Within-day variability of Fractional exhaled Nitric Oxide in stable COPD patients.

<bold>Introduction:</bold> There is renewed interest in Fractional exhaled Nitric Oxide (F_ENO₅₀) as biomarker of type 2 inflammation in COPD. In addition, F_ENO₅₀ might also predict the risk and etiology of exacerbations. Within-day variability of F_ENO₅₀ needs to be established for it to become a usable biomarker in COPD. <bold>Aim and objectives:</bold> To prospectively determine the within-day variability of F_ENO₅₀ in stable COPD patients. <bold>Methods:</bold> Spirometry confirmed COPD patients were recruited at the outpatient clinic of a tertiary hospital and a primary care practice. Excluded were patients with asthma, smoking history of <10 packyears, active malignancy, use of systemic corticosteroids <6 weeks or an exacerbation <4 weeks. In each patient, F_ENO₅₀ was determined (according to ATS/ERS recommendation) at 8h, 12h and 16h. <bold>Results:</bold> Sixty-nine patients were included (mean age 68 ±7(SD) years, 61% male, 48% current smokers, 41% on Inhaled Corticosteroids (ICS)). There were no significant F_ENO₅₀ differences between measurement time points (p>0.1). Median [IQR] F_ENO₅₀ levels at 8h, 12h and 16h were 18 [12-28], 18 [11-28] and 16 [12-28] ppb (Figure 1) with a within-day CoV of 14% [8-22%] and an intra-class correlation coefficient of 0.92 (CI:0.88-0.94) which was not affected by ICS use. <fig><object-id>erj;64/suppl_68/PA3975/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Conclusion:</bold> In a cohort of stable COPD patients the within-day variability of F_ENO₅₀ was low, suggesting that time of day does not need consideration when using it as a biomarker.