Background: The Abbott FreeStyle Libre Flash glucose monitoring system (FGM) is one of the recently introduced personal continuous glucose monitoring systems. While FGM use has spread widely, few reports have examined the factors that determine its accuracy.

Methods: We performed oral glucose tolerance tests (OGTTs) in 25 Japanese subjects without diabetes.

Results: The mean absolute relative difference (MARD) in sensor glucose values of FGM (FGM-SG) with reference to self-monitoring of blood glucose (SMBG) levels was 10.9±4.1% during OGTTs. However, surprisingly, the MARD in FGM-SG with reference to plasma glucose (PG) levels was 20.3±10.3% during OGTTs, demonstrating the problems in accuracy of FGM-SG compared with that of PG levels in our study setting; however, this issue was not observed on comparison with accuracy of SMBG levels. Parkes error grid analyses showed that FGM-SG with either SMBG or PG levels as reference met the criteria of the International Organization for Standardization. Moreover, the MARD showed negative correlations with fasting blood sugar, homeostasis model assessment insulin resistance index, area under curve (AUC)-PG, and body mass index (BMI); multiple regression analyses revealed that BMI was the most contributing factor to the MARD between FGM-SG and PG levels. In other words, lean people showed more MARDs.

Conclusions: Inaccurate FGM data could potentially increase the risk of inappropriate treatment. Consideration of such factors might be critical while using FGM.


S. Yoshino: None. E. Yamada: None. S. Okada: None. T. Saito: None. M. Yamada: None.

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