Background~Lung function measurements are commonly used in PCD to monitor disease progression. Spirometry measurements are taken every 3 months and results are compared to established references, adjusted for age, height and ethnicity. Results are also compared to previous measurements from the same patient at earlier appointments. However, little is understood of the impact of intra-individual variability and the extent of spontaneous variations in these comparisons.~One of the priorities for respiratory research in the UK is to understand factors involved in determining different outcomes for lung function.[1] The precision of measurements done on the same individual conducted by different people, in different settings and using different equipment is not entirely known. Importantly, previous studies in healthy children assessing intra-individual variability have shown variations of up to 1.2 z-scores in spirometry parameters over the course of 1 year.[2] Within test-variability and daily repeatability can range from 2 to10% FEV% predicted in young healthy children.[3],[4]~In PCD, deterioration of lung function does not follow a pre-defined pattern.[5] However, none of the published studies on lung function in PCD to date have taken into consideration the imprecision of individual and repeated measurements on the same individual over time. Personal experience and unpublished small retrospective assessments suggest that there is considerable variability.~Key research question~Quantify intra-individual (i.e. in the same individual) variations between measurements of lung function in stable patients with primary ciliary dyskinesia (PCD), a rare genetic disease that causes lung damage.~Study design~Prospective multicentre cohort study using routinely collected clinical data to evaluate natural variability of lung function measurements in stable PCD patients.~The primary end-point is to assess intra-individual variations between repeated measures of lung function parameters. Secondary end-points include: a) Inter-individual variations between repeated measures of lung function parameters and correlations with baseline measures; b) intra- and inter-individual variation between repeated measures of lung function parameters during exacerbation.~Participants will be approached by their clinicians and asked to sign a consent form to allow for their anonymised routinely collected clinical data to be entered into the study. Routine clinical data will be collected at PCD follow-up clinics in participating centres. These data are already collected for clinical purposes and will be anonymised locally. Non-identifiable data will be entered into the study database by a member of the clinical team of the participating centre. The study coordinating centre (University of Southampton) will only have access to the anonymised dataset.~The data collection period will last 18 months (6 months for patients recruitment and 12 months for patient follow-up).
Using routinely collected clinical data, this study aims to quantify intra-individual (i.e. in the same individual) variations between measurements of lung function in stable patients with primary ciliary dyskinesia (PCD), a rare genetic disease that causes lung damage.