Glucagon-C-peptide test as a measure of insulin requirement in type 2 diabetes: evaluation of stopping insulin therapy in eleven patients.

The glucagon-C-peptide test was evaluated as a predictor of the requirement of insulin therapy in type 2 diabetes mellitus. Endogenous insulin secretory capacity was measured in a population of 150 insulin-treated adult diabetic patients by determining postprandial glucagon-stimulated plasma C-peptide concentration (Novo, antiserum M 1230). Eleven subjects with C-peptide levels above 1.0 nmol/l comprised the subgroup in which the previously started insulin therapy was discontinued. After an observation period of a week in hospital the metabolic control of the patients was followed in an outpatient clinic for twelve months. During the observation period one patient was managed on diet alone, eight subjects required oral hypoglycaemics agents and two required the reinstitution of insulin therapy. Mean fasting blood glucose and GHbA1 (glycosylated haemoglobin) of non-insulin dependent diabetics increased during the observation period (from 8.8 to 11.8 mmol/l, p less than 0.001, and from 12.2 to 14.1%, p less than 0.05, respectively). No significant changes were found in total or HDL-cholesterol or triglyceride levels. The findings demonstrate that the glucagon-C-peptide test can be used as an aid in judging whether the withdrawal of insulin may be considered without excessive risk of developing diabetic ketoacidosis. However, the test cannot be used as the only criterion when assessing the need for exogenous insulin in type 2 diabetes. Meticulous monitoring of blood glucose levels is necessary when insulin therapy is withdrawn, because diabetic patients with peripheral insulin resistance may not maintain satisfactory glycaemic control without exogenous insulin despite of high residual endogenous insulin secretion.