Page 158 - Glucose Monitoring Devices

CHAPTER

8
Accuracy of CGM systems

1
William L. Clarke, MD , Boris Kovatchev, PhD 2
1
Profesor, Emeritus of Pediatric Endocrinology, Department of Pediatrics, University of Virginia,
2
Charlottesville, VA, United States; Professor and Director, Center for Diabetes Technology,
Department of Psychiatry and Neurobehavioral Sciences, University of Virginia, Charlottesville,
Virginia, United States

Introduction

Continuous glucose monitoring (CGM) was introduced into the management op-
tions available for assisting patients with diabetes in controlling their disease nearly
20 years ago [1e3]. The advent of this technology has led to remarkable changes in
day-to-day living and the possibility of long-term reduction in the risk of serious
complications. Since then, significant progress has been made toward versatile
and reliable CGM devices that not only monitor the entire course of blood glucose
(BG) day and night but also provide feedback to the patient, such as alarms when BG
reaches preset low or high levels. A number of early studies have documented the
benefits of CGM and charted guidelines for its clinical use [4e9]. Perhaps most
importantly, CGM has provided a missing critical piece needed for the development
of automated closed-loop control, known as the “artificial pancreas” [10e14]. With
CGM systems, patients can immediately confirm their symptoms of elevated or low
BG levels and determine the direction of their BG trends and the rate of BG change.
With real-time CGM, alarms for low and high BG have made it possible for patients
and their families to sleep throughout the night.
However, while CGM has the potential to revolutionize the control of diabetes,
it also generates data streams that are both voluminous and complex. The utiliza-
tion of such data requires an understanding of the physical, biochemical, and math-
ematical principles and properties involved in this new technology. It is important
to know that CGM devices measure glucose concentration in a different
compartmentdthe interstitium. Interstitial glucose (IG) fluctuations are related
to BG presumably via the diffusion process [15e17]. Historically, to account for
the gradient between BG and IG, CGM devices have been calibrated with capillary
glucose; more recently, factory calibration is used to bring the typically lower IG
concentration to BG levels. Successful calibration would adjust the amplitude of
IG fluctuations with respect to BG but would not eliminate the possible time lag
due to BG-to-IG glucose transport. Because such a time lag could greatly influence
the accuracy of CGM, a number of studies have been dedicated to its investigation,

Glucose Monitoring Devices. https://doi.org/10.1016/B978-0-12-816714-4.00008-9 159
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