Background: Achieving fasting plasma glucose (FPG) target may not reflect hemoglobin A1c (HbA1c) target achievement.

Objective: Illustrate the blood glucose patterns contributing to HbA1c > 7% in patients whose FPG was < 130 mg/dl and correlation between HbA1c and plasma glucose at various times. The contribution of caloric intake, carbohydrate consumption and glycemic index of food to plasma glucose were determined.

Material and Method: Patients with type 2 diabetes, attended out-patient clinics at Siriraj Hospital, who had FPG of  < 130 mg/dl but HbA1c level of  > 7% were invited to participate in this 4-week study. They were treated with single or combined oral hypoglycemic agents except for alpha glucosidase inhibitors and glinide. Each patient performed self monitoring of capillary plasma glucose (CPG) before and 2 hours after each meal and before retiring to bed on the most convenient day in the first and fourth weeks and monitored two CPG before breakfast and before dinner weekly. Daily food intake was recorded in the logbooks.

Results: The observed patterns of CPG in 60 cases were postprandial hyperglycemia with FPG of < 130 mg/dl in 21.7%, a high pre-meal and post-meal CPG with FPG of < 130 mg/dl in 36.7% and elevated all fasting, pre-meal and post-meal CPG in 41.7% of the patients. The correlation coefficients between HbA1c at the end of the present study and CPG were 0.345, 0.40 and 0.337 at pre-breakfast, pre-lunch and pre-dinner, respectively (p = 0.01). The correlation coefficients between HbA1c and 2 hours CPG post-lunch, post-dinner and bed time were 0.402, 0.412 and 0.472, respectively (p = 0.01). The correlation between CPG and caloric intake, carbohydrate consumption or glycemic index of food were not observed.

Conclusion: Elevated blood glucose at all times was the commonest finding in type 2 diabetic patients whose FPG < 130 mg/dl but HbA1c level > 7%. A sole measurement of FPG should not be used to assure optimal glycemic control. Significant correlations between HbA1c and pre- or post- meal CPG indicated that frequent monitoring of pre- and post- meal could be used in assessing overall glycemic control.

Keywords: Fasting plasma glucose, Hemoglobin A1c, Postprandial hyperglycemia, Self monitoring of blood glucose