Accuracy of the SEVEN continuous glucose monitoring system: comparison with frequently sampled venous glucose measurements

Abstract

Background: The purpose of this study was to compare the accuracy of measurements obtained from the DexCom SEVEN system with Yellow Springs Instrument (YSI) laboratory measurements of venous blood glucose.

Methods: Seventy-two subjects with insulin-requiring diabetes, aged 18-71, were enrolled in a multicenter, prospective single-arm study. All participants wore the SEVEN continuous glucose monitoring (CGM) system for one, 7-day wear period. Calibration with capillary finger stick measurements was performed 2 hours after sensor insertion and once every 12 hours thereafter. A subset of subjects (28) wore two systems simultaneously to assess precision. All subjects participated in one, 10-hour in-clinic session on day 1, 4, or 7 of the study to compare CGM measurements against a laboratory method (YSI analyzer) using venous measurements taken once every 20 minutes. Carbohydrate consumption and insulin dosing were adjusted in order to obtain a broad range of glucose values.

Results: Comparison of CGM measurements with the laboratory reference method (n = 2318) gave mean and median absolute relative differences (ARDs) of 16.7 and 13.2%, respectively. The percentage was 70.4% in the clinically accurate Clarke error grid A zone and 27.5% in the benign error B zone. Performance of the SEVEN system was consistent over time with mean and median ARD lowest on day 7 as compared to YSI (13.3 and 10.2%, respectively). Average sensor time lag was 5 minutes.

Conclusions: Measurements of the DexCom SEVEN system were found to be consistent and accurate compared with venous measurements made using a laboratory reference method over 7 days of wear.

Figure 1.

Clark error grid plot of 7-day sensor (STS-7; DexCom, San Diego, CA) versus YSI. There are 70.4% of points in the clinically accurate A zone, 27.5% in the benign error B zone, and only 1.5% in the D zone and 0.04% in the E zone.

Figure 2.

Sample case. YSI on day 7: The subject was a 69-year-old man with a history of type 1 diabetes on continuous subcutaneous insulin infusion with a baseline HbA1c of 7.0% and a body mass index of 27.6 kg/m². Subject wore two sensors and had separate Ultra meters for calibration (CalMeter) and compara-tive (CompMeter) purposes. During the in-clinic day on day 7 of wear, reference YSI and CompMeter (Ultra) SMBG values were measured every 20 minutes, and a wide-range of glucose values was obtained by manipulating insulin dosing and carbohydrate ingestion. Note: for illustrative purposes, a good example of CGM tracking is shown; aver-age and poor examples are present in FDA-approved device labeling.