Johnson K, et al. - The utility of fractionated exhaled nitric oxide testing (FeNO) in predicting the severity of eosinophilic esophagitis activity was evaluated. In this analysis, 50 subjects received fractionated exhaled nitric oxide testing within 1 week of endoscopic evaluation with biopsy for determination of peak eosinophil counts. For predicting the severity of esophageal eosinophilia, FeNO likely had limited clinical utility. Researchers found that specificity of testing was high in patients with FeNO levels > 40 ppb. It was noted that very few patients reached this FeNO level.