The relationship between glycosylated haemoglobin (HbA1c) and measures of insulin resistance across a range of glucose tolerance

Aim. This study aimed to assess the correlation between HbA1c and insulin resistance as measured by a variety of different indices in subjects from across the glycaemic spectrum. Methods. Subjects with normal glucose tolerance (NGT; n = 24), impaired fasting glucose (IFG; n = 12), impaired glucose tolerance (IGT; n = 12), and type 2 diabetes (DM; n = 13) were studied. All had specimens taken in the context of a standard oral glucose tolerance test at their first visit and had the insulin sensitivity parameter (Si) determined by frequently-sampled intravenous glucose tolerance test at a second visit. Results. HbA1c was more strongly associated with Si in NGT (r = - 0.65) than in IFG (r = - 0.48). Compared to other indices of insulin resistance HbA1c has minimal overlap in values (0.0%) between NGT and subjects with type 2 diabetes. Conclusions. HbA1c can be used as a simple and reliable marker of insulin resistance in NGT adults with relatively high insulin sensitivity.