Exhaled Nitric Oxide Testing – FeNO
Most of us know that the air we breathe affects our lungs. What you may not know is that the air you breathe out can tell us how.
For instance: We all exhale a little nitric oxide (NO). But too much nitric oxide is an indicator of lung inflammation, the underlying condition of asthma. Measuring nitric oxide levels in your breath (FeNO, or fractional exhaled nitric oxide) can be useful in testing for and monitoring asthma. The noninvasive test involves breathing into a machine that detects FeNO levels; it is easily performed by patients of all ages.
Clinical practice guidelines from the American Thoracic Society (ATS) give physicians using FeNO testing a standardized way of interpreting results. Raed Dweik, MD, chairman of the ATS committee that developed the guidelines, says, “In patients with nonspecific respiratory symptoms, FeNO can help the clinicians determine if they have airway inflammation – a major feature in asthma – or not. In individuals with established asthma, FeNO can help determine how well-treated and controlled – or not – the inflammation is.”
Peter Boggs, MD, the only allergist who was part of the ATS guidelines-writing committee, says the guidelines help physicians tell more clearly if an asthma patient’s inhaled corticosteroid treatment is effective. Since corticosteroid treatment should reduce inflammation, if a person with asthma who’s on such an anti-inflammatory medication still shows above-threshold levels of exhaled nitric oxide, it could indicate that the drug or its dosage needs to be changed, the person isn’t using the inhaler properly, or the person isn’t keeping up with treatments. But it could also indicate that the medication therapy is being overpowered by exposure to environmental allergens and irritants like pet dander or a less obvious trigger.
Boggs stresses that FeNO testing doesn’t replace other asthma diagnostic tools. “FeNO supports the diagnosis of asthma, it does not make it,” he says. “No single test actually makes the diagnosis; it is a combination of the patient’s medical history, physical findings, pulmonary function assessment, and FeNO. Together, these yield very helpful information.”
Read more: Ask the Allergist: Measuring Inflammation