One-Hour Meal Tolerance Test to Assess Withdrawal of Insulin Therapy in Overweight Patients With Type 2 Diabetes

Abstract

To evaluate the clinical usefulness of a 1-hour meal tolerance test to determine the feasibility and safety of discontinuation of insulin therapy in overweight, insulin-treated patients with type 2 diabetes mellitus. Overweight patients who presented with metabolic decompensation at initial diagnosis of type 2 diabetes were hospitalized and treated with insulin. A 1-hour meal tolerance test was performed in an outpatient setting when patients had maintained a stable metabolic status with decreasing daily insulin requirement and the possibility of withdrawal of insulin therapy was considered. After an overnight fast, venous blood samples were collected before and 1 hour after consumption of an oral liquid meal (240 mL, 240 kcal, approximately 30 g of sucrose) to measure glucose and C-peptide levels. If the postmeal glucose level was < or = 10 mmol/L, the insulin therapy was discontinued. Patients underwent follow-up to validate the clinical decision. Twenty-four overweight adult Mexican American patients (8 of whom had ketoacidosis) were treated with insulin at initial diagnosis of type 2 diabetes. The mean insulin dosages were reduced progressively from 71 +/- 8 U/day to 31 +/- 3 U/day during a period of 4 +/- 0.5 months. At that stage, the mean fasting and 1-hour postmeal blood glucose levels were 5.0 +/- 0.2 mmol/L and 8.4 +/- 0.4 mmol/L, respectively. Meal-induced plasma C-peptide levels showed 1.9- to 4-fold increases, confirming substantial endogenous insulin secretion. The C-peptide responses were similar in the two subgroups of patients with or without initial ketoacidosis. On the basis of postmeal blood glucose levels, the insulin therapy was discontinued in all cases. After 3 months of follow-up, all patients were in good metabolic control. Fourteen patients underwent follow-up for >12 months; 10 of them were maintained without antidiabetic medications for 21.4 +/- 2.8 months. Two patients were treated with sulfonylurea drugs after 4 months, and another two required insulin therapy by the 4th and 18th months, respectively. A 1-hour postmeal blood glucose level is helpful for deciding the withdrawal of insulin therapy in overweight, insulin-treated patients with type 2 diabetes.