Introduction In cystic fibrosis, lung clearance index (LCI) is a sensitive predictor of CT scan determined lung pathology. In bronchiectasis (BE) there is a need for improved markers of lung function to gauge disease severity and response to interventions in clinical trials.

Aims To assess if LCI is a repeatable and superior predictor of CT scan abnormalities compared with FEV₁ in BE.

Methods 60 patients with stable BE were recruited. LCI (using SF₆ multiple breath washout), spirometry and CT scores were collected. Health related quality of life (HRQoL) was measured using the St. George’s Respiratory Questionnaire. A separate group of 30 BE patients were recruited and LCI, spirometry and HRQoL were assessed when clinically stable on 2 occasions, 2 weeks apart.

Results Mean (SD) age was 62 (10) years, FEV₁ 76.5 (18.9)% predicted, LCI 9.1 (2.0) and total CT score 14.1 (10.2)%. FEV₁ negatively correlated with LCI (r = -0.51, p < 0.0001.) Across all CT score subscales, there was clear evidence of a relationship with LCI, with no or very weak evidence of any additional effect of FEV₁. The strongest correlations of subgroup CT scores with LCI were seen in),% parenchymal score (r = 0.56, p < 0.001),% mucus plugging (r = 0.49, p < 0.001),% total score (r = 0.55, p < 0.001)% bronchiectasis (r = 0.41, p < 0.01. There was no association for either FEV₁ or LCI with% airway thickening and for % bronchiectasis score and FEV₁. There were no significant associations between LCI or FEV₁ and HRQoL. The inter-visit ICC for LCI was 0.94 (95% CI 0.89 to 0.97, p < 0.001).

Conclusions LCI is a valid and repeatable test of lung function in BE. It is a superior predictor of lung function than FEV₁ in the detection of abnormalities demonstrated on CT scan. LCI is a useful test in patients with early lung disease or those with preserved spirometric scores. LCI also has the potential to be an alternative outcome measure to spirometry in clinical trials.