Low association between fasting and OGTT stimulated glucose levels with HbA1c in overweight children and adolescents.

Background: Diabetes and prediabetes are defined based on different methods such as fasting glucose, glucose at 2-hour in oral glucose tolerance test (OGTT), and glycated hemoglobin A1c (HbA1c). These parameters probably describe different deteriorations in glucose metabolism limiting the exchange between each other in definitions of diabetes.

Objective: To investigate the relationship between OGTT and HbA1c in overweight and obese children and adolescents living in Germany.

Methods: Study population: Overweight and obese children and adolescents (n = 4848; 2668 female) aged 7 to 17 years without known diabetes. The study population was stratified into the following subgroups: normal glucose tolerance, prediabetes, diabetes according to OGTT and/or HbA1c categories, confirmed diagnosis of diabetes.

Results: In the entire study group fasting plasma glucose (FPG) correlated weakly to 2-hour glucose (r = 0.26), FPG correlated weakly to HbA1c (r = 0.18), and 2-hour glucose correlated weakly to HbA1c (r = 0.17, all P < .001). Patients with confirmed diabetes showed a very high correlation between FPG and 2-hour glucose (r = 0.73, n = 50). Moderate correlations could be found for patients with impaired fasting glucose (2-hour glucose vs HbA1c: r = 0.30, n = 436), for patients with diabetes according to OGTT and/or HbA1c (FPG vs 2-hour glucose: r = 0.43; 2-hour glucose vs HbA1c: r = -0.30, n = 115) and for patients with confirmed diabetes (2-hour glucose vs HbA1c: r = -0.47, all P < .001).

Conclusions: Because FPG, 2-hour glucose, and HbA1c correlated only weakly we propose that these parameters, particularly in the normal range, might reflect distinct aspects of carbohydrate metabolism.