Relationship between HbA1c and indices of glucose tolerance derived from a standardized meal test in newly diagnosed treatment naive subjects with Type 2 diabetes

Aims To determine the relationship between HbA(1c) and other indices of glycaemic status derived during a standardized meal tolerance test (MTT) in newly diagnosed treatment-naive subjects with Type 2 diabetes (T2DM). Methods T2DM subjects (n = 262) consumed a standard MTT in the morning after a 10-h overnight fast. Frequent samples for plasma glucose (PG) were collected over the 4-h test period. The relationship between HbA(1c) and other glycaemic indices derived from the MTT were explored. The postprandial glucose exposure was calculated as the area under the incremental plasma glucose curve above the fasting level for the test period (AUC(1)). Excess hyperglycaemia was calculated as the AUC(0-4 h) above the arbitrary PG concentrations of 6.0 mmol/l (AUC(2)) and 5.5 mmol/l (AUC(3)), respectively [upper limit of fasting normoglycaemia according to World Health Organization (WHO) and American Diabetes Association (ADA), respectively]. Fasting hyperglycaemia was also estimated, being the difference between each of the above and the postprandial excursion. The participants were divided into three subgroups according to HbA(1c) (Group 1, <= 7.0%; Group 2, 7.1-9.0%; Group 3, > 9.0%) and the relative contribution calculated of the postprandial glucose and fasting hyperglycaemia to the excess hyperglycaemia above the designated international thresholds for fasting plasma glucose. Results HbA(1c) was more strongly correlated with the fasting plasma glucose (r = 0.85, P < 0.001) than the overall postprandial glucose exposure (r = 0.539, P = 0.003). The contribution of fasting hyperglycaemia to excess hyperglycaemia using the WHO criteria for normal fasting plasma glucose for the three groups (Groups 1, 2 and 3) was 50.4%, 54.3% and 69.8%, respectively, and 57.8%, 58.8% and 71.4% using the ADA criteria. Conclusions The contribution of fasting hyperglycaemia to excess hyperglycaemia increases as glycaemic control deteriorates, becoming dominant with an HbA(1c) in excess of 7.0%. These findings indicate which therapeutic approach needs to be adopted based on the HbA(1c) of the person with T2DM.