Bailey T. et al. Diabetes Technology Ther. 2015, 17(11), 1-8

ORIGINAL ARTICLE The Performance and Usability of a Factory-Calibrated Flash Glucose Monitoring System Timothy Bailey, MD, FACE, FACP,1 Bruce W. Bode, MD, FACE,2 Mark P. Christiansen, MD,3 Leslie J. Klaff, MD,4 and Shridhara Alva, PhD5 Abstract Introduction: The purpose of the study was to evaluate the performance and usability of the FreeStyleÒ LibreÔ Flash glucose monitoring system (Abbott Diabetes Care, Alameda, CA) for interstitial glucose results compared with capillary blood glucose results. Materials and Methods: Seventy-two study participants with type 1 or type 2 diabetes were enrolled by four U.S. clinical sites. A sensor was inserted on the back of each upper arm for up to 14 days. Three factory-only calibrated sensor lots were used in the study. Sensor glucose measurements were compared with capillary blood glucose (BG) results (approximately eight per day) obtained using the BG meter built into the reader (BG reference) and with the YSI analyzer (Yellow Springs Instrument, Yellow Springs, OH) reference tests at three clinic visits (32 samples per visit). Sensor readings were masked to the participants. Results: The accuracy of the results was demonstrated against capillary BG reference values, with 86.7% of sensor results within Consensus Error Grid Zone A. The percentage of readings within Consensus Error Grid Zone A on Days 2, 7, and 14 was 88.4%, 89.2%, and 85.2%, respectively. The overall mean absolute relative difference was 11.4%. The mean lag time between sensor and YSI reference values was 4.5 – 4.8 min. Sensor accuracy was not affected by factors such as body mass index, age, type of diabetes, clinical site, insulin administration, or hemoglobin A1c. Conclusions: Interstitial glucose measurements with the FreeStyle Libre system were found to be accurate compared with capillary BG reference values, with accuracy remaining stable over 14 days of wear and unaffected by patient characteristics. Introduction Capillary and venous blood glucose (BG) values are typically used as reference to evaluate the accuracy of in vivo sensor devices.1–5 Clinical laboratories use venous samples analyzed using a laboratory analyzer, whereas lay users use capillary BG measurements measured using a glu- cose meter for the calibration of sensors.6–8 Glucose con- centrations between the capillary and venous samples differ, and therefore the sample type used for calibration versus reference measurement may influence the results of an ac- curacy evaluation.9,10 The FreeStyleÒ LibreÔ Flash glucose monitoring system (Abbott Diabetes Care, Alameda, CA), hereafter referred to as the ‘‘System,’’ is an interstitial glucose monitoring system intended to be a replacement for the cap- illary BG measurement. Therefore, capillary BG may be considered an appropriate comparator in evaluating the per- formance and accuracy of this factory-only calibrated System. Additionally, capillary BG provides more reference points and represents real-life accuracy during daily patient use. 1 AMCR Institute, Escondido, California. 2 Atlanta Diabetes Associates, Atlanta, Georgia. 3 Diablo Clinical Research, Walnut Creek, California. 4 Rainier Clinical Research Center, Renton, Washington. 5 Clinical Affairs, Abbott Diabetes Care, Alameda, California. This study is registered with ClinicalTrials.gov with clinical trial registration number NCT02073058. ª The Author(s) 2015; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. DIABETES TECHNOLOGY & THERAPEUTICS Volume 17, Number 11, 2015 DOI: 10.1089/dia.2014.0378 1

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