Background: Primary ciliary dyskinesia (PCD) is a genetic disorder, in which impaired airway mucociliary clearance and recurrent respiratory tract infections ultimately lead to bronchiectasis and lung function decline. Lung clearance index (LCI), as measured by multiple breath washout (MBW), is a marker of ventilation inhomogeneity. Recent studies have shown an abnormal increase of LCI in patients with PCD.

Aims and Objectives: We aim to systematically review the literature to describe the alterations of LCI in PCD and further compare it with FEV₁, which is the gold-standard marker of lung functional impairment.

Methods: The database PubMed was systematically searched for studies including the measurement of LCI in PCD patients by the end of 2022. Review articles or studies including overlapping populations were excluded.

Results: Among 250 results, a total of 19 eligible studies were found. After excluding those with overlapping populations, 9 studies were further analysed. The studies were run from 2013 to 2022, and cumulatively included 273 PCD patients (38.6% males) aged from 2.2 to 41 years. MBW was performed via the ultrasonic flowmeter Exhalyzer^® D in 8 studies and the photoacoustic gas analyser Innocor^® in one study. Interestingly, in all studies mean or median LCI was significantly increased compared to healthy controls, whereas only in one study the mean or median FEV₁ z-score was significantly decreased (<-1.96).

Conclusions: MBW gains ground in daily clinical practice for PCD, and, from a systematic search of the literature, LCI appears to be a sensitive marker of lung function decline in the early stages of the disease.