Fractional exhaled nitric oxide (FeNO) test

Nitric oxide is a gas produced naturally in the airways, primarily by the cells that line the bronchi. Its concentration in exhaled air can increase if there is bronchial inflammation, especially when there is eosinophilic inflammation (accumulation of eosinophils, a type of white blood cell), with or without allergies; this is characteristic of asthma. 

The test can: 

• Detect airway inflammation. 

• Confirm the diagnosis of bronchial asthma and be used to monitor these patients. 

• Help in the phenotyping of patients with asthma, especially those with severe asthma.  

• Evaluate the response and adherence to anti-inflammatory treatment, especially with inhaled corticosteroids. 

• Identify patients at higher risk of asthma exacerbations or attacks. 

This is a very simple, quick and safe technique. The patient blows slowly through a mouthpiece connected to a device that measures the nitric oxide concentration in the exhaled air. 

The procedure is guided at all times by a healthcare professional, who provides clear instructions to ensure accurate measurement. 

The test does not require any special preparation. The patient should not smoke before taking the test and should inform healthcare personnel about their use of any inhaled treatments; although these are generally not discontinued, unless directed by their medical team.  

FeNO measurement is performed by trained healthcare personnel: nurses, technicians or physiotherapists with specific training in pulmonary function techniques. 

The test results are evaluated by a pulmonologist, who includes them with the rest of the clinical evaluation results to establish a diagnosis, modify treatment or monitor bronchial inflammation. 

The test is well tolerated by most patients. Some people may experience a mild cough or a mild, temporary feeling of shortness of breath when exhaling. At all times, the patient is accompanied by healthcare personnel who supervise the test and ensure patient safety and comfort.