Inter-test reproducibility of lung clearance index in adults with clinically stable CF and in healthy controls

- Multiple breath nitrogen washouts (N₂ MBW) and its derived lung clearance index (LCI) are increasingly used in clinical applications, due in part to the availability of commercial equipment. However, there are limited longitudinal data describing inter-test reproducibility for tests performed in adults.

- Nitrogen MBWs were performed in triplicate in 41 subjects with clinically stable CF and in 56 healthy controls with normal spirometry. Functional residual capacity (FRC), LCI and alveolar mixing efficiency (AME) measurements were obtained during two visits separated by 3-6 weeks using a commercial device.

- At both visits, LCI was significantly higher and AME significantly lower in the CF group than in the healthy controls. There was no significant difference in FRC between the two groups. The average actual difference in all three MBW parameters between visits were close to zero in both groups. The biological variability of LCI (AME) was ±15 % (±4 %) in controls and ±18 % (±9 %) in the CF group.

- The reproducibility of LCI and AME between sessions separated by 3-6 weeks is similar in healthy and clinically stable CF adults. Our findings further suggest that, for the commercial device used in this study, a percentage change in LCI greater than ±15 % can be considered physiologically relevant and greater than the biological variability of the test.