Evaluation of exhaled nitric oxide's ability to predict methacholine challenge in adults with nonobstructive spirometry.

Background: Compared with methacholine challenge, exhaled nitric oxide is less expensive, is performed as a simpler point-of-care maneuver, and may provide treatment guiding information.

Objective: To determine whether exhaled nitric oxide levels can predict the outcome of methacholine challenge in patients without obvious baseline obstruction.

Methods: This retrospective database and medical record review included adults presenting to a tertiary care center from November 1, 2009, through August 31, 2013, who underwent methacholine challenge and exhaled nitric oxide measurement within 2 weeks of each other. Database extraction identified age, sex, body mass index, baseline corticosteroid use, testing indication, forced expiratory volume in 1 second (FEV), and testing results. Individuals taking corticosteroid-containing medication or who had an FEV less than the lower limit of normal at baseline were excluded.

Results: A total of 1,322 individuals were identified, with 774 meeting the eligibility criteria. A total of 123 methacholine challenges (16%) had positive results. Fractional exhaled nitric oxide was statistically higher in those with positive methacholine challenge results (mean [SD], 41.9 [54.5] ppb vs 25.2 [19.7] ppb; P < .01). Receiver operating characteristic curve revealed an area under the curve of 0.572 (P < .01), suggesting a poor correlation between exhaled nitric oxide level and methacholine challenge outcome. Fractional exhaled nitric oxide of greater than 50 ppb has a sensitivity, specificity, positive predictive value, and negative predictive value of 12%, 89%, 17%, and 84%, respectively, for a positive methacholine challenge result.

Conclusion: In this large, retrospective cohort of corticosteroid-naive pulmonary patients with normal FEV on baseline spirometry, exhaled nitric oxide poorly predicts the outcome of a methacholine challenge.