The glucose area under the profiles obtained with continuous glucose monitoring system relationships with HbA1c in pediatric type 1 diabetic patients

Abstract

OBJECTIVE - The purpose of this study was to determine whether the continuous glucose monitoring system (CGMS) (MiniMed, Sylmar, CA) 1) is sufficiently representative of the overall metabolic control as assessed by HbA1c, 2) could be used to identify a particular blood glucose threshold value affecting hemoglobin glycation; and 3) is able to show any relationship between particular glycemic profiles and HbA1c levels. RESEARCH DESIGN AND METHODS - Of 44 pediatric patients with type 1 diabetes who wore CGMS devices, 28 subjects were selected for the study. Criteria for inclusion were high levels of HbA1c (≥8%) for more than 1 year or a history of frequent hypoglycemic episodes and a complete CGMS registration for 72 h. Age of the subjects ranged from 5.7 to 24.8 years, the mean duration of disease was 7.63 ± 4.75 years, and the mean HbA1c value was 8.7 ± 1.3%. CGMS data were downloaded and glucose profiles were analyzed. The area under each glucose profile was calculated by means of a professional digital planimeter. RESULTS - The glucose profiles showed a high frequency of prolonged hyperglycemic periods (80% of subjects) and a low frequency of postmeal glycemic peaks (29% of subjects). Postlunch values were significantly correlated with HbA1c levels, but the correlation disappeared when controlling for glucose area values. Glucose area values significantly correlated with HbA1c levels both when considered as a whole (40-400 mg/dl; r = 0.53, P = 0.002) and when considered fractioned (40-150, 40-200, 40-250, 40-300 mg/dl), apart from the 40-90 mg/dl partial area. HbA1c levels were significantly decreased 3 and 6 months after use of CGMS (P = 0.05 and 0.03, respectively, paired Student's t test). CONCLUSIONS - HbA1c levels may be decreased by using the information obtained with the CGMS. Three-day glucose profiles are representative of the overall glucose control, because glucose area values correlate with HbA1c levels. The only glucose threshold below which there seems to be no correlation with HbA 1c is 90 mg/dl. Only glucose area, and not postprandial glucose values, are directly and independently correlated with HbA1c. Therefore, to improve metabolic control, it is necessary to lower the whole mean 24-h glycemia and not just the postprandial glucose values.