Variability of monthly nitrogen multiple-breath washout during one year in children with cystic fibrosis.

Background: Knowledge of between-session variability of nitrogen multiple-breath washout (NMBW) indices is crucial when designing longitudinal interventional studies and in disease monitoring using NMBW as end-point. Such information is currently sparse.

Methods: Monthly triplets of NMBW were prospectively obtained from 14 children with CF during one year. Linear mixed models were used to analyze variability. Our aim was to assess between-session variability of NMBW indices from repeated measurements and compare LCI derived from different software packages currently in use (TestPoint® vs. Spiroware®).

Results: Baseline LCI (median; range) was 9.37 (6.82; 12.08). Between-session differences in LCI measurements were up to 25%. Intra Class Correlation-Coefficient was 0.82. There was no systematic difference between LCI measurements derived from the two software packages (p=0.18); however, variability was significantly higher using Spiroware®.

Conclusions: We report between-session variability of LCI using NMBW in school-age children and adolescents with CF. LCI changes exceeding 25% may be considered clinically relevant. TestPoint® and Spiroware® can be used interchangeably in longitudinal studies.