Chronic hyperglycemia but not glucose variability determines HbA1c levels in well-controlled patients with type 2 diabetes

To determine the relationships between HbA1c, characteristics of hyperglycemia and glycemic variability in well-controlled type 2 diabetes (HbA1c < 7.0%), we studied 63 primary-care patients (36 men and 27 women), aged 34–75 years, with type 2 diabetes for 2–32 years using a continuous glucose monitoring system (CGMS) and standardized meal test (MMT).Duration of hyperglycemia (>8.0 mmol/l), standard deviation score (S.D.-score) and mean amplitude of glycemic excursions (MAGE) were analyzed from CGMS data and postprandial glucose during MMT (PPGMMT).Patients were hyperglycemic for 5.7 h/day (median), experienced 4.1 hyperglycemic episodes/day, and 78% exceeded PPG levels of 8.0 mmol/l. HbA1c, though associated with the extent of hyperglycemia (r = 0.40, p < 0.001), failed to correlate with S.D.-score and MAGE. Multiple regression analysis demonstrated that HbA1c was predicted only by fasting glucose (R2 = 0.24, p < 0.001) but neither by PPGMMT, duration of hyperglycemia, S.D.-score nor MAGE.CGMS and meal test provide the tools for complete characterization of glycemia in type 2 diabetes.In well-controlled type 2 diabetes, HbA1c correlates with chronic hyperglycemia but not with glucose variability. Our data suggest that chronic sustained hyperglycemia and glucose fluctuations are two independent components of dysglycemia in diabetes.