Objective: Diabetes is increasingly common in cystic fibrosis, but little information describing its influence on mortality exists. Using national U.K. data, in this study we document diabetes-specific mortality rates, estimate the impact of diabetes on survival, and estimate population-attributable fractions.
Research design and methods: This retrospective cohort study identified 8,029 individuals aged 0-65 years from the U.K. Cystic Fibrosis Registry (1996-2005). A total of 5,892 patients were included in analyses of mortality rates, and 4,234 were included in analyses of risk factors. We calculated age-adjusted mortality rates using Poisson regression, standardized mortality ratios using the population of England and Wales, and relative risks using proportional hazards modeling.
Results: During 17,672 person-years of follow-up, 393 subjects died. The age-adjusted mortality rate was 1.8 per 100 person-years (95% CI 1.6-2.0). The age-adjusted mortality rates per 100 person-years were 2.0 (1.8-2.4) in female subjects and 1.6 (1.4-1.9) in male subjects, and 4.2 (3.4-5.1) in individuals with diabetes vs. 1.5 (1.3-1.7) in those without diabetes. Independent risk factors for death included diabetes (hazard ratio 1.31 [95% CI 1.03-1.67], female sex (1.71 [1.36-2.14]) plus poorer pulmonary function, lower BMI, Burkholderia cepacia infection, absence of Staphylococcus aureus infection, allergic bronchopulmonary aspergillosis, liver disease, prior organ transplantation, and corticosteroid use.
Conclusions: Individuals with cystic fibrosis die earlier if they have diabetes, which, if delayed or better treated, might reasonably extend survival; this hypothesis merits testing.