Fractional exhaled nitric oxide (FENO)

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FeNO is a biomarker of airway inflammation and is commonly associated with asthma. The test is simple and quick to perform and only requires gentle breathing. FeNO is a valuable tool to assist in a diagnosis of asthma. The data obtained also provides meaningful information which allows your doctor to prescribe the right amount of inhalers that you should be taking to control asthma symptoms and prevent exacerbations.

In medicine, exhaled nitric oxide (eNO) can be measured in a breath test for asthma or other conditions characterized by airway inflammation. Nitric oxide (NO) is a gaseous molecule produced by certain cell types in an inflammatory response. The fraction of exhaled NO (FENO) is a promising biomarker for the diagnosis, follow-up and as a guide to therapy in adults and children with asthma. The breath test has recently become available in many well-equipped hospitals in developed countries, although its exact role remains unclear.

During inflammation, higher-than-normal levels of nitric oxide (NO) are released from epithelial cells of the bronchial wall. The concentration of NO in exhaled breath, or fractional exhaled nitric oxide (FeNO), can help identify airway inflammation, and thereby support a diagnosis of asthma when other objective evidence is lacking.

Patients with asthma have higher eNO levels than other people. Their levels also rise together with other clinical and laboratory parameters of asthma (for example, the amount of eosinophils in their sputum). In conditions that trigger inflammation such as upper respiratory tract infections or the inhalation of allergens or plicatic acid, eNO levels rise. The eNO levels also tend to vary according to the results of lung function test results such as the degree of bronchial hyperresponsiveness. Furthermore, drugs used to treat asthma (such as inhaled glucocorticoids or leukotriene receptor antagonists) also reduce eNO levels.

Clinical trials have looked at whether tailoring asthma therapy based on eNO values is better than conventional care, in which therapy is gauged by symptoms and the results of lung function tests.To date, the results in both adults and children have been modest and this technique can not be universally recommended. It has also been noted that factors other than inflammation can increase eNO levels, for example airway acidity.

The fraction of eNO has been found to be a better test to identify asthmatics than basic lung function testing (for airway obstruction). Its specificity is comparable to bronchial challenge testing, although less sensitive. This means that a positive eNO test might be useful to rule in a diagnosis of asthma; however, a negative test might not be as useful to rule it out.

The role for eNO in other conditions is even less well established compared to asthma.

Relevant Specialties
Respiratory and Sleep Medicine
Medical Conditions

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