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 HbA(1c), 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 HbA(1c) 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 HbA(1c) (> or =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 HbA(1c) 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 HbA(1c) levels, but the correlation disappeared when controlling for glucose area values. Glucose area values significantly correlated with HbA(1c) 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. HbA(1c) 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: HbA(1c) 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 HbA(1c) 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 HbA(1c). Therefore, to improve metabolic control, it is necessary to lower the whole mean 24-h glycemia and not just the postprandial glucose values.