Association of FeNO Decline Rate with Symptom Improvement in COPD: A Real-World Observational Study

The association between relative changes in fractional exhaled nitric oxide (FeNO) in chronic obstructive pulmonary disease (COPD) with patient-reported symptoms improvements remains uncertain.

To assess the association of the rate of FeNO decline with the achievement of the minimum clinically important difference (MCID) in COPD Assessment Test (CAT) score.

We conducted a single-center, retrospective real-world study involving 111 adults with COPD. Patients were classified into two groups: those with symptom improvement (CAT decline ≥2 points) and those with no improvement (CAT decline <2 points). Logistic regression evaluated associations between FeNO decline rate and CAT MCID, adjusting for clinically relevant covariates. Receiver operating characteristic (ROC) curve analysis estimated the discriminatory performances of it.

Of 111 patients, 53 (47.7%) achieved the CAT MCID. Multivariate logistic regression found that the rate of FeNO decline was independently associated with symptom improvement (adjusted OR 2.08, 95% CI 1.01-4.29, P=0.047). Baseline CAT also showed association with symptom improvement (adjusted OR 1.06, 95% CI 1.00-1.12, P=0.034). BMI showed a positive trend but without statistical significance (adjusted OR 1.13, 95% CI 1.00-1.29, P=0.056). AUC of FeNO decline rate, baseline CAT, combined with BMI in discriminating CAT MCID were 0.713 (95% CI 0.617, 0.809).

The rate of FeNO decline was significantly associated with clinically meaningful CAT improvement in this study, which indicated dynamic measures of type-2 inflammation can complement blood eosinophil counts to refine phenotyping and inform precision management in COPD.