Fractional Exhaled Nitric Oxide (FENO) is a simple, non-invasive test used in respiratory health. This measurement provides insights into a specific type of airway inflammation, helping healthcare providers assess lung conditions.
Understanding FENO and Its Connection to Asthma
Nitric oxide is a gas naturally produced throughout the human body, playing a role in various bodily processes. In the respiratory system, airway cells involved in inflammation produce nitric oxide. When inflamed, as in asthma, nitric oxide production increases significantly.
Elevated FENO levels in exhaled breath link specifically to eosinophilic inflammation. This inflammation involves an increase in eosinophils, a type of white blood cell, in the airway lining. Eosinophilic inflammation is a common characteristic of asthma, contributing to airway narrowing and increased sensitivity.
This inflammation leads to symptoms like wheezing, coughing, chest tightness, and shortness of breath. It also contributes to airway hyperresponsiveness, making airways overly sensitive to triggers like allergens, cold air, or irritants. By measuring FENO, providers assess the presence and severity of this underlying eosinophilic inflammation in the airways, a hallmark of many asthma cases.
How the FENO Test is Performed
The FENO test typically takes only a few minutes. Patients take a deep breath and exhale slowly and steadily into a handheld device. The device’s monitor guides them to maintain a consistent flow rate during exhalation, ensuring an accurate measurement of nitric oxide levels from the lungs.
During the test, visual feedback on the device, such as a line or target, helps patients maintain the correct exhalation pressure. This guided breathing ensures the air sampled represents nitric oxide levels in the lower airways. The process is non-invasive and generally well-tolerated.
Preparations may be suggested before the test to ensure accurate results. Patients are advised to avoid eating, drinking (other than water), smoking, or strenuous exercise for at least an hour prior. These precautions prevent factors that could temporarily alter breath nitric oxide levels, ensuring the measurement reflects the airway’s inflammatory state.
Using FENO Results for Asthma Management
FENO test results are categorized into general ranges: low, intermediate, or high, though specific cut-off values can vary. A low FENO level (typically below 25 parts per billion (ppb) for adults or 20 ppb for children) suggests eosinophilic inflammation is unlikely. Intermediate levels (often between 25-50 ppb for adults or 20-35 ppb for children) indicate a possible presence of this inflammation.
High FENO levels (usually above 50 ppb for adults or 35 ppb for children) suggest significant eosinophilic airway inflammation. These results help doctors make informed decisions for asthma diagnosis when combined with other clinical information and lung function tests. FENO is not a standalone diagnostic tool but rather a piece of the larger puzzle in assessing respiratory health.
Results also assist in monitoring the effectiveness of asthma treatments, particularly inhaled corticosteroids, which reduce airway inflammation. A decrease in FENO levels after starting or adjusting corticosteroid therapy indicates the medication effectively controls inflammation. Conversely, persistently high FENO levels suggest the current treatment regimen needs adjustment or that the patient is not adhering to medication.