Oral glucose tolerance test with prolonged determination of glucose, insulin and C-peptide levels in patients with Cystic Fibrosis

Rationale: In literature the value of early diabetic therapy in patients with Cystic Fibrosis (CF) developing diabetes is considered of major interest. Still, no consensus is available on the optimal diabetic treatment of CF patients with either a normal or impaired glucose tolerance. To get more insight in the exact glucose levels and the total insulin secretion, as well as to determine the optimal time of measurement peak glucose levels we would like to perform prolonged oral glucose tolerance test (OGTT) with insulin and C-peptide measurements in these patients, from what areas under the curve, insulin resistance and ß-cell function will be calculated
Objective: Investigate the exact glucose levels during a two hour OGTT and a follow-up period of three hours. At the same time, insulin and C-peptide levels are determined to get more insight in the total insulin secretion.

Study design: Prospective clinical comparing experiment with defined patient populations.

Study population: The patient population comprises 6 adult CF patients with exocrine pancreas sufficiency, 6 adult CF patients with exocrine pancreas insufficiency and a normal glucose tolerance, and 6 adult CF patients with exocrine pancreas insufficiency and an impaired glucose tolerance.

Main study parameters/endpoints: Blood glucose levels and blood insulin levels and blood C-peptide levels during an 2 hour OGTT and during a follow-up period of 3 hours. Samples are taken on pre-set times.
Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Subjects will have to visit our clinic one time in the total scope of this study. At this visit, they will undergo physical examination by determination of body temperature, blood pressure and pulses and will be questioned about their present clinical status. A venflon is placed in an antecubital vein and will stay in place during the total 5 hours. During this period of 5 hours, subjects have to stay sober. A total of 10 blood samples of each 4,0 ml will be taken.

The study period for the individual patient comprises one outpatient visit of 6 hours.

All subjects included into this study will be administered in the hospital after three days of high carbohydrate intake and an overnight fasting of at least 8 hours. Subjects will be questioned about their present clinical status. In all subjects temperature, pulses and blood pressure will be determined.

After a 15-min period of acclimatizing, a venflon is placed in an antecubital vein. A glucose solution of 1,75 gr/kg with a maximum of 75 grams of glucose is orally administered to the subjects. Blood samples of 4,0 ml each in a serum tube are taken on pre-set times, i.e. -5, 0, 30, 60, 90, 120, 150, 180, 240, and 300 min after administering the glucose solution.
Patients stay sober during the total scope of the study.