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

The System has several features that distinguish it from existing sensor technology. The wired enzyme sensor is cali- brated in the factory and therefore requires no user calibration during 14 days of wear. This feature differs from existing sensors, which require multiple fingerstick BG measure- ments over the life of the sensor for calibration.11,12 The entire System’s on-body sensor patch worn on the back of the upper arm is disposable after use. The hand-held reader with the built-in FreeStyle Precision BG meter is used to scan the sensor to receive a glucose result along with historic results with a 15-min frequency for up to 8 h. The BG readings on the built-in meter are independent of, and do not influence, sensor readings. The System displays trends and alerts on the Reader but does not have real-time alarms, which may provide a good option for individuals who complain of alarm fatigue.11,13 The objective of this article is to describe the performance and usability of the System by comparing its scanned sensor results with capillary BG values measured using the built-in BG meter. Performance against the venous blood reference is provided for comparison. Materials and Methods This prospective, single-arm, clinical study was conducted at four U.S. clinical sites. The protocol and informed consent forms were approved by a central Institutional Review Board, and all subjects provided written informed consent before enrollment in the study. Study participants inserted and wore the sensor on the back of each upper arm (two sensors total), without any over- bandage, for up to 14 days. Three factory-calibrated pro- duction sensor lots were used for the study. This number is consistent with the industry practice to demonstrate the per- formance of reagent systems across multiple production lots. There were three scheduled in-clinic visits during the 14-day sensor wear period, where venous blood samples were collected every 15 min over an 8-h period for YSI analyzer (Yellow Springs Instrument, Yellow Springs, OH) reference tests. The first in-clinic visit was between Day 1 and 3, the second in-clinic visit was between Day 4 and 9, and the third in-clinic visit was between Day 10 and 14. Twenty-four (of 144) sensors that were dislodged prior to the second in-clinic visit were replaced; sensors that were dislodged after that time were not replaced. At least eight capillary BG tests, using the BG meter built into the reader, were required to be performed on each day of the sensor wear, both at home and in the clinic. One strip lot was used to minimize lot-to-lot variation. The preferred testing was upon waking, before each meal, an hour after each meal, and at bedtime. Immediately after each BG test, participants obtained a confirmation of a successful sensor scan. Sensor readings were masked to participants, who were asked to maintain their established diabetes management plan. There was no manipulation of the glucose levels of the subjects except for their normal meal and insulin doses. Cap- illary BG tests coincided with venous YSI samples drawn during in-clinic visits. A linear mixed model was used to assess sensitivity and mean absolute relative difference (MARD) between inser- tion sites, with subject as a random effect and insertion site (left arm, right arm) and lot as fixed effects. The lag between the System sensor and YSI reference was evaluated using a model that characterizes delay with a time constant.14 Analyses were carried out using SAS version 9.2 software (SAS Institute, Cary, NC). Results Seventy-two of 75 study participants were included in the evaluation. Three participants exited after Visit 1 (two could not comply with study visits, and one had non–study-related severe hypoglycemia prior to sensor insertion with unknown complications). The subject characteristics of the study par- ticipants are provided in Table 1. The real-time glucose level was available for 99.2% (25,834/26,045) of sensor scans, where complete sensor data were transferred to the reader. In total, 13,195 BG and 12,172 YSI reference results were paired with sensor glucose results. Twenty-eight pairs were excluded because the reference glucose result was beyond the BG system’s dynamic range (20–500 mg/dL), and 114 pairs were excluded because the sensor result was beyond the System’s dynamic range (40– 500 mg/dL). The percentages of results in Zone A of the Consensus and Clarke Error Grids were 86.7% and 85.5%, respectively (Fig. 1). The percentages of sensor results in Zones A and B of the Consensus and Clarke Error Grids were 99.7% and 99.0%, respectively, whereas 86.2% and 82.8% of sensor results were within – 15 mg/dL or – 20% of BG ref- erence and venous reference, respectively. Continuous glu- cose error grid analysis (EGA) versus venous reference showed 96.5% (11,232/11,640) of the data categorized as clinically accurate, and a further 2.4% (274/11,640) were classified as benign errors. The overall MARD was 11.4% for sensor results with capillary BG reference. The overall MARD in the clinic alone for sensors’ results with capillary BG reference and with YSI reference was 12.1% and 12%, respectively. A detailed dif- ference analysis against capillary and venous blood reference Table 1. Baseline Characteristics of Study Participants Characteristic Mean – SD Median Range Age (years) 46.4 – 15.1 48.5 18–71 Weight Pounds 182.2 – 42.1 175.8 102.0–299.8 Kilograms 82.6 – 19.1 79.7 46.3–136.0 Height Inches 67.1 – 4.3 66.5 59–81 Meters 1.70 – 0.11 1.69 1.50–2.06 Body mass index (kg/m2 ) 28.3 – 5.3 27.4 18.7–47.2 Years since diagnosis 23.0 – 13.1 22.3 2.4–50.6 Total number of injections per day (n = 33 subjects) 4.6 – 1.1 4 3–8 HbA1c (%) 7.8 – 1.2 7.8 5.5–11.5 Number of BG tests per day 7.4 – 1.0 7.7 4.0–9.6 Hemoglobin A1c (HbA1c) levels were measured at the start of the study. The number of tests per day was calculated from the test records on the FreeStyle Libre Reader. BG, blood glucose. 2 BAILEY ET AL. Age (years) 46.4 – 15.148.518–71 Pounds 182.2 – 42.1175.8102.0–299.8 Kilograms 82.6 – 19.179.746.3–136.0 Inches 67.1 – 4.366.559–81 Meters 1.70 – 0.111.691.50–2.06 ) 28.3 – 5.327.418.7–47.2 Years since diagnosis 23.0 – 13.122.32.4–50.6 4.6 – 1.143–8 HbA1c (%) 7.8 – 1.27.85.5–11.5 7.4 – 1.07.74.0–9.6

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