Objective: To evaluate plasma C-peptide levels in middle-aged and elderly patients with type II diabetes, to clarify their practical use in assessing the need for insulin therapy, and to determine their sensitivity in distinguishing insulin-requiring from non-insulin-requiring diabetes after improved baseline glycemic control.
Methods: Plasma glucose and C-peptide levels were measured in a fasting state and 2 hours after an oral challenge with 100 g of glucose in groups of obese and normal-weight, glycemic-controlled, middle-aged and elderly patients with diabetes treated with insulin or an orally administered hypoglycemic agent (OHA). Basal and glucose-stimulated C-peptide levels as well as increased stimulated glucose values were contrasted in insulin- versus OHA-treated groups. In a second protocol, basal and glucose-stimulated C-peptide reactivity and stimulated glucose levels were also measured in eight patients with diabetes, before and after glycemic control.
Results: Irrespective of the age difference, stimulated C-peptide levels in the insulin-treated patients were significantly lower than those in the weight-matched OHA patients. Similarly, for both the middle-aged and elderly patients, stimulated glucose levels and degree of glucose elevation were higher in the insulin-treated patients. In the second protocol, as hyperglycemia was reduced, beta-cell secretion measured by C-peptide responses to glucose was significantly increased, in conjunction with a decrease in the stimulated glucose levels.
Conclusion: These results indicate that measurements of C-peptide responses to glucose stimulation are helpful to determine the decision to use insulin in both elderly and middle-aged patients with diabetes. Blunted insulin responses identify those patients who require insulin treatment, whereas high C-peptide values in insulin-treated patients suggest the possibility of discontinuing insulin therapy.