Role of plasma C-peptide determination in the management of type II diabetes.

The classification of diabetes may be sometimes difficult, particularly in persons with non-ketotic diabetes becoming manifest in middle age. The plasma C-peptide concentration, determined either in the fasting state or, preferably, after stimulation with iv. glucagon, gives a reliable estimate of the endogenous insulin secretion capacity of the individual. The C-peptide determination has improved the facilities for classification of diabetes and for appropriate choice of therapy. Patients showing stimulated plasma C-peptide values less than 0.6 nmol/l are definitely insulin-dependent, whereas values above the limit indicate that the patients can probably be managed without exogenous insulin (non-insulin-dependent diabetes). The C-peptide determination alone does not definitely indicate the therapy of choice. Conventional indicators of energy balance and glucose control together with regular follow-up of patients are still essential, particularly in the management of patients showing relatively low plasma C-peptide levels (between 0.6 and 1.1 nmol/l.). The stimulated plasma C-peptide concentration should be determined always before stopping insulin therapy in any diabetic patient or before instituting insulin therapy in a nonketotic patient. In addition, plasma C-peptide determinations will certainly prove valuable in the classification of adult onset diabetic patients for the purposes of epidemiologic studies.