Estimates of the relative and absolute diurnal contributions of fasting and post-prandial plasma glucose over a range of hyperglycaemia in type 2 diabetes

Abstract Aims To re-examine the relative and absolute contributions of fasting/pre-prandial glucose (FPG) and post-prandial glucose (PPG) to 24-h hyperglycaemia and HbA1c respectively in non-insulin treated subjects with type 2 diabetes (T2DM). Materials and methods A total of 52 T2DM subjects (37 men) had daytime 12 h plasma glucose (PG) profiles determined in response to three serial identical test meals commencing at 08 00 h with pre-prandial and frequent post-prandial blood samples collected. The overnight PG profile was derived by projecting the 20 00 h glucose concentration to the pre-breakfast value at 08 00 h. PPG exposure was calculated above fasting/pre-prandial value for each meal. Excess hyperglycaemia was calculated based on a PG > 5.5 mmol/L with fasting hyperglycaemia being the difference between the two measurements. The subjects were divided into five groups according to the HbA1c (Group 1 < 7.0%; Group 2: 7.0– < 7.5; Group 3: 7.5– < 8.0%; Group 4: 8.0– < 9.0%; Group 5: ≥ 9.0%). The 24 h relative contribution of PPG exposure and fasting hyperglycaemia to excess hyperglycaemia and the absolute contribution of PPG and fasting hyperglycaemia to excess HbA1c (HbA1c – 5.1%) was calculated. Results With deteriorating glycaemia, the relative contribution of PPG exposure decreased across the groups from 43.5% (HbA1c < 7.0%) to 17.8% (HbA1c ≥ 9.0%), whilst the contributions of fasting hyperglycaemia increased from 56.5% to 82.2% ( P = 0.004), respectively. The absolute contributions of PPG to excess HbA1c was 0.7%, which remained relatively stable across the spectrum of HbA1c , whilst fasting hyperglycaemia increased significantly from groups 1 to 5 ( P < 0.001). Conclusions Fasting hyperglycaemia contributes substantially in all groups, increasing as HbA1c deteriorates. The absolute contribution of PPG to excess HbA1c did not vary across the range of HbA1c , representing a significant relative contribution even in well-controlled subjects with a HbA1c < 7.0%.