Assessing the Accuracy of Continuous Glucose Monitoring (CGM) Calibrated With Capillary Values Using Capillary or Venous Glucose Levels as a Reference

BACKGROUND

Using the standard venous reference for the evaluation of continuous glucose monitoring (CGM) systems could possibly negatively affect measured CGM accuracy since CGM are generally calibrated with capillary glucose and venous and capillary glucose concentrations differ. We therefore aimed to quantify the effect of using capillary versus venous glucose reference samples on estimated accuracy in capillary calibrated CGM.

METHODS

We evaluated 41 individuals with type 1 diabetes mellitus (T1DM) using the Dexcom G4 CGM system over 6 days. Patients calibrated their CGM devices with capillary glucose by means of the HemoCue system. During 2 visits, capillary and venous samples were simultaneously measured by HemoCue and compared to concomitantly obtained CGM readings. The mean absolute relative difference (MARD) was calculated using capillary and venous reference samples.

RESULTS

Venous glucose values were 0.83 mmol/L (15.0 mg/dl) lower than capillary values over all glycemic ranges, P < .0001. Below 4 mmol/l (72 mg/dl), the difference was 1.25 mmol/l (22.5 mg/dl), P = .0001, at 4-10 mmol/l (72-180 mg/dl), 0.67 mmol/l (12.0 mg/dl), P < .0001 and above 10 mmol/l (180 mg/dl), 0.95 mmol/l (17.1 mg/dl), P < .0001. MARD was 11.7% using capillary values as reference compared to 13.7% using venous samples, P = .037. Below 4 mmol/l (72 mg/dl) MARD was 16.6% and 31.8%, P = .048, at 4-10 mmol/l (72-180 mg/dl) 12.1% and 12.6%, P = .32, above 10 mmol/l (180 mg/dl) 8.7% and 9.2%, P = .82.

CONCLUSION

Using capillary glucose concentrations as reference to evaluate the accuracy of CGM calibrated with capillary samples is associated with a lower MARD than using venous glucose as the reference. Capillary glucose concentrations were significantly higher than venous in all glycemic ranges.

Predicting the effectiveness of insulin pump therapy on glycemic control in clinical practice: a retrospective study of patients with type 1 diabetes from 10 outpatient diabetes clinics in Sweden over 5 years

BACKGROUND

Multicenter long-term studies of predictors for the effectiveness of continuous subcutaneous insulin infusion (CSII) in clinical practice are lacking. We hypothesized that there are substantially greater reductions in hemoglobin A1c (HbA1c) in patients with poor glycemic control and that other predictors may also exist.

SUBJECTS AND METHODS

We used data from 10 outpatient diabetic clinics in Sweden and studied CSII treatment over 5 years. Patients with HbA1c values available ≤ 6 months before starting CSII and at 5 years were included (n = 272, 82% of CSII patients) along with 2,437 contemporaneous controls on multiple daily insulin injections (MDI). Baseline variables evaluated were age, sex, diabetes duration, insulin dose, body mass index (BMI), HbA1c at baseline, and outpatient clinical care unit.

RESULTS

At 5 years, significantly greater reductions in HbA1c by CSII compared with MDI were found for patients with higher baseline HbA1c (P = 0.032) and lower baseline BMI (P = 0.013). For baseline HbA1c levels of 7.0%, 8.0%, and 9.0% and a BMI of 25 kg/m(2), the reduction in HbA1c level by CSII was 0.08% (difference not significant), 0.16% (95% confidence interval, 0.03-0.29%), and 0.25% (95% confidence interval, 0.11-0.39%), respectively. Corresponding analyses for the change in HbA1c level from start to 1 and 2 years revealed a significant interaction of insulin pump therapy only with baseline HbA1c levels (P < 0.001 and P = 0.030, respectively). The interaction term between outpatient clinical care unit and CSII treatment was statistically significant for some care units, with some care units demonstrating a benefit from CSII and others demonstrating a detriment.

CONCLUSIONS

Patients with high HbA1c levels have a greater probability of improved HbA1c after initiating pump therapy, but effects remain relatively modest even for patients with poor control. Factors predicting successful insulin pump use need further study.

A clinical trial of the accuracy and treatment experience of the Dexcom G4 sensor (Dexcom G4 system) and Enlite sensor (guardian REAL-time system) tested simultaneously in ambulatory patients with type 1 diabetes

BACKGROUND

Continuous glucose monitoring (CGM) is a tool widely used in the treatment of patients with type 1 diabetes. The purpose of the current study was to evaluate whether accuracy and patient treatment satisfaction differ between the Enlite™ (Medtronic MiniMed, Inc., Northridge, CA) and Dexcom(®) (San Diego, CA) G4 PLATINUM CGM sensors.

SUBJECTS AND METHODS

Thirty-eight ambulatory patients with type 1 diabetes used the Dexcom G4 and Enlite sensors simultaneously for a minimum of 4 and maximum of 6 days. Patients measured capillary glucose levels with a HemoCue(®) (Ängelholm, Sweden) system six to 10 times a day. In addition, two inpatient studies were performed between Days 1-3 and 4-6.

RESULTS

The mean absolute relative difference (MARD) in blood glucose for the Dexcom G4 was significantly lower (13.9%) than for the Enlite sensor (17.8%) (P<0.0001). The corresponding MARDs for Days 1-3 were 15.0% versus 19.4% (P=0.0027) and 13.6% versus 15.9% (P=0.026) for Days 4-6. For glucose levels in the hypoglycemic range (<4.0 mmol/L), the MARD for the Dexcom G4 was 20.0% compared with 34.7% for the Enlite (P=0.0041). On a visual analog scale (VAS) (0-100), patients rated the Dexcom G4 more favorably than the Enlite in 12 out of the 13 user experience questions. For example, more patients rated their experience with the Dexcom G4 as positive (VAS, 79.7 vs. 46.6; P<0.0001) and preferred to use it in their daily lives (VAS, 79.1 vs. 42.1; P<0.0001).

CONCLUSIONS

The Dexcom G4 sensor was associated with greater overall accuracy than the Enlite sensor during initial (Days 1-3) and later (Days 4-6) use and for glucose levels in the hypoglycemic range. Patients reported a significantly more positive experience using the Dexcom G4 than the Enlite.