Objective: Disparities were compared between flash glucose monitoring (FGM) sensor glucose (SG) and blood glucose (BG) values vs. between continuous glucose monitoring (CGM) SG and BG values to establish the accuracy of FGM SG values in patients with type 1 diabetes.

Methods: FGM (FreeStyle Libre Pro; Abbott Japan) and a sensor-augmented pump (SAP) with built-in CGM (MiniMed 620G; Medtronic Minimed) were simultaneously put in place in 8 outpatients with type 1 diabetes receiving SAP therapy (Age, 50.9 ± 6.3 years; BMI, 20.4±2.6 kg/m2; HbA1c, 7.4±0.3%; urinary C-peptide excretion, 1.5±0.7 µg/day; duration of SAP therapy, 11.9±3.7 months; insulin dose, 34.2±14.5 U/day). SMBG BG values at 385 points registered on Minimed 620G for calibration purposes and CGM/FGM SG values at the same time points, were selected to examine the accuracy of FGM SG values. Both these devices were evaluated for accuracy in terms of 1) simple correlation coefficients between CGM/FGM SG values and BG values; and 2) mean absolute relative differences (MARD) in SG values of CGM/FGM relative to BG values as reference.

Results: 1) A strong positive correlations were found between the CGM/FGM SG values and BG values (r = 0.984, p < 0.001 / r = 0.852, p< 0.001). 2) The MARD in CGM/FGM SG values were 5.81 ± 6.66% (0-39.4%) / 17.5 ± 24.8% (0-213.6%), and the frequency of MARD showing 10% or less accounted for 83% of all CGM SG values, and 48.3% of all FGM SG values. The relationship between the MARD of FGM SG values and the durations of FGM put in place varied depending on the number of days FGM put in place. Additionally, the disparity between the FGM SG values and the BG values varied greatly depending on the individual patient.

Conclusions: While FGM represents an innovative device for glucose monitoring, there is a wide disparity between the FGM SG and BG values in some patients with type 1 diabetes, suggesting that FGM may be appropriately positioned as an adjunct, but not an alternative, to SMBG.


M. Tanizawa: None. H. Takahashi: None. Y. Mori: None. K. Utsunomiya: None.

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