Test-Retest Reliability of a Continuous Glucose Monitoring System in Individuals with Type 2 Diabetes

Aims: This study determined the test-retest reliability of a continuous glucose monitoring system (CGMS) (iPro (TM) 2; Medtronic, Northridge, CA) under standardized conditions in individuals with type 2 diabetes (T2D). Subjects and Methods: Fourteen individuals with T2D spent two nonconsecutive days in a calorimetry unit. On both days, meals, medication, and exercise were standardized. Glucose concentrations were measured continuously by CGMS, from which daily mean glucose concentration (GLU(mean)), time spent in hyperglycemia (t (> 10.0 mmol/L)), and meal, exercise, and nocturnal mean glucose concentrations, as well as glycemic variability (SDw, percentage coefficient of variation [%cv(w)], mean amplitude of glycemic excursions [MAGE(c), MAGE(ave), and MAGE(abs.gos)], and continuous overlapping net glycemic action [CONGA(n)]) were estimated. Absolute and relative reliabilities were investigated using coefficient of variation (CV) and intraclass correlation, respectively. Results: Relative reliability ranged from 0.77 to 0.95 (P < 0.05) for GLU(mean) and meal, exercise, and nocturnal glycemia with CV ranging from 3.9% to 11.7%. Despite significant relative reliability (R=0.93; P < 0.01), t (> 10.0 mmol/L) showed larger CV (54.7%). Among the different glycemic variability measures, a significant between-day difference was observed in MAGE(c), MAGE(ave), CONGA(6), and CONGA(12). The remaining measures (i.e., SDw, %cv(w), MAGE(abs.gos), and CONGA(1-4)) indicated no between-day differences and significant relative reliability. Conclusions: In individuals with T2D, CGMS-estimated glycemic profiles were characterized by high relative and absolute reliability for both daily and shorter-term measurements as represented by GLU(mean) and meal, exercise, and nocturnal glycemia. Among the different methods to calculate glycemic variability, our results showed SDw, %cv(w), MAGE(abs.gos), and CONGA(n) with n <= 4 were reliable measures. These results suggest the usefulness of CGMS in clinical trials utilizing repeated measured.