Differences Between Flash Glucose Monitor and Fingerprick Measurements.

Odd Staal,Sverre Christiansen,Øyvind Stavdahl,Anders Fougner,Sven Carlsen,Heidi Hansen

doi:10.3390/bios8040093

Abstract

Freestyle Libre (FL) is a factory calibrated Flash Glucose Monitor (FGM). We investigated Mean Absolute Relative Difference (MARD) between Self Monitoring of Blood Glucose (SMBG) and FL measurements in the first day of sensor wear in 39 subjects with Type 1 diabetes. The overall MARD was 12.3%, while the individual MARDs ranged from 4% to 25%. Five participants had a MARD ≥ 20%. We estimated bias and lag between the FL and SMBG measurements. The estimated biases range from −1.8 / to 1.4 /, and lags range from 2 to 24 . Bias is identified as a main cause of poor individual MARDs. The biases seem to persist in days 2–7 of sensor usage. All cases of MARD ≥ 20% in the first day are eliminated by bias correction, and overall MARD is reduced from 12.3% to 9.2%, indicating that adding support for voluntary user-supplied bias correction in the FL could improve its performance.

Highlights

People with diabetes need to control their blood glucose level to be as close as possible to the normal range, in order to avoid acute and chronic consequences of the disease
In this paper we investigate the accuracy of Freestyle Libre (FL) measurements compared to Self Monitoring of Blood Glucose (SMBG) measurements, and we investigate in detail the characteristics of the errors in the FL data, focusing on biases and lags in the FL glucose estimates
A Parkes/Consensus error grid (PEG) analysis found all measurements to be within zones A+B, with 81.7% in zone A

Summary

Introduction

People with diabetes need to control their blood glucose level to be as close as possible to the normal range, in order to avoid acute and chronic consequences of the disease. Continuous glucose monitoring (CGM) is an important tool for people with diabetes, primarily to detect potentially dangerous blood glucose levels and to assist in insulin bolusing. Due to the diffusion time of glucose from the capillaries to the subcutaneous interstitial fluid and diffusion across sensor membranes, CGM measurements are delayed compared to glucose measured in blood [2,3,4,5]. CGM systems have a disadvantage compared to direct blood glucose measurements, and lag is a known issue with present CGM systems that users need to be aware of

Methods

Discussion

Conclusion