What is a fractional expired nitric oxide (FeNO) test and what are its implications?
- FeNO testing is a non-invasive, simple and effective test to quantify eosinophilic airway inflammation through the bio-marker nitric oxide.
- The test only requires five minutes to complete and can be used in conjunction with spirometry to indicate whether a patient has asthma.
- The American Thoracic Society in 2011, recommend the use of FeNO measurements to determine the efficacy of cortico-steroid treatment in chronic cases.
- This may come in helpful for patients with severe eosinophilic asthma whom are on a high dose of cortico-steroid and/or long-active β2-agonist to determine adequate control as;
- Recent evidence presented by Donna Carstens & colleagues in 2022, Long-term real-world effectiveness of benralizumab in patients with severe eosinophilic asthma: Results from the Zephyr 2 study, showed a reduction in asthma exacerbations for patients with uncontrolled severe eosinophilic asthma on benralizumab over a 24 month period.
- Further research is assessing the effect on eosinophil count with this medication as revealed by Eduardo Genofre and colleagues Effects of benralizumab on airway dynamics in severe eosinophilic asthma using functional respiratory imaging parameters: the buran study design.
- This may come in helpful for patients with severe eosinophilic asthma whom are on a high dose of cortico-steroid and/or long-active β2-agonist to determine adequate control as;
Clinically interpreting FeNO results:
| Adults (>18yrs) | Children (<18yrs) | Indication | Clinically sig. change | |
| Low FeNO | < 25ppb | < 20ppb | Airway inflammation unlikely | ↑ or ↓ of >10ppb |
| Intermediate FeNO | ≥ 25ppb to ≤ 50ppb | ≥ 20ppb to ≤ 35ppb | Interpret with clinical context | |
| High FeNO | >.50ppb | >.35ppb | Airway inflammation likely | ↑ or ↓ of >20% |
Interpreted from “An official ATS Clinical Practice Guideline…”, (ATS 2011).
Other uses of FeNO Testing:
- To help determine upper vs lower airway inflammation (or a combination of both) in conjunction with additional respiratory testing.
- To asses whether airway inflammation is contributing to poor asthma control.
- To better support asthma diagnosis.
- A snapshot in time of current eosinophil inflammation which can be used to determine treatment course and response for your patients.
Reference links:
DOI: 10.1164/rccm.912011ST
DOI: https://doi.org/10.1016/j.chest.2022.08.009
DOI: https://doi.org/10.1016/j.chest.2022.08.009
