Accuracy of a Factory Calibrated Retrospective CGM Device and the Comparison to a Conventionally Calibrated Retrospective CGM Device: A Pilot Study

Abstract

Objective: This study aimed to examine the accuracy of FreeStyle Libre Pro, a factory calibrated retrospective continuous glucose monitoring (CGM) device, and compare its measurements to those by iPro2, a conventionally calibrated retrospective CGM device. Methods: FreeStyle Libre Pro and iPro2 were simultaneously used in 15 patients with type 2 diabetes mellitus. As these devices have different sensor duration, data from the initial 168 hours period were used. Finger prick glucose tests were performed using a conventional glucose meter, OneTouch UltraVue. The mean absolute relative difference (MARD) and mean absolute difference (MAD) of FreeStyle Libre Pro compared to conventional finger prick blood glucose tests were calculated. Furthermore, the paired glucose measurements obtained by FreeStyle Libre Pro and iPro2 were compared. Results: Overall MARD of FreeStyle Libre Pro was 17.4%, and, when limited to range ≥ 100 mg/dl, MARD was 16.8%. Overall MAD of FreeStyle Libre Pro was 32.0 mg/dl, and, when limited to range < 100 mg/dl, MAD was 21.1 mg/dl. Mean glucose measurements obtained by FreeStyle Libre Pro were significantly lower than those obtained by iPro2 (151.3±60.4 mg/dl vs. 179.4±64.1 mg/dl, P < 0.01). Linear regression analysis revealed significant correlation between glucose measurements obtained by FreeStyle Libre Pro and those obtained by iPro2: Glucose (FreeStyle Libre Pro) (mg/dl) = 0.86 × Glucose (iPro2) - 3.31 (mg/dl), r = 0.914, P < 0.01. Conclusions: FreeStyle Libre Pro is convenient to use because it does not need calibration by finger prick glucose tests, however our results supports the importance of confirming the measurements of FreeStyle Libre Pro by conventional finger prick glucose tests or central laboratory tests.