BACKGROUND: The widespread availability of genetic testing allowing the identification of “milder” individuals with CF coincided with improvements in CF life expectancy but the relative contribution of case mix to that improved survival is uncertain.
METHODS: Patients in the U.K. CF registry were divided into ‘mild phenotype’ defined as pancreatic sufficient and ‘typical CF’ defined as pancreatic insufficient. Distributions of age at death were compared with Mann-Whitney test. Temporal trends in incidence and prevalence were described. Jonckheere-Terpstra test was used to compare the trend for median age at death from 2007 to 2010.
RESULTS: Patients with ‘mild phenotype’ had significantly higher age at death (32 years, interquartile range 14 years versus 27 years, interquartile range 29 years; Mann-Whitney test p-value = 0.026). The proportion of patients with ‘mild phenotype’ appeared to be increasing (0.128 in 2007, 0.144 in 2010). The trend for increasing age at death (from 25 years in 2007 to 29 years in 2010, Jonckheere-Terpstra test p-value = 0.012) was independent of the ‘mild phenotype’ patients.
CONCLUSION: The impact of mild phenotypes on the improvement in the median age at death among people with CF was trivial.