinophilic airway inflammation, a key feature of allergic/type 2 asthma 1. This test can provide supportive evidence for an asthma diagnosis, especially in patients with variable cough, wheeze, and shortness of breath 1. However, it is essential to note that FeNO has limitations as a diagnostic tool, as airway inflammation in asthma is heterogeneous and not always associated with increased FeNO 1.
Some key points to consider when using FeNO for asthma diagnosis include:
- FeNO values above 25 parts per billion (ppb) may indicate eosinophilic airway inflammation 1
- FeNO can help identify steroid responsiveness, rather than providing a definitive diagnosis 1
- The test may be falsely negative in patients who have already been treated with inhaled steroids 1
- FeNO measurement can be useful in differentiating asthma from other respiratory conditions with similar symptoms 1
According to the most recent and highest quality study 1, FeNO50 values may be elevated in healthy subjects and may be normal in subjects with asthma, highlighting the complexity of using FeNO as a diagnostic tool. However, elevated FeNO50 values can help identify T-helper 2 cell-type inflammation, a trait commonly seen in patients with asthma 1. Therefore, FeNO testing should be considered as part of a comprehensive asthma assessment, especially in cases of difficult-to-control asthma or when treatment response is suboptimal.
From the Research
Fraction of Exhaled Nitric Oxide (FeNO) in Asthma Diagnosis
- FeNO is a marker of airway inflammation and has been studied as a potential tool for asthma diagnosis and management 2, 3, 4, 5, 6
- Elevated FeNO levels are associated with asthma and reflect eosinophilic airway inflammation 2
- FeNO measurement has been proposed as a non-invasive measure of airway inflammation in asthma 5
Diagnostic Accuracy of FeNO
- The diagnostic accuracy of FeNO for asthma diagnosis has been investigated in several studies, with pooled sensitivity, specificity, and diagnostic odds ratio (DOR) of 72%, 78%, and 15.92, respectively 5
- FeNO is accurate for the diagnosis of asthma in steroid-naive or non-smoking patients, particularly in chronic cough patients 5
- The area under the summary receiver operating characteristic (sROC) curves revealed a receiver-operating characteristic of 0.88, indicating good diagnostic accuracy 5
Associations with Asthma Burden
- Higher FeNO levels are associated with greater asthma burden, including increased short-acting beta-agonist use and oral corticosteroid courses 3, 6
- FeNO levels are associated with short-acting beta-agonist use, but only among children who are not on inhaled corticosteroids 6
- FeNO measurement may be a complementary tool to help clinicians assess asthma burden and guide treatment decisions 3, 4