Background Primary ciliary dyskinesia (PCD) is a rare disease, characterised by chronic airway infection. In cystic fibrosis, FEV₁ is insensitive to detect patients with structural damage, and Lung Clearance Index (LCI) was proposed as a better marker of early lung damage. In PCD, the relationship between functional and structural abnormalities has been less studied. We aimed to re-examine this in a cohort of children and adults with mild to moderate PCD.

Methods Thirty-eight patients with PCD (5.2–25.0 years) and 70 healthy controls (4.4–25.8 years) were recruited to compare LCI, measured by N₂ multiple breath washout and FEV₁ in a prospective observational trial. In a subset of 30 patients who underwent chest imaging, structural abnormalities were evaluated with cystic fibrosis computed tomography (CFCT) scores.

Results LCI was abnormal in 28 of 38 patients and a moderate correlation was observed between LCI and FEV₁ (r=−0.519, p=0.001). Moreover, LCI correlated well with CFCT total score (r=0.800, p<0.001) and also with subscores for airway wall thickening (r=0.809, p<0.001), mucus plugging (r=0.720, p<0.001) and bronchiectasis (r=0.494, p<0.001). Concordance was seen between LCI and CFCT in 25 of 30 (83%) patients, but between FEV₁ and CFCT in only 16 of 30 (53%) patients. LCI was more sensitive (90.9%, 95% CI 70.8 to 98.6) to detect patients with structural abnormalities than FEV₁ (36.4%, 95% CI 17.2 to 59.3).

Conclusions We demonstrated that measuring LCI in patients with PCD is of clinical relevance; it was more frequently abnormal than FEV₁, correlated well with CFCT and was more sensitive than FEV₁ to detect patients with structural abnormalities.