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

Abstract

Aims:

This study determined the test–retest reliability of a continuous glucose monitoring system (CGMS) (iPro™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 (SD_w, 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, CONGA₆, and CONGA₁₂. The remaining measures (i.e., SD_w, %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 SD_w, %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.