Little is known about Fractional concentration of exhaled Nitric Oxide (FeNO) as a predictor of mortality in persons with asthma or chronic obstructive pulmonary disease (COPD).

This study tested the hypotheses that FeNO level ≥ 25 ppb was associated with mortality in a national cohort of persons with asthma or COPD age ≥ 40 years.

In the 2007–2012 National Health and Nutrition Examination Survey (NHANES), FeNO was measured using an electrochemical sensor. Mortality was determined through 2015 using linkage to the National Death Index. Weighted Cox proportional hazards survival analysis was performed taking the complex survey design into account using STATA V.17.

Among the 611 participants with current asthma, 5.16% died during the follow-up period. FeNO ≥ 25 ppb was associated with a hazard ratio (HR) of 0.20, (p = 0.006, 95% CI:0.068–0.618) alone or with little change after controlling for confounding variables. Due to effect modification, the analysis was repeated in persons with and without a history of emergency department (ED) visit for asthma in the previous year. In 522 persons without ED visits, FeNO ≥ 25 ppb was significantly associated with mortality HR 0.094, 95 CI 0.034–0.26, p < 0.001. In 83 persons with ED visits no significant association remained after controlling for all confounders. (Six persons were omitted from this analysis due to missing data on confounders in the extended regression model.) Among 614 with COPD, FeNO ≥ 25 ppb was not associated with mortality.

In persons with current asthma at baseline, FeNO ≥ 25 ppb was associated with reduced hazard of mortality during follow up among those with no history of ED visits in the previous year. No significant association of FeNO with mortality was seen in persons with COPD.