From the Guidelines
Patients with suspected asthma should not use inhaled corticosteroids (ICS) for at least 4 weeks before FeNO testing to ensure accurate results. This is based on the understanding that ICS directly reduce airway inflammation, which is what FeNO measures, and using them before the test could lead to falsely low readings 1.
Pre-Test Preparation
To prepare for FeNO testing, the following guidelines are recommended:
- Short-acting beta-agonists (SABAs) like albuterol/salbutamol can be used as needed for symptom relief during this period but should be avoided for 6-8 hours before the test.
- Antihistamines and leukotriene modifiers (like montelukast) should also be discontinued 72 hours before testing.
- Patients should avoid strenuous exercise, alcohol, caffeine, and smoking for at least 1 hour before the test.
- Nitrate-rich foods (like leafy greens) should be avoided for 3 hours before testing, as they can temporarily alter nitric oxide levels in the airways.
Rationale
These precautions are necessary because FeNO measures airway inflammation, and certain medications and activities can temporarily alter nitric oxide levels in the airways, potentially affecting the test results 1.
Monitoring and Emergency Care
Patients should continue to monitor their symptoms during this preparation period and seek emergency care if they experience severe respiratory distress. The interpretation of FeNO results should be done in conjunction with symptoms, history, physical exam, and lung function assessment, as outlined in the clinical practice guideline 1.
From the FDA Drug Label
The use of albuterol sulfate inhalation solution can be continued as medically indicated to control recurring bouts of bronchospasm The FDA drug label does not answer the question.
From the Research
Treatment of Suspected Asthma Patients Before FeNO Testing
- The treatment of suspected asthma patients before FeNO testing is crucial in determining the accuracy of the test results 2.
- According to the Global Initiative of Asthma Guideline, a flowchart is recommended to diagnose asthma, which includes spirometry with reversibility and a bronchial challenge test (BPT) with histamine or methacholine as a second step 2.
- However, the BPT is considered burdensome, time-consuming, and expensive, and can cause side effects, which is why the FeNO-test is being considered as an 'add-on' test in asthma diagnostics 2.
- Studies have shown that inhaled corticosteroids (ICSs) and long-acting inhaled beta(2)-agonists (LABAs) are effective in treating asthma, and that fixed-dose combinations of ICSs and LABAs can improve lung function and symptom control 3, 4, 5.
- Before FeNO testing, patients with suspected asthma may be treated with short-acting beta 2-agonists and oral corticosteroids to control their symptoms, and their response to these treatments can be used as markers of asthma control 3.
- The FeNO-test can be used to rule in a diagnosis of asthma with confidence, but due to its poor sensitivity, it is not suitable to rule out asthma 2.
- Specific cutoff levels for FeNO levels can predict the positive methacholine challenge, with significant confounding factors being atopy and current smoking 6.
Factors to Consider Before FeNO Testing
- Atopy and current smoking can affect FeNO levels and should be considered when interpreting test results 6.
- The use of ICSs and LABAs can also affect FeNO levels, and patients should be instructed to withhold these medications for a certain period before FeNO testing 4, 5.
- The FeNO-test is a low-burden test that can be used to measure airway eosinophilic inflammation in asthma patients, and its results can be used to guide treatment decisions 2.