Accuracy of a Professional Continuous Glucose Monitoring Device in Individuals with Type 2 Diabetes Mellitus

Among continuous glucose monitoring (CGM) devices, which continuously measure glucose concentration in subcutaneous interstitial fluid for comprehensive monitoring of blood glucose profile, only FreeStyle Libre Pro® (Abbott Diabetes Care) is currently available in Japan as a professional system. FreeStyle Libre Pro® is easy to use because it does not require calibration by self-monitoring of blood glucose (SMBG), but information on its accuracy has been insufficient. To evaluate the measurement accuracy of FreeStyle Libre Pro®, we have now compared blood glucose levels determined by this device with those measured by SMBG in 40 individuals with type 2 diabetes mellitus. The mean absolute relative difference (MARD) for FreeStyle Libre Pro® measurements compared with SMBG measurements was calculated as an index of CGM accuracy. Overall blood glucose values measured by SMBG were 167.0 ± 60.1 mg/dL, and those determined by FreeStyle Libre Pro® were 155.0 ± 60.7 mg/dL, with this difference being statistically significant. The MARD for FreeStyle Libre Pro® relative to SMBG was 12.7 ± 9.3%. It was substantially higher in 2 of the 40 patients, at 49.2% and 47.5%, than in the other 38 individuals. MARD values did not differ significantly between before and 2 h after meals. However, the MARD was significantly higher for SMBG values of <100 mg/dL than for those of ≥250 mg/dL. Our results thus indicate that the measurement accuracy of FreeStyle Libre Pro® is relatively good, but that some cases in which values determined by the device deviate from SMBG values require caution in interpretation.