Relationship between glycosylated hemoglobin and β-cell function

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Objective To assess the relations between glycosylated hemoglobin A1c(HbA1c) and β-cell function as measured by indices derived from oral glucose tolerance test (OGTT) in Chinese subjects. Methods A total of 913 subjects, who underwent 75 g OGTT for evaluation of glucose intolerance from June 2010 to February 2013, were included. According to OGTT, the enrolled subjects were divided into the following three groups: normal glucose tolerance (NGT, n=205), impaired glucose regulation (IGR, n=328), and type 2 diabetes mellitus (T2DM, n=380). Meanwhile, the subjects were also divided into three groups according to HbA1c levels: HbA1c 6.4% (n=245). Insulin sensitivity was measured by Matsuda insulin sensitivity index (ISIM) and 1/homeostasis model assessment of insulin resistance (1/HOMA-IR). β-cell function adjusted by insulin sensitivity was assessed from disposition index (DI) at early-phase DI30 and total DI120. ANOVA, Chi-Square test and general linear model were used for data analysis. Results Compared with the HbA1c 6.4% group (F=12.765-317.316, all P<0.05). In NGT group, DI30 and DI120 decreased in subjects with elevated HbA1c; in HbA1c<5.7% group, DI30 and DI120 declined as glucose increased. Conclusions Both impairment of β-cell function and insulin sensitivity contributes to the deterioration of HbA1c in Chinese population. A combination of HbA1c and OGTT is effective in screening for subjects with β-cell dysfunction. Key words: Diabetes mellitus, type 2; Glycated hemoglobins; β-cell function