Objectives: To study prevalence and incidence of diabetes mellitus in patients with cystic fibrosis.
Design: Five year prospective study with annual oral glucose tolerance tests.
Setting: CF Center Copenhagen, Denmark.
Subjects: 191 patients with cystic fibrosis aged above 2 years.
Main outcome measures: Glucose tolerance, plasma glucose concentrations after fasting and after glucose loading, and haemoglobin A1c levels.
Results: Prevalence of diabetes increased from 11% (n = 21) to 24% (n = 46) during study, with annual age dependent incidence of 4-9%. Diabetes was diagnosed at median age of 21 (range 3-40). At diagnosis of diabetes, symptoms of hyperglycaemia were present in 33% of patients, fasting hyperglycaemia (> or = 7.8 mmol/l) was seen in 16%, and increased haemoglobin A1c levels (> 6.4%) were seen in 16%. Impaired glucose tolerance implied higher risk for development of diabetes than normal glucose tolerance (odds ratio 5.6). In 58% of cases with impaired glucose tolerance, however, glucose tolerance was normal at next annual test. Normal glucose tolerance was found in only 37% of patients at all five tests. Within this group of patients, median plasma glucose concentrations after fasting and after glucose loading and haemoglobin A1c levels increased by 6-8% during study.
Conclusions: Prevalence and incidence of diabetes in cystic fibrosis patients was high and increased with age. Since hyperglycaemic symptoms, fasting hyperglycaemia, and increased levels of glycated haemoglobin did not reliably identify diabetes mellitus, we recommend annual oral glucose tolerance tests in all cystic fibrosis patients aged over 10 years.