From the Guidelines
Rhinitis and nasal polyps generally do not lower fractional exhaled nitric oxide (FeNO) levels; in fact, they often increase them. Allergic rhinitis typically causes elevated FeNO levels due to the type 2 inflammation that occurs in both the upper and lower airways [ 1 ]. Similarly, nasal polyps, especially those associated with eosinophilic inflammation, are frequently linked to increased rather than decreased FeNO measurements. This relationship exists because the same inflammatory pathways that drive these upper airway conditions often affect the lower airways as well.
Key Points to Consider
- The presence of rhinitis and nasal polyps can impact FeNO levels, but the effect is typically an increase rather than a decrease [ 1 ].
- Proper FeNO measurement technique is crucial, as mouth breathing through the nose during the test can contaminate the sample with nasal nitric oxide, which is naturally higher than bronchial nitric oxide.
- When interpreting FeNO results in patients with rhinitis or nasal polyps, clinicians should consider the potential influence of upper airway inflammation and ensure proper testing technique with complete nasal occlusion during the measurement to obtain accurate readings that reflect lower airway inflammation [ 1 ].
Clinical Implications
- Clinicians should be aware that rhinitis and nasal polyps can increase FeNO levels, and this should be taken into account when interpreting FeNO results in patients with these conditions [ 1 ].
- The management of chronic rhinosinusitis with nasal polyposis (CRSwNP) is important, as it can negatively impact quality of life, and optimal patient outcomes require systematic summaries of all available evidence [ 1 ].
From the Research
Fractional Exhaled Nitric Oxide (FENO) Levels in Rhinitis and Nasal Polyps
- The relationship between rhinitis, nasal polyps, and FENO levels is complex, with some studies suggesting that FENO levels may be decreased in patients with chronic rhinosinusitis and nasal polyps 2, 3.
- A study published in 2019 found that FENO levels were significantly lower in patients with nasal inflammation than in healthy subjects, and that FENO had a high sensitivity and specificity for diagnosing chronic rhinosinusitis 2.
- Another study published in 2015 found that nasal NO (nNO) levels were lower in patients with chronic rhinosinusitis and nasal polyps, while fractional exhaled nitric oxide (FENO) levels were higher 3.
- The evidence suggests that FENO levels may be affected by the presence of rhinitis and nasal polyps, but the exact relationship is not fully understood and may depend on various factors, including the severity of the disease and the presence of other conditions 4, 5.
Factors Influencing FENO Levels
- The severity of chronic rhinosinusitis and nasal polyps may influence FENO levels, with more severe disease associated with lower nNO levels and higher FENO levels 3.
- The presence of eosinophilic inflammation in the nasal mucosa may also affect FENO levels, with higher FENO levels observed in patients with eosinophilic chronic rhinosinusitis 5.
- Treatment with corticosteroids, such as fluticasone propionate nasal drops, may reduce the need for surgery in patients with nasal polyposis and chronic rhinosinusitis, but its effect on FENO levels is not clear 6.
Measurement of FENO Levels
- FENO levels can be measured using an electrochemical NO analyzer or a fractional exhaled nitric oxide detector 4, 2.
- The measurement of FENO levels may be useful for monitoring the extent of inflammation in patients with chronic rhinosinusitis and nasal polyps, and for evaluating the response to treatment 4, 5.