Abbreviation modalities of nitrogen multiple‐breath washout tests in school children with obstructed lung disease

Summary Rationale: Nitrogen multiple‐breath washout (N 2 MBW) is a promising tool for assessing early lung damage in children with chronic obstructive pulmonary disease, but it can be a time‐consuming procedure. We compared alternative test‐shortening endpoints with the most commonly reported N 2 MBW outcome, the lung clearance index, calculated as lung volume turnovers required to reach 2.5% of the starting N 2 concentration (LCI 2.5 ). Methods: Cross‐sectional study of triplicate N 2 MBW measurements obtained in cystic fibrosis (CF) patients (N = 60), primary ciliary dyskinesia (PCD) patients (N = 28), and matched healthy controls (N = 48) aged 5–18 years. Bland–Altman analysis was used to compare LCI 2.5 with earlier LCI endpoints (3%, 4%, 5%, 7%, and 9% of starting N 2 concentration), Cn@TO6 (defined as % of N 2 starting concentration when reaching six lung volume turnovers), and LCI derived from only two N 2 MBW runs in each session. N 2 MBW endpoints were analyzed as z‐scores calculated from healthy controls. Results: In PCD, Cn@TO6 and LCI 2.5 exhibited similar values (mean [95%CI] difference: 0.33 [−0.24; 0.90] z‐scores), reducing the test duration by one‐third (5.4 min; 95%CI: 4.0; 6.8). All other tested alternative endpoints exhibited increasing disagreement with increasing LCI 2.5 . With an average reduction in test duration of 40%, LCI 2.5 derived from two runs exhibited good agreement in all children. Conclusions: Cn@TO6 may be suggested as a potential test‐shortening endpoint in school children with PCD. In CF, early test termination may reduce measurement power with advancing pulmonary disease, suggesting differences in underlying pathophysiology. Two technically acceptable N 2 MBW runs may be sufficient in school children irrespective of diagnosis with CF or PCD. Pediatr Pulmonol. 2016;51:624–632 . © 2015 Wiley Periodicals, Inc.