No changes of insulin sensitivity in cystic fibrosis patients with different degrees of glucose tolerance: an epidemiological and longitudinal study

Department of Internal Medicine, University of Messina, Italy.

Plasma glucose and insulin responses to oral glucose and insulin sensitivity by the euglycemic hyperinsulinemic clamp technique were investigated in 30 cystic fibrosis patients with normal fasting blood glucose levels and normal (N = 12), impaired (N = 12) or diabetic (N = 6) glucose tolerance, and in 12 control subjects. In a subgroup of 10 cystic fibrosis patients with non-diabetic glucose tolerance both oral glucose tolerance test and clamp were performed again 48-52 months later. Following oral glucose, glycemic responses were higher in cystic fibrosis patients than in controls, whereas insulin responses were reduced significantly only in the patients with diabetic glucose tolerance. Insulin sensitivity did not differ significantly in the patient subgroups with different degrees of glucose tolerance and in controls. In the 10 patients who underwent a 4-year follow-up, insulin responses to oral glucose decreased significantly, whilst insulin sensitivity did not change substantially. Insulin sensitivity persisted unmodified even in the patients with deteriorating glucose tolerance. No correlation were observed between metabolic data and clinical status of patients. In conclusion, in cystic fibrosis subjects with fasting euglycemia and different degrees of glucose tolerance: (i) insulin sensitivity is not impaired; (ii) eventually changes of glucose tolerance over time are not associated with modifications of insulin sensitivity; (iii) insulin secretion deteriorates over time even in the patients with stable glucose tolerance; (iv) eventual deterioration of both glucose tolerance and insulin secretion is not linked to a worsening of either nutritional or clinical parameters.