Poor Relationship Between Fractionated Exhaled Nitric Oxide and Disease Activity in Eosinophilic Esophagitis

Current eosinophilic esophagitis care requires monitoring with repeat endoscopy and biopsy, which has significant cost, risk, and inconvenience for patients. Fractionated exhaled nitric oxide testing (FeNO) is a standardized non-invasive test with proven utility in evaluation of asthma. Elevated FeNO has reported use in other eosinophilic inflammatory conditions; however, its use in eosinophilic esophagitis has not been fully evaluated. To assess the utility of FeNO in predicting severity of eosinophilic esophagitis activity. Fifty patients received fractionated exhaled nitric oxide testing within 1 week of endoscopic evaluation with biopsy for determination of peak eosinophil counts. Presence of furrows was also evaluated with respect to FeNO levels. Spearman correlation was calculated between FeNO and peak eosinophil counts (PEC) with subgroup analysis performed based on PPI use. Spearman correlation was performed on the change in FeNO and PEC on the patients receiving repeat testing. FeNO was poorly correlated to PEC (Spearman correlation 0.22). With a cut-off FeNO value of > 40 ppb, specificity of FeNO for detecting presence of ≥ 15 eos/hpf was 0.94 and sensitivity was 0.16. FeNO showed weak relationship to presence of furrows. Within the subgroup of patients not taking PPI, the spearman correlation was 0.21. Delta- FeNO versus Delta-PEC had spearman correlation of 0.72 for patients receiving repeat testing. FeNO likely has limited clinical utility for predicting severity of esophageal eosinophilia. In patients with FeNO levels > 40 ppb, specificity of testing was high, but very few patients reached this FeNO level.