Ability of lung clearance index to track changes in a routine clinical CF setting

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Background: Lung clearance index (LCI) has shown to be a sensitive outcome parameter in children with cystic fibrosis (CF) for specific treatment interventions. Whether this holds true for a non-study setting is unclear. Aims: We assessed the sensitivity of LCI to track lung function decline as well as improvement in children with CF in clinical routine without specific interventions. Methods: We retrospectively analyzed multiple-breath washout measured in a clinical routine setting between 2011 and 2014 in 44 children with ≥ 3 test sessions at least one month apart. We selected children with a LCI deterioration of >10% on two consecutive visits within 12 months and assessed how many of those showed a subsequent LCI improvement of >10% within 12 months. LCI was compared to spirometry (FEV1). Results: Out of 44 children (mean (SD) age 11.4 (2.8) years), 31 children showed a LCI deterioration of >10% from mean (SD) z-scores of 5.4 (3.9) to 10.4 (4.7) compared to -1.0 (1.2) to -2.0 (1.1) FEV1 z-scores. Out of those 31 children 16 showed a subsequent LCI improvement of >10% to 4.5 (3.3) z-scores, compared to a FEV1 improvement to -0.8 (1.1) z-scores. 10 out of 16 children with >10% LCI improvement showed a parallel FEV1 improvement of >10%. A cut-off of >20% LCI change as inclusion criteria confirmed the higher sensitivity of LCI compared to FEV1. Conclusions: Not only in interventional trials but also in clinical routine measurement of children with CF, LCI seems to be more sensitive than FEV1 to assess lung function changes; both for deterioration and improvement. LCI and spirometry provide complementary functional information in children with CF.