Correlations between A1c, fasting glucose, 2h postload glucose, and β-cell function in the Chinese population.

This study was aimed to assess the associations of hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), and 2h postload plasma glucose (2hPG) with β-cell function in the Chinese population. A total of 913 subjects underwent 75-g oral glucose tolerance test (OGTT) and HbA1c testing. According to OGTT, isolated impaired fasting glucose (i-IFG) was defined as 5.6 mmol/l ≤ FPG < 7.0 mmol/l and 2hPG < 7.8 mmol/l; isolated impaired glucose tolerance (i-IGT) was defined as FPG < 5.6 mmol/l and 7.8 mmol/l ≤ 2hPG < 11.1 mmol/l. HbA1c 5.7-6.4 % was used to identify subjects with prediabetes. Insulin release was calculated by basal homeostasis model assessment of insulin secretion (HOMA-β), early-phase InsAUC30/GluAUC30, and total-phase InsAUC120/GluAUC120. β-cell function relative to insulin sensitivity was expressed as disposition index (DI). All indices of insulin sensitivity and β-cell function gradually decreased with increasing HbA1c, FPG, and 2hPG (all p < 0.01). β-cell function decreased precipitously when HbA1c exceeded 5.5 %. Compared with HbA1c, FPG showed stronger correlations with HOMA-β, InsAUC30/GluAUC30, InsAUC120/GluAUC120, DI30, and DI120 (all p < 0.05), and 2hPG was more closely related to DI30 and DI120 (all p < 0.01). Moreover, FPG was more strongly related to HOMA-β and InsAUC30/GluAUC30 than 2hPG (all p < 0.05). The combination of i-IFG and HbA1c 5.7-6.4 % showed the greatest reduction in DI30 and DI120 compared with HbA1c 5.7-6.4 % alone, i-IGT, or i-IFG (p < 0.05). In conclusion, HbA1c could be used as a marker to identify subjects with impaired β-cell function, but OGTT performs better than HbA1c. The combination of HbA1c and FPG is a simple and sensitive method to evaluate β-cell function.