FeNO Testing – What Is It and What Should I Expect?

FeNO (Fractional exhaled Nitric Oxide) testing is a quick, simple and non-invasive test that measures the level of nitric oxide in your breath. Nitric oxide is produced naturally in the lungs, and raised levels can indicate inflammation in the airways, which is commonly seen in asthma.

The test is used alongside your symptoms, medical history and other investigations, such as spirometry, to help support the diagnosis of asthma and to monitor how well inhaled steroid treatment is controlling airway inflammation. It can also help your healthcare professional decide whether inhaled steroid treatment is likely to be beneficial.

During the test, you will be asked to take a deep breath in and then breathe out slowly and steadily into the FeNO analyser for around 10 seconds. The test is painless, does not involve needles or radiation, and is suitable for most adults.

The appointment usually takes around 15–20 minutes, including an explanation of the procedure and preparation for the test. The test itself only takes a few minutes, and your result is available immediately.

To ensure the most accurate result, you may be asked to avoid eating, drinking, smoking, vaping or strenuous exercise for a short period before your appointment. Full preparation instructions will be provided when your appointment is booked.

FeNO testing provides valuable information about inflammation within your airways, but it does not diagnose asthma on its own. The results are always interpreted alongside your symptoms, clinical assessment and, where appropriate, other lung function tests.

My aim is to make the test as relaxed and straightforward as possible while providing accurate, high-quality results that can help support your diagnosis and ongoing respiratory care.