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Pediatr Diabetes. 2019 Aug;20(5):604-612. doi: 10.1111/pedi.12854. Epub 2019 Apr 17.

Discrepancies between methods of continuous glucose monitoring in key metrics of glucose control in children with type 1 diabetes.

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Department of Pediatrics, Diabetology, Endocrinology and Nephrology, Medical University of Lodz, Lodz, Poland.
Department of Biostatistics and Translational Medicine, Medical University of Lodz, Lodz, Poland.
Postgraduate School of Molecular Medicine, Warsaw, Poland.
Department of Pediatrics, Oncology and Hematology, Medical, University of Lodz, Lodz, Poland.
Department of Radiation Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.



We aimed to compare glycemic control and variability parameters obtained from paired records of real-time continuous glucose monitoring (RT-CGM) and flash glucose monitoring (FGM).


Ten Polish boys and 11 girls aged 15.3 ± 2.1 years with type 1 diabetes for 7.7 ± 4.5 years and glycated hemoglobin 7.35 ± 0.7% (57 ± 5 mmol/mol) were recruited between August 2017 and June 2018 and equipped with devices for RT-CGM (iPro2 system with Enlite electrodes) and FGM (FreeStyle Libre) for 1 week. Afterwards, Glyculator 2.0 software was used to calculate and compare key metrics of glycemic control listed in the International Consensus on Use of Continuous Glucose Monitoring, with distinction into all record/night-time/day-time blocks when appropriate.


Agreement between the two systems' measurements across patients ranged from poor (R2  = .39) to nearly perfect (R2  = .97). Significant differences between RT-CGM and FGM were observed in five important metrics: coefficient of variation (median difference: -4.12% [25%-75%: -7.50% to -2.96%], P = .0001), low blood glucose index (-0.88 [-1.88 to -0.18], P = .0004), % of time below 70 mg/dL (3.9 mmol/L) (-4.77 [-8.39 to -1.19], P = .0015) and 54 mg/dL (3 mmol/L) (-1.33 [-4.07 to 0.00], P = .0033) and primary time in range (TIR) 70-180 mg/dL (8.58 [1.31 to 12.66], P = .0006).


RT-CGM and FGM differ in their estimates of clinically important indices of glycemic control. Therefore, such metrics cannot be directly compared between people using different systems. Our result necessitates system-specific guidelines and targets if TIR and glycemic variability are to be used as an endpoint in clinical trials.


continuous glucose monitoring; flash glucose monitoring; glycemic variability; type 1 diabetes


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