Relative and absolute contributions of postprandial and fasting plasma glucose to daytime hyperglycaemia and HbA1cin subjects with Type-2 diabetes

Aims To determine the relative and absolute contributions of postprandial glucose (PPG) and fasting or preprandial plasma glucose (FPG) to daytime hyperglycaemia and HbA1c respectively, in persons with type 2 diabetes (T2DM). Methods Subjects (n = 52; 37men) had 12hr plasma glucose (PG) profiles determined in response to three serial identical test meals. PPG exposure was calculated for each meal. Excess hyperglycaemia was calculated above a PG concentration of 5.5mmol/l. Fasting hyperglycaemia was the difference between excess hyperglycaemia and PPG exposure. Subjects were divided into three groups according to HbA1c-(Gp1: 8.0%) and the relative contribution of PPG exposure and fasting hyperglycaemia to excess hyperglycaemia calculated for each meal. The absolute contribution of PPG and fasting hyperglycaemia to excess HbA1c (mean HbA1c–5.1%) was also calculated. Results The relative contributions of PPG exposure to excess hyperglycaemia for the three groups were: 58.3%, 54.3% and 35.4% (P = 0.483—Group 1 vs. Group 2; P = 0.002—Group 2 vs. Group 3) for meal 1; 69.8%, 54.7% and 23.7% (P = 0.163—Group 1 vs. Group 2; P = 0.005—Group 2 vs. Group 3) for meal 2; 85.8%, 70.2% and 48.6% (P = 0.153—Group 1 vs. Group 2; P = 0.046—Group 2 vs. Group 3) for meal 3. Absolute contributions of PPG to excess HbA1c in the three groups were 1.4%, 1.6% and 1.3% (P = NS). Conclusion The relative contribution of postprandial glucose to excess hyperglycaemia decreases as glycaemic control deteriorates, being dominant with HbA1c≤ 7.3%, irrespective of the timing of the meal during the day. However, the absolute contribution of postprandial glucose to excess HbA1c does not differ significantly (∼1.5%) with varying glycaemic control.