Accuracy of two continuous glucose monitoring systems: a head-to-head comparison under clinical research centre and daily life conditions

Abstract

Aims: To assess the accuracy and reliability of the two most widely used continuous glucose monitoring (CGM) systems.

Methods: We studied the Dexcom®G4 Platinum (DG4P; Dexcom, San Diego, CA, USA) and Medtronic Paradigm Veo Enlite system (ENL; Medtronic, Northridge, CA, USA) CGM systems, in 24 patients with type 1 diabetes. The CGM systems were tested during 6-day home use and a nested 6-h clinical research centre (CRC) visit. During the CRC visit, frequent venous blood glucose samples were used as reference while patients received a meal with an increased insulin bolus to induce an aggravated postprandial glucose nadir. At home, patients performed at least six reference capillary blood measurements per day. A Wilcoxon signed-rank test was performed using all data points ≥15 min apart.

Results: The overall mean absolute relative difference (MARD) value [standard deviation (s.d.)] measured at the CRC was 13.6 (11.0)% for the DG4P and 16.6 (13.5)% for the ENL [p < 0.0002, confidence interval of difference (CI Δ) 1.7-4.3%, n = 530]. The overall MARD assessed at home was 12.2 (12.0)% for the DG4P and 19.9 (20.5)% for the ENL (p < 0.0001, CI Δ = 5.8-8.7%, n = 839). During the CRC visit, the MARD in the hypoglycaemic range [≤3.9 mmol/l (70 mg/dl)], was 17.6 (12.2)% for the DG4P and 24.6 (18.8)% for the ENL (p = 0.005, CI Δ 3.1-10.7%, n = 117). Both sensors showed higher MARD values during hypoglycaemia than during euglycaemia [3.9-10 mmol/l (70-180 mg/dl)]: for the DG4P 17.6 versus 13.0% and for the ENL 24.6 versus 14.2%.

Conclusions: During circumstances of intended use, including both a CRC and home phase, the ENL was noticeably less accurate than the DG4P sensor. Both sensors showed lower accuracy in the hypoglycaemic range. The DG4P was less affected by this negative effect of hypoglycaemia on sensor accuracy than was the ENL.

Trial registration: ClinicalTrials.gov NCT01751932.

Keywords: CSII; type 1 diabetes.

© 2014 The Authors. Diabetes, Obesity and Metabolism published by John Wiley & Sons Ltd.

Figures

Figure 1

Bland–Altman plots for the Dexcom®G4 Platinum (DG4P) and Medtronic Paradigm Veo Enlite system (ENL). Panel A: clinical research centre (CRC) phase and panel B: home phase. The x-axis represents the average reference and continuous glucose monitoring (CGM) glucose measurements, the y-axis represents the difference (CGM – reference) versus the average of values measured by CGM expressed as a percentage. The long dashed line is drawn at the mean difference; dotted lines are drawn at the mean difference ± 1.96 times the standard deviation of the mean difference.

Figure 2

Clarke error grid analysis combined for the Dexcom®G4 Platinum (DG4P; grey dots) and the Medtronic Paradigm Veo Enlite (ENL; black dots) during the clinical research centre (CRC) phase (A) and the home phase (B). CRC phase: based on a total of 532 DG4P – YSI pairs, the DG4P had 79.9% of values in zone A, 15.0% in zone B, 0% in zone C, 5.1% in zone D and 0% in zone E. Based on a total of 530 ENL–YSI (reference value measured with the YSI blood glucose analyser) pairs, the ENL had 72.3% of values in zone A, 20.0% in zone B, 0% in zone C, 7.7% in zone D and 0% in zone E. Home phase: based on a total of 987 DG4P – self-monitoring of blood glucose (SMBG) pairs, the DG4P had 83.0% of values in zone A, 15.0% in zone B, 0.3% in zone C, 1.6% in zone D and 0.1% in zone E. Based on a total of 839 ENL – SMBG pairs, the ENL had 64.6% of values in zone A, 29.8% in zone B, 1.6% in zone C, 3.6% in zone D and 0.5% in zone E.

Figure 3

(A) Cumulative distribution of individual continuous glucose monitoring (CGM) performance (in the clinical research centre). (B) Cumulative distribution of individual CGM performance (at home). DG4P, Dexcom®G4 Platinum system; ENL, Medtronic Paradigm Veo Enlite system; MARD, mean absolute relative difference.

Figure 4

Average continuous glucose monitoring accuracy per day (mean absolute relative difference (MARD) ± 95% confidence interval) for the Dexcom®G4 Platinum (DG4P) and the Medtronic Paradigm Veo Enlite (ENL) systems.