Longitudinal impact of demographic and clinical variables on health-related quality of life in cystic fibrosis

OBJECTIVES: The insights that people with cystic fibrosis have concerning their health are important given that aspects of health-related quality of life (HRQoL) are independent predictors of survival and a decrease in lung function is associated with a decrease in HRQoL over time. Cross-sectional data suggest that key variables, other than lung function, are also associated with HRQoL—although study results are equivocal. This work evaluates the relationship between these key demographic and clinical variables and HRQoL longitudinally. DESIGN: Longitudinal observational study. Observations were obtained at seven time points: approximately every 2 years over a 12-year period. SETTING: Large adult cystic fibrosis centre in the UK. PARTICIPANTS: 234 participants aged 14–48 years at recruitment. OUTCOME MEASURE: Nine domains of HRQoL (Cystic Fibrosis Quality of Life Questionnaire) in relation to demographic (age, gender) and clinical measures (forced expiratory volume in 1 s, (FEV(1))% predicted, body mass index (BMI), cystic fibrosis-related diabetes, Burkholderia cepacia complex, totally implantable vascular access device, nutritional and transplant status). RESULTS: A total of 770 patient assessments were obtained for 234 patients. The results of random coefficients modelling indicated that demographic and clinical variables were identified as being significant for HRQoL over time. In addition to lung function, transplant status, age, having a totally implantable vascular access device, cystic fibrosis-related diabetes, BMI and B. cepacia complex impacted on many HRQoL domains longitudinally. Gender was important for the domain of body image. CONCLUSIONS: Demographic and changes in clinical variables were independently associated with a change in HRQoL over time. Compared with these longitudinal data, cross-sectional data are inadequate when evaluating the relationships between HRQoL domains and key demographic and clinical variables, as they fail to recognise the full impact of the CF disease trajectory and its treatments on quality of life.