[Carbohydrate metabolic changes in cystic fibrosis]

Abstract

Objectives: To assess the prevalence of impaired glucose tolerance and diabetes mellitus in a group of patients with cystic fibrosis and to compare insulin secretion, haemoglobin A1c, age, gender, genotype, and clinical status related variables between the groups with abnormal (impaired glucose tolerance and diabetes mellitus) and normal carbohydrate metabolism.

Patients and methods: 66 patients with cystic fibrosis (age 1-38 years). Plasma glucose, insulin and C peptide determinations during an oral glucose tolerance test (OGTT) in 65 patients (one was previously known as diabetic). Based on the Expert Committee from the American Diabetes Association (1997), patients were classified as having impaired glucose tolerance and diabetes mellitus. Haemoglobin A1c, presence of delta F508 mutation, date of diagnosis and first sputum colonization, scores of National Institutes of Health, Schwachman and Chrispin-Norman, pancreatic enzyme intake, weight, body mass index, forced expiratory volume in one second and forced vital capacity determinations in every patient. Comparative analysis of these variables in both groups of patients was performed by Student test.

Results: Nine patients (13.6%) showed impaired tolerance glucose and one diabetes mellitus following OGTT, so we have two diabetics in our cystic fibrosis group (3.0%). When compared to cystic fibrosis patients with normal glucose tolerance, tolerance glucose and diabetes mellitus patients had significantly reduced basal insulin levels (8.6 [3.8] vs 15.0 [22.2] microU/ml; p < 0.0001), increased glucose stimulated insulin and C peptide levels (50.2 [19.3] vs 21.4 [19.3] microU/ml; p < 0.0001, and 9.0 [5.9] vs 4.4 [3.2] ng/ml; p < 0.0001), they were older (18.0 [7.5] vs 12.7 [7.3] years old; p < 0.05) and had longer time since diagnosis and since first sputum colonization. The remaining variables did not differ between the two groups. All patients with exocrine pancreatic sufficiency showed normal glucose tolerance.

Conclusions: Abnormalities in carbohydrate metabolism were present in 16.6% of cystic fibrosis patients. These patients had reduced basal but increased glucose stimulated insulin levels. Age, time since diagnosis of cystic fibrosis, time since first sputum colonization and exocrine pancreatic insufficiency are the variables being associated with carbohydrate metabolism abnormalities.