Role of fractional exhaled nitric oxide(FeNO) in obstructive airway diseases in Indian population

Abstract

Introduction: The diagnosis of Asthma is usually based on signs-symptoms,PFT and bronchial challenge test but none reflect ongoing airway inflammation.Hence direct measurement of airway inflammation by measuring FeNO may be more appropriate for diagnosis. Aims/Objectives: To estimate the range of FeNO in patients of obstructive airway diseases(OAD) in Indian population. To assess the correlation between FeNO and standard spirometry. To determine the cut off values of FeNO for diagnosing Asthma. Methods: A prospective study comparing FeNO to spirometry was done in 175 patients suspected of having OAD presenting to OPD. FeNO was measured with an electrochemical analyzer(NObreath FeNO monitor)followed by spirometry. Results: The mean FeNO values are higher in asthmatics as compared to COPD patients with statistically significant (p value 0.04) difference. The range of FeNO values in the Asthma and COPD groups is between 5-300 ppb and 10-47 ppb respectively. The cut off value of FeNO for diagnosing asthma with maximum sensitivity and specificity is 24.5 ppb. The correlation of FeNO with Spirometry is as follows: FeNO is more sensitive tool in diagnosing Asthma than Standard Spirometry. The concordance rate between FeNO and Spirometry is very poor,so both test should be interpreted separately in diagnosing Asthma. FeNO does not correlate with severity of obstruction as shown by spirometry so it shouldn9t be used to assess the severity of OAD independently. Conclusion: Above findings suggest that there are higher chances of missing Asthma if we strictly apply spirometric criteria only. FeNO measurements may aid in increased diagnostic yield and differentiating between asthma and COPD.