Identifying appropriate patients for continuous glucose monitoring (CGM) use is a vital component of therapy success. Potential candidates come from a diverse group of individuals with diabetes.

Many people with type 1 diabetes may be excellent candidates for CGM therapy. Studies of the Juvenile Diabetes Research Foundation (JDRF) showed improvement in A1C levels in children, adolescents, and adults with type 1 diabetes with the use of three different CGM systems (1,2). However, the improvement in glycemic control was significant only in the adult agegroup because of relatively poor sustained adherence to CGM therapy in children and adolescents. With improved adherence, all groups showed improved A1C. Benefits were also greater for people with higher baseline A1C levels. A recent re-analysis of JDRF study data showed statistically significant improvements in the important measures of time spent in hypoglycemia, hyperglycemia, and glycemic variability (3). People with type 1 diabetes on either continuous subcutaneous insulin infusion (CSII) or multiple daily injection (MDI) therapy have been shown to benefit from CGM therapy (46).

People with type 2 diabetes, particularly those using insulin, also may be candidates for CGM. In 2017, the U.S. Centers for Medicare & Medicaid Services (CMS) began covering the Dexcom G5 Mobile system for people with type 1 or type 2 diabetes on intensive insulin therapy, defined as three or more daily injections of insulin or CSII therapy. A recent trial involving 158 people with type 2 diabetes on MDI insulin therapy randomized patients to usual care versus Dexcom G4 Platinum CGM-guided therapy. After 6 months, mean A1C levels improved from 8.5 to 7.7% in the CGM-treated group versus 8.0% in the usual care group (P = 0.022) (7). CMS also covers the FreeStyle Libre (Abbott, Alameda, CA) flash CGM (FCGM) system in the same populations. Use of FCGM for 6 months in people with type 2 diabetes on intensive insulin therapy resulted in statistically significant reductions in rates of hypoglycemia below blood glucose levels of 70, 55, and 45 mg/dL by 55, 68, and 75%, respectively (8). People using FCGM also reduced test strip use by 90% and scanned the CGM sensor an average of 8.3 times per day.

Pregnant women with diabetes are strong candidates for CGM. The American Diabetes Association recommends an A1C target of <6% during pregnancy for women with preexisting type 1 or type 2 diabetes if this goal can be achieved without excessive hypoglycemia (9), an oftendifficult accomplishment. Studies have demonstrated improvement in neonatal outcomes and significantly more time spent in target range during pregnancy with the use of CGM therapy (10,11). Women with gestational diabetes mellitus (GDM) may benefit from CGM use as well. In a study of 340 Chinese women with GDM randomized to intermittent prospective CGM use versus SMBG testing seven times per day throughout pregnancy, those using CGM showed superior glycemic variability, had infants with a lower mean birth weight, and had a lower risk of preeclampsia and a lower rate of cesarean delivery (12).

Another group of people who are excellent candidates for CGM therapy are those with hypoglycemia unawareness or a significant fear of hypoglycemia. Hypoglycemia unawareness increases the risk of severe hypoglycemia sixfold in patients with type 1 diabetes and ninefold in patients with type 2 diabetes (13,14). The IMPACT study using the FreeStyle Libre system in 239 people with type 1 diabetes for 6 months demonstrated reductions of 40% in nocturnal hypoglycemia, 50% in serious hypoglycemia (<55 mg/dL), and 91% in routine fingerstick blood glucose measurements (15). A retrospective study of 35 people with type 1 diabetes and established hypoglycemia unawareness showed a significant reduction in episodes of severe hypoglycemia from a mean rate of 8.1 to 0.6 episodes/patient-year (P = 0.005) over 1 year with multiple CGM systems (16). A subsequent retrospective study demonstrated an 86% reduction in risk for severe hypoglycemia requiring medical assistance in the first year of real-time CGM therapy (P = 0.0013) in people with type 1 diabetes who reported wearing their CGM system on an “almost daily” basis (17). There was also a strong trend toward a reduction in fear of hypoglycemia. More recently, a significant reduction in fear of hypoglycemia was shown in 20 people with type 1 diabetes after only 8 weeks of real-time CGM therapy (P = 0.01) (18).

