FeNO (Fractional exhaled Nitric Oxide) is a non-invasive test used to measure the level of nitric oxide gas in a person's exhaled breath. It is a useful tool in assessing airway inflammation, particularly in patients with asthma.
Indications for FeNO testing:
1. Asthma diagnosis and monitoring: FeNO levels can help in diagnosing asthma, especially in cases where traditional spirometry results are inconclusive. It can also aid in monitoring asthma control and adjusting treatment accordingly.
2. Assessing eosinophilic airway inflammation: FeNO is a marker of eosinophilic airway inflammation, which is common in certain types of asthma and other respiratory conditions.
3. Differentiating between eosinophilic and non-eosinophilic asthma: FeNO can help distinguish between different asthma phenotypes and guide personalized treatment approaches.
4. Evaluating steroid responsiveness: FeNO levels may predict a patient's response to corticosteroid therapy, aiding in treatment decisions.
Prerequisites for FeNO testing:
1. Avoiding certain substances: The patient should avoid smoking, alcohol, caffeine, and certain foods (e.g., beetroot, spinach) at least one hour before the test, as they may affect FeNO levels.
2. Compliance with medication: If the patient is on asthma medications, they should continue taking their prescribed medications as directed by their healthcare provider.
3. No respiratory infections: FeNO testing should not be performed during an acute respiratory infection or within two weeks of a respiratory illness.
Interpretation of FeNO results:
FeNO levels are typically reported in parts per billion (ppb). The interpretation of FeNO results can vary depending on the clinical context and the patient's specific condition. Generally, the following guidelines can be used:
1. Normal FeNO levels: In adults, FeNO levels below 25 ppb are considered normal. For children, the cutoff may be lower, typically around 20 ppb.
2. Elevated FeNO levels: FeNO levels above the normal range indicate airway inflammation, often associated with conditions such as asthma or allergies. Elevated FeNO levels can suggest eosinophilic inflammation, which may respond well to corticosteroid treatment.
3. Low FeNO levels: FeNO levels below the normal range may indicate non-eosinophilic inflammation or other types of asthma that may not respond as effectively to corticosteroids.
It is essential to note that FeNO results should be interpreted alongside other clinical information, such as the patient's medical history, symptoms, physical examination, and other diagnostic tests like spirometry. FeNO testing is a valuable tool, but it is not a standalone diagnostic test and should be used as part of a comprehensive assessment of respiratory health. Interpretation of FeNO results should be done by a qualified healthcare professional, such as an allergist, pulmonologist, or respiratory therapist.