The Relationship between Plasma Glucose Concentration and Hemoglobin A1c during a Standardized Meal Tolerance Test in Individualss with Type 2 Diabetes

Abstract

Background: The aims of this study were to assess plasma glucose concentration and the extent of excursion during a standardized meal tolerance test (MTT), and to evaluate the relationship between glycosylated hemoglobin (HbA1c) and plasma glucose concentration at different times of the day in patients with type 2 diabetes. Methods: One hundred seventy-two patients (age, 57.3±0.8 years; HbA1c, 7.8%±0.1%) with type 2 diabetes were assigned to receive a standardized MTT after a 10-hour overnight fast. Meals were provided at 8:00 A.M. and 12:00 P.M. Plasma glucose concentration was determined at 8:00 A.M. (before breakfast) and then at hourly intervals until 4:00 P.M. HbA1c concentrations were determined in all patients. Results: HbA1c level correlated significantly with daily plasma glucose concentration during the standardized MTT (r=0.49-0.71; all P＜0.001). The correlation coefficient was higher after lunch (r=0.517, P＜0.001) than before lunch (r=0.175, P=0.025) in patients with type 2 diabetes. In patients with HbA1c＜7.0%, the correlation between HbA1c and the incremental area under the curve (IAUC) was higher before lunch (r=0.408, P=0.004) than after lunch (r=0.259, P=0.090). In contrast, in patients with HbA1c＞8%, the correlation between IAUC and HbA1c was stronger after lunch (r=0.465, P=0.001) than before lunch (r=-0.230, P=0.074). Conclusions: In general, HbA1c level correlated significantly with daily plasma glucose concentration during a standardized MTT in patients with type 2 diabetes; the correlation was stronger after lunch than before lunch. The plasma glucose response to a meal correlated with HbA1c better before lunch in patients with HbA1c＜7.0%, whereas the correlation was stronger after lunch in patients with poor glucose control and HbA1c＞8.0%.