It is important not to assess a person’s eligibility for CGM based on superficial observation. In particular, those with dexterity problems or visual disability may be appropriate candidates for CGM therapy, as evidenced by a case report of a person with type 1 diabetes, complete blindness, frequent hypoglycemia, and hypoglycemia unawareness who was able to rapidly and dramatically improve glycemic control with real-time CGM by learning to respond more appropriately to high and low blood glucose alerts (19). This patient’s average blood glucose decreased from 162 mg/dL during the first 4 days of CGM use to 138 mg/dL during the next 4 days, and there was also improvement in glycemic variability. The percentage of time spent in the high glucose range (>180 mg/dL) improved from 35 to 18%, and the percentage of time spent in the low glucose range (<80 mg/dL) improved from 9 to 3% with no episodes of severe hypoglycemia. People with dexterity or visual loss may need the help of a family member or caregiver to assist with CGM sensor insertion and calibrations.

Obviously, there are individuals for whom CGM therapy may not be beneficial or appropriate. It is important for people with diabetes to understand the strengths and limitations of CGM systems as related to their individual needs. (See the article on p. 8 of this compendium for a description of available systems.) Some people have misconceptions about CGM therapy, believing incorrectly, for example, that they may never have to perform fingerstick blood glucose testing for systems requiring calibration, that the CGM system is going to automatically adjust all aspects of CSII therapy, or that they may be able to take a completely hands-off approach to managing their diabetes. Others experience emotional distress due to “information overload” from the amount of data available through CGM. Also, people with type 2 diabetes who are stable on oral medications have not been shown to benefit from CGM. Appropriately selected individuals will have the best chance of improving their glucose control and outcomes when they consult the device frequently and are taught to use continuous data to make informed and timely treatment decisions.

The opinions expressed are those of the authors and do not necessarily reflect those of Abbott Diabetes Care or the American Diabetes Association. The content was developed by the authors and does not represent the policy or position of the American Diabetes Association, any of its boards or committees, or any of its journals or their editors or editorial boards.

Dualities of Interest

I.B.H. has served as a consultant to Abbott Diabetes Care, Adocia, Bigfoot, and Roche. His institution has received research grant support from Medtronic.

T.B. has served on advisory boards of Bayer Health Care, Boehringer Ingelheim, DreaMed Diabetes, Eli Lilly, Medtronic, Novo Nordisk, and Sanofi. His institution has received research grant support, with receipt of travel and accommodation expenses in some cases, from Abbott Diabetes Care, Diamyd, GluSense, Medtronic, Novo Nordisk, Sandoz, and Sanofi. He has received honoraria for participating on the speakers bureaus of Bayer Health Care, Eli Lilly, Medtronic, Novo Nordisk, Roche, and Sanofi. He owns stock in DreaMed Diabetes.

A.L.P. has served on advisory boards for Abbott Diabetes Care, Becton Dickinson, Bigfoot, Boehringer Ingelheim, Eli Lilly, Lexicon, Livongo, Medscape, Merck, Novo Nordisk, OptumHealth, Sanofi, and Science 37. She has received research grant support from Dexcom and Mannkind. She participates on a speakers bureau for Novo Nordisk.J.J.C. participates in speakers bureaus for Janssen, Merck, Novo Nordisk, and Sanofi.

G.A. has served as a consultant and on a steering committee for Dexcom and on an advisory board for Novo Nordisk, and her institution has received research grant support from AstraZeneca and Novo Nordisk.

R.M.B.’s institution has received payment for his services as a research investigator, consultant, or advisory board member for Abbott Diabetes Care, Becton Dickinson, Boehringer Ingelheim, Bristol-Myers Squibb/AstraZeneca, Dexcom, Eli Lilly, Hygieia, Johnson & Johnson, Medtronic, Merck, Novo Nordisk, Roche, Sanofi, and Takeda. R.M.B. has inherited Merck stock, volunteers for the American Diabetes Association and JDRF, and receives funding from the National Institutes of Health for diabetes technology research.

Acknowledgments

Writing support services for this compendium were provided by Carol Verderese of The Diabetes Education Group in Lakeville, CT. Editorial and project management services were provided by Debbie Kendall of Kendall Editorial in Richmond, VA.

Author Contributions

All authors researched and wrote their respective section(s). Lead author I.B.H. reviewed all content and is the guarantor of this work.

1.
Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group
.
Continuous glucose monitoring and intensive treatment of type 1 diabetes
.
N Engl J Med
2008
;
359
:
1464
1476
2.
Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group
.
Effectiveness of continuous glucose monitoring in a clinical care environment: evidence from the Juvenile Diabetes Research Foundation Continuous Glucose Monitoring (JDRF-CGM) trial
.
Diabetes Care
2010
;
33
:
17
22
3.
El-Laboudi
AH
,
Godsland
IF
,
Johnston
DG
,
Oliver
NS
.
Measures of glycemic variability in type 1 diabetes and the effect of real-time continuous glucose monitoring
.
Diabetes Technol Ther
2016
;
18
:
806
812
4.
Foster
NC
,
Miller
KM
,
Tamborlane
WV
,
Bergenstal
RM
,
Beck
RW
;
T1D Exchange Clinic Network
.
Continuous glucose monitoring in patients with type 1 diabetes using insulin injections
.
Diabetes Care
2016
;
39
:
e81
e82
5.
Lind
M
,
Polonsky
W
,
Hirsch
IB
, et al
Design and methods of a randomized trial of continuous glucose monitoring in persons with type 1 diabetes with impaired glycemic control treated with multiple daily insulin injections (GOLD study)
.
J Diabetes Sci Technol
2016
;
10
:
754
761
6.
Miller
K
,
Foster
N
,
Tamborlane
W
,
Bergenstal
R
,
Beck
R
.
Continuous glucose monitoring in T1D patients using injections of insulin: a report from the T1D Exchange clinic registry [Abstract 069]
.
Diabetes Technol Ther
2016
;
18
:
A–27
7.
Beck
RW
,
Riddlesworth
TD
,
Ruedy
K
, et al;
DIAMOND Study Group
.
Continuous glucose monitoring versus usual care in patients with type 2 diabetes receiving multiple daily insulin injections: a randomized trial
.
Ann Intern Med
2017
;
167
:
365
374
8.
Haak
T
,
Hanaire
H
,
Ajjan
R
,
Hermanns
N
,
Riveline
JP
,
Rayman
G
.
Flash glucose-sensing technology as a replacement for blood glucose monitoring for the management of insulin-treated type 2 diabetes: a multicenter, open-label randomized controlled trial
.
Diabetes Ther
2017
;
8
:
55
73
9.
American Diabetes Association
.
Management of diabetes in pregnancy. Sec. 13 in Standards of Medical Care in Diabetes—2018
.
Diabetes Care
2018
;
41
(
Suppl. 1
):
S137
S143
10.
Murphy
HR
,
Rayman
G
,
Lewis
K
, et al
Effectiveness of continuous glucose monitoring in pregnant women with diabetes: randomized clinical trial
.
BMJ
2008
;
337
:
a1680
11.
Feig
DS
,
Donovan
LE
,
Corcoy
R
, et al;
CONCEPTT Collaborative Group
.
Continuous glucose monitoring in pregnant women with type 1 diabetes (CONCEPTT): a multicenter international randomized controlled trial
.
Lancet
2017
;
390
:
2347
2359
12.
Yu
F
,
Lv
L
,
Liang
Z
, et al
Continuous glucose monitoring effects on maternal glycemic control and pregnancy outcomes in patients with gestational diabetes mellitus: a prospective cohort study
.
J Clin Endocrinol Metab
2014
;
99
:
4674
4682
13.
McAulay
V
,
Deary
IJ
,
Frier
BM
.
Symptoms of hypoglycaemia in people with diabetes
.
Diabet Med
2001
;
18
:
690
705
14.
Henderson
JN
,
Allen
KV
,
Deary
IJ
,
Frier
BM
.
Hypoglycaemia in insulin-treated type 2 diabetes: frequency, symptoms and impaired awareness
.
Diabet Med
2003
;
20
:
1016
1021
15.
Bolinder
J
,
Antuna
R
,
Geelhoed-Duijvestijn
P
,
Kröger
J
,
Weitgasser
R
.
Novel glucose-sensing technology and hypoglycaemia in type 1 diabetes: a multicentre, non-masked, randomised controlled trials
.
Lancet
2016
; 
388
:
2254
2263
16.
Choudhary
P
,
Ramasamy
S
,
Green
L
, et al
Real-time continuous glucose monitoring significantly reduces severe hypoglycemia in hypoglycemia-unaware patients with type 1 diabetes
.
Diabetes Care
2013
;
36
:
4160
4162
17.
Chamberlain
JJ
,
Dopita
D
,
Gilgen
E
,
Neuman
A
.
Impact of frequent and persistent use of continuous glucose monitoring (CGM) on hypoglycemia fear, frequency of emergency medical treatment, and SMBG frequency after one year
.
J Diabetes Sci Technol
2016
;
10
:
383
388
18.
Reddy
M
,
Jugnee
N
,
El Laboudi
A
,
Spanudakis
E
,
Anantharaja
S
,
Oliver
N
.
A randomized controlled pilot study of continuous glucose monitoring and flash glucose monitoring in people with type 1 diabetes and impaired awareness of hypoglycaemia