Relative and absolute contributions of postprandial and fasting plasma glucose to daytime hyperglycaemia and HbA1c in subjects with Type 2 diabetes

Abstract

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:<7.3%;Gp2:7.3%-8.0%;Gp3: >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. © 2009 Diabetes UK.