Classic Respiratory Disease but Atypical Diagnostic Testing Distinguishes Adult Presentation of Cystic Fibrosis

BackgroundThe majority of new cases of cystic fibrosis (CF) are diagnosed before age 2 years. Diagnoses in older individuals have increased because of improved genetic testing and increased awareness of the disease. A comprehensive description of clinical, genetic, and microbiologic characteristics of adult-age presentation of CF does not exist. We compare newly diagnosed CF in adults with newly diagnosed CF in children and adolescents in the United States.MethodsThis is a cross-sectional study of new CF diagnoses from the Cystic Fibrosis Foundation Patient Registry between 1995 and 2005. Diagnostic, microbiologic, and clinical features during year of diagnosis were analyzed for subjects by age group. Descriptive statistics were calculated for variables on characteristics by age group.ResultsA total of 9,766 new diagnoses of CF were reported to the Registry between 1995 and 2005. The proportion of adult diagnoses increased significantly in the years 2001 to 2005 as compared with 1995 to 2000 (9.0% vs 7.7%, P = .012). FEV1% predicted decreased with increasing age at diagnosis (P < .001). Infection with Pseudomonas aeruginosa was most common in adults (P < .001). Both the number of positive sweat chloride tests and prevalence of ΔF508 mutation, the most common mutation in the United States, decreased significantly with older age at diagnosis (P < .001).ConclusionsBetween 1995 and 2005, the proportion of new diagnoses of CF in adults in the United States increased significantly. Adults present with commonly described CF respiratory disease (Pseudomonas aeruginosa infection and reduced lung function), but have lower sweat chloride values and lower frequency of ΔF508 mutation. Knowledge of clinical characteristics and diagnostic limitations of adult patients presenting with CF will hopefully lead to earlier recognition and intervention.