Clinical Aspects of Continuous Glucose Monitoring

Nina Verheyen, Jens Gios, Christophe De Block
European Endocrinology, 2010;6(2):26-30

Abstract

Abstract
In patients with diabetes, strict glycaemic control is warranted to achieve an improvement in metabolic outcome. When performing self-monitoring of blood glucose, hypo- and hyperglycaemic excursions can be missed. Continuous glucose monitoring (CGM) provides a complete picture of the patient’s glucose levels throughout the day. CGM may also warn against impending glycaemic excursions, thereby reducing the fear of hypoglycaemia and improving the patient’s quality of life. Patients with brittle diabetes, hypoglycaemia unawareness or gastroparesis, pregnant women with diabetes and those who are critically ill may particularly benefit from CGM. Patients and care-givers must be highly motivated, technologically adept and aware of the limitations of CGM devices to successfully use this type of monitoring in daily practice. The impact of CGM on metabolic control, incidence of hypoglycaemia, chronic complications and quality of life needs further investigation.

Keywords
Continuous glucose monitoring (CGM), diabetes, metabolic control

Disclosure: The authors have no conflicts of interest to declare.
Received: 1 June 2009 Accepted: 9 November 2009 Citation: European Endocrinology, 2010;6(2):26–30
Correspondence: Christophe De Block, Department of Endocrinology–Diabetology, Antwerp University Hospital, Wilrijkstraat 10, B-2650 Edegem, Belgium. E: christophe.deblock@ua.ac.be

Citation European Endocrinology, 2010;6(2):26-30
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More than 15 years have elapsed since the publication of major studies that clearly demonstrated the benefit of aggressive glycaemic control in persons with diabetes.1–3 Currently, frequent self-monitoring of blood glucose (SMBG) is required to achieve tight glycaemic control.4 However, SMBG does not provide information about the direction, magnitude, duration, frequency and causes of fluctuations in blood glucose values. Moreover, the fear of hypoglycaemia has a significant impact on patient quality of life and therefore remains a major barrier to achieving optimal glycaemic control. Whereas SMBG takes only a snapshot, continuous glucose monitoring (CGM) provides a complete motion picture of glucose values throughout the day.5–7 In this way CGM, may prove to be an important asset in future diabetes care. This review addresses advantages and limitations of CGM and the target population.

Advantages of Continuous Glucose Monitoring

Metabolic Control

CGM systems provide the patient and the treating physician with a complete picture of glucose levels throughout the day. They can be used either as a Holter system (retrospectively) or as a realtime monitor.5–8 CGM readings may facilitate the making of specific therapeutic adjustments to improve metabolic control. These adjustments can be based either on retrospective analysis and pattern recognition or on realtime data verified by SMBG. It will also be possible to take preventative measures by warning the patient against impending hypo- and hyperglycaemic excursions.8,9

A number of non-randomised, uncontrolled trials have documented improvement of glycated haemoglobin (HbA1c ) and glycaemic excursions (see Table 1).10–19 A total of 13 randomised controlled trials (RCTs) of CGM on metabolic control have been published to date (see Table 1).20–32 In 12 RCTs, HbA1c was used as the primary end-point. Seven RCTs used CGM in retrospect and only one study showed improvement in HbA1c compared with standard SMBG monitoring.23 Five RCTs used realtime CGM, making dynamic adjustments in insulin therapy based on realtime CGM data and verifying measurements with SMBG. All showed improvement of HbA1c levels compared with standard SMBG, except one.25 Realtime CGM reduced glycaemic variability and decreased the time spent in hypo- and hyperglycaemia.21,27,28,31

Recently, the results of the RCT sponsored by the Juvenile Diabetes Research Foundation (JDRF) were published.32 In this multicentre clinical trial, 322 adults, adolescents and children with type 1 diabetes who were already receiving intensive insulin therapy were randomly assigned to a group with realtime CGM or to a control group performing SMBG. This study showed a significant between-group difference in the change in HbA1c from baseline to week 26 in patients who were 25 years of age or older, favouring the CGM group (-0.71 versus -0.35%).32In addition, more patients in the CGM group had a relative reduction of 10% or more in mean HbA1c levels and a higher number achieved the target HbA1c level of <7.0%. The percentage of time per day within the target glucose range of 70–180mg/dl was significantly greater in the CGM group. Among patients who were 15–24 years of age, no significant differences in any of the glycaemic measures were observed between groups.32 However, only 30% of these patients used CGM on six or more days per week compared with 83% in patients 25 years of age or older. Among patients who were eight to 14 years of age, the mean decrease in HbA1c levels was 0.38% in the CGM group, which did not differ significantly from the control group. However, secondary indices of glycaemic control were improved in the CGM group, with more patients having a relative reduction of 10% or more in HbA1c levels and more achieving the target HbA1c level of <7.0%.32

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