Nitric Oxide Airway Measurements

18 March 2024
Nitric Oxide Airway Measurements


When are nitric oxide airway measurements useful? Is it worth me buying a machine to measure it?


Answer (2024)
By Cesar Galvan Calle
, MD (Lima, Peru)

Nitric oxide (NO) acts as an internal mediator, playing a role in various cellular and tissue functions, including the respiratory system. In this context, it regulates the tone of bronchial smooth muscles, influences neurotoxicity, modulates mucus transport, and contributes to surfactant production (1).

Fractional exhaled nitric oxide (FeNO) serves as a biomarker used to identify potential type 2 inflammation in both the upper and lower airways. It is commonly employed in asthma treatment, offering significant advantages over other tests related to inflammation, such as blood eosinophil count, due to its non-invasive nature, ease of application, and well-tolerance in both adult and pediatric patients (2).

Concerning asthma diagnosis, adults and children experiencing asthmatic symptoms with low FeNO concentrations may suggest that eosinophilic inflammation is less likely. In such cases, alternative diagnoses like non-allergic asthma, gastroesophageal reflux, or vocal cord dysfunction could be considered (2), as recommended for some years by the guidelines of the American Thoracic Society (ATS) and the European Respiratory Society (ERS) (3).

High baseline FeNO levels in severe asthma patients starting biologic therapy predict better clinical control and fewer exacerbations, highlighting its biomarker potential for biologic response (4). A meta-analysis from 2023 found that FeNO-guided asthma treatment plays a crucial role in predicting the response to treatment, although a specific protocol on cut-off points has not yet been fully established. Additionally, the treatment has the potential to reduce the number of patients experiencing at least one exacerbation by 39% and lower the frequency of exacerbations by 33% based on findings from six Randomized Controlled Trials studies (5). Another notable benefit lies in its ability to identify improper inhaler use during asthma treatment. If FeNO levels do not decrease upon initiating inhaler use, this may indicate issues as simple as incorrect technique on the part of the patient (6).

Measuring FeNO values could be valuable in patients with chronic rhinosinusitis and rhinitis, as there exists a correlation between exhaled nitric oxide levels and nasal and sinus mucosal inflammation, along with symptom severity (7). Additionally, FeNO may serve as an indicator in occupational asthma inflammation, given its correlation with methacholine hyperreactivity. Although there is no consensus on the cut-off point for diagnosis, its use is recommended 24 hours after occupational exposure (8). In patients with chronic obstructive pulmonary disease (COPD), a slight increase in FeNO levels has been observed. However, a definitive association between exacerbated COPD and FeNO levels is yet to be established (9).

A cost-effectiveness study, simulating asthma treatment based on current standards of care and comparing these standards with the addition of FeNO, revealed that incorporating FeNO into the treatment regimen could lead to a yearly reduction in patient costs by $409 and an enhancement in health-adjusted quality of life (10). Therefore, the investment in a FeNO measurement device is justified, depending on the type of patients you treat. This measurement is useful for monitoring inflammation, assisting in the diagnosis and management of asthma, as well as considering other possible diagnoses.


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Answer (2019)
By Glenis K. Scadding

Nitric oxide (NO) is produced from the amino acid arginine via the enzyme nitric oxide synthase.

It is a potent biological mediator which has a regulatory role in many cellular and tissue functions. In the upper and lower airways, NO is involved in regulatory, protective, defensive functions, but can have damaging effects. NO forms part of innate immunity, being constitutively generated at high concentrations in the paranasal sinuses.

Nitric oxide levels may reflect the inflammatory status of both the upper and lower airways. Measurement of exhaled bronchial nitric oxide is a useful, non-invasive tool in the diagnosis and management of eosinophilic asthma, since it is normally low unless nitric oxide synthase is induced by the inflammatory response. Normal levels indicate that lower airways eosinophilic inflammation is absent or controlled by therapy. NO levels may also help in the diagnosis of chronic cough.

Nasal nitric oxide is more complex since two factors are involved: high continually present sinus NO enters the nose via the ostiomeatal complex, but the nasal mucosa can also form inducible nitric oxide in an inflammatory response. Therefore nasal NO may be normal, raised or lowered in disease states. However measurement may be a useful tool in the diagnosis and management of patients with chronic rhinosinusitis, nasal polyps, and cystic fibrosis, as well as in the diagnosis of primary ciliary dyskinesia (PCD), where nasal NO is very low. In conditions where the ostiomeatal complex is blocked (such as nasal polyps) nasal NO tends to be low and to improve with nasal corticosteroids, correlating with the improvement in polyp grade. Further research is aimed at investigating the role of nitric oxide in allergic rhinitis, where results are variable, but tend to be elevated in active disease and lowered by nasal corticosteroids.

Measuring both bronchial and nasal nitric oxide may assist the combined management of upper and lower airways: for example in the coughing child normal exhaled NO (from the lower airways) suggests that the pathology is more likely to be in the upper respiratory tract.

Whether NO measurements are useful in your practice depends on the patients whom you are seeing. (FENO) values obtained using a portable analyzer correlate well with those obtained using an established laboratory analyzer and can be used to discriminate asthmatic from non-asthmatic patients. This may facilitate the measurement of asthmatic airway inflammation in primary care.

I have found NO very helpful in subjects with both upper and lower airway conditions, where they can obviate the need for a repeat CT scan, alert one to the likelihood of PCD or cystic fibrosis or to the fact that a patient is not using their inhaled corticosteroids in sufficient quantity.

There are guidelines for making the measurements accurately.



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