Repeatability of Multiple Breath Washout in Pediatric Primary Ciliary Dyskinesia.

Background: Primary ciliary dyskinesia (PCD) is a motile ciliopathy characterized by abnormal mucociliary clearance and progressive lung disease. Spirometry is commonly used to monitor lung health and response to treatment, but it is known to be insensitive to early subclinical lung disease in PCD. Multiple breath washout is more sensitive than spirometry, but its repeatability in PCD has not been assessed.

Objectives: To evaluate the (i) same-day and (ii) 28-day repeatability of lung clearance index 2.5% (LCI) in PCD.

Methods: Participants > 6 years old with a confirmed PCD diagnosis were recruited from two Canadian PCD centers. Participants completed baseline lung function tests to measure their forced expiratory volume in 1-second, z-score (FEV1z), and LCI. Tests were repeated either on the same day or after 28 days. No clinical interventions were performed during the same-day repeat testing. Outpatient therapies were unchanged during 28-day repeat testing. Repeatability was assessed using intraclass correlation (ICC), and Bland-Altman plots (B&A).

Results: Twenty-three participants were enrolled (same-day: 16; 28-day: 13). The same-day and 28-day repeat testing ICC for FEV1z were 0.9 and 0.92, and LCI were 0.95 and 0.71, respectively. Baseline testing showed that most participants had abnormal LCI (18 of 29 tests), even in those with FEV1z in the normal range. FEV1z and LCI exhibited a weak inverse correlation.

Conclusions: LCI is a repeatable and sensitive lung function measure in PCD patients, and may be a suitable outcome metric for clinical trials, particularly in patients with early subclinical lung disease.