Impact of glucagon response on early postprandial glucose excursions irrespective of residual β‐cell function in type 1 diabetes: A cross‐sectional study using a mixed meal tolerance test

AIMS/INTRODUCTION: Controlling postprandial glucose levels in patients with type 1 diabetes is challenging even under the adequate treatment of insulin injection. Recent studies showed that dysregulated glucagon secretion exacerbates hyperglycemia in type 2 diabetes patients, but little is known in type 1 diabetes patients. We investigated whether the glucagon response to a meal ingestion could influence the postprandial glucose excursion in patients with type 1 diabetes. MATERIALS AND METHODS: We enrolled 34 patients with type 1 diabetes and 23 patients with type 2 diabetes as controls. All patients underwent a liquid mixed meal tolerance test. We measured levels of plasma glucose, C‐peptide and glucagon at fasting (0 min), and 30, 60 and 120 min after meal ingestion. All type 1 diabetes patients received their usual basal insulin and two‐thirds of the necessary dose of the premeal bolus insulin. RESULTS: The levels of plasma glucagon were elevated and peaked 30 min after the mixed meal ingestion in both type 1 diabetes and type 2 diabetes patients. The glucagon increments from fasting to each time point (30, 60 and 120 min) in type 1 diabetes patients were comparable to those in type 2 diabetes patients. Among the type 1 diabetes patients, the glucagon response showed no differences between the subgroups based on diabetes duration (<5 vs ≥5 years) and fasting C‐peptide levels (<0.10 vs ≥0.10 nmol/L). The changes in plasma glucose from fasting to 30 min were positively correlated with those in glucagon, but not C‐peptide, irrespective of diabetes duration and fasting C‐peptide levels in patients with type 1 diabetes. CONCLUSIONS: The dysregulated glucagon likely contributes to postprandial hyperglycemia independent of the residual β‐cell functions during the progression of type 1 diabetes.