Fractional Exhaled Nitric Oxide (FeNO) Testing for Respiratory Assessment in a 59-Year-Old Male
For a 59-year-old male, fractional exhaled nitric oxide (FeNO) measurement should be used as a diagnostic and monitoring tool for eosinophilic airway inflammation and asthma, with interpretation based on specific cut-points: values <25 ppb indicate low likelihood of eosinophilic inflammation, 25-50 ppb require cautious interpretation with clinical context, and >50 ppb indicate high likelihood of eosinophilic inflammation and steroid responsiveness. 1
Understanding FeNO in Adult Males
FeNO is a biomarker that measures exhaled nitric oxide, which reflects eosinophilic airway inflammation and helps guide corticosteroid therapy decisions. 1 The American Thoracic Society strongly recommends its use for diagnosing eosinophilic airway inflammation and determining steroid responsiveness in patients with chronic respiratory symptoms. 1
Normal Reference Values for 59-Year-Old Males
For a 59-year-old male, the expected upper limit of normal FeNO varies by height and atopy status: 1
Non-atopic males aged 50-75 years:
- Height 160-169 cm: 35 ppb
- Height 170-179 cm: 39 ppb
- Height 180-189 cm: 44 ppb
- Height 190-199 cm: 49 ppb
Atopic males aged 50-75 years:
- Height 160-169 cm: 63 ppb
- Height 170-179 cm: 62 ppb
- Height 180-189 cm: 57 ppb
Clinical Interpretation Algorithm
Low FeNO (<25 ppb)
In symptomatic patients with FeNO <25 ppb, eosinophilic airway inflammation is unlikely and the patient will probably not benefit from inhaled corticosteroid treatment. 1 Consider alternative diagnoses including: 1
- Non-eosinophilic asthma (steroid unresponsive)
- Vocal cord dysfunction
- Cardiac disease
- Bronchiectasis
- Gastroesophageal reflux disease
- Rhinosinusitis
In asymptomatic patients with established asthma and low FeNO, this implies adequate anti-inflammatory therapy dosing and good adherence. 1 Inhaled corticosteroid dose may be reduced, with repeat FeNO measurement 4 weeks later to confirm stability. 1
Intermediate FeNO (25-50 ppb)
Values between 25-50 ppb require cautious interpretation with close attention to clinical context and serial monitoring. 1 The American Thoracic Society recommends monitoring changes in FeNO over time rather than making immediate treatment decisions based on a single intermediate value. 1
High FeNO (>50 ppb)
FeNO >50 ppb indicates eosinophilic airway inflammation is present and the patient is likely to benefit from inhaled corticosteroid treatment. 1
In symptomatic patients presenting for the first time with FeNO >50 ppb, possible diagnoses include: 1
- Atopic asthma
- Eosinophilic bronchitis
- COPD with mixed inflammatory phenotype
In patients with established asthma and persistently elevated FeNO >50 ppb despite treatment, consider: 1
- Poor medication adherence
- Incorrect inhaler technique
- High persistent allergen exposure
- Inadequate inhaled corticosteroid dose
- Proximal drug deposition with untreated distal airway inflammation
Monitoring Airway Inflammation
The American Thoracic Society strongly recommends using FeNO to monitor airway inflammation in patients with asthma, though the quality of evidence is low. 1 The change in FeNO following corticosteroid intervention may be more clinically valid than absolute values. 1
Clinically Significant Changes
A significant increase in FeNO is defined as: 1
20% increase for baseline values >50 ppb, OR
10 ppb absolute increase for baseline values <50 ppb
A significant response to anti-inflammatory therapy is indicated by: 1
- ≥20% reduction for baseline values >50 ppb, OR
- ≥10 ppb absolute reduction for baseline values <50 ppb
Important Clinical Caveats
FeNO interpretation must always be used as an adjunct to history, physical examination, and lung function assessment—never in isolation. 1
Account for persistent or high allergen exposure, which is associated with higher FeNO levels independent of disease control. 1
In asymptomatic patients with high FeNO, some may have no active disease as "high" FeNO may be normal in a certain percentage of the population, but elevated values could indicate risk for upcoming exacerbation. 1
Note that inhaled nitric oxide gas therapy (iNO) is an entirely different intervention from FeNO testing—iNO is FDA-approved only for hypoxic respiratory failure in neonates and has limited adult indications such as pulmonary hypertension or as a bridge to thrombolysis in severe pulmonary embolism with hypoxemia. 2, 3