Cutoff point for exhaled nitric oxide corresponding to 3% sputum eosinophils

Area of Science:

• Pulmonology
• Allergy and Immunology
• Biomarkers

Background:

• Eosinophilic asthma phenotype (≥3% sputum eosinophils) predicts positive response to corticosteroids and T(H)2 immunomodulators.
• Exhaled nitric oxide (FeNO) is a non-invasive marker correlated with eosinophilic airway inflammation.
• Portable FeNO devices offer rapid assessment of potential eosinophilic asthma.

Purpose of the Study:

• To determine the optimal FeNO threshold that best correlates with 3% sputum eosinophilia in asthma patients.
• To evaluate the diagnostic performance of FeNO in identifying airway eosinophilia.

Main Methods:

• 129 non-smoking asthma patients underwent skin tests, FeNO measurement, spirometry, induced sputum analysis, and Asthma Control Test.
• Receiver operating characteristic (ROC) curves and logistic regression were employed for analysis.

Main Results:

• A FeNO cutoff of 21 ppb demonstrated the best fit for identifying ≥3% sputum eosinophilia.
• This cutoff showed higher sensitivity (97%) and negative predictive value (88%) in corticosteroid-naïve patients.
• FeNO performance was reduced in patients already receiving corticosteroids.

Conclusions:

• FeNO levels ≥ 21 ppb are indicative of airway eosinophilia in asthma.
• In corticosteroid-naïve individuals, FeNO < 21 ppb can reliably exclude airway eosinophilia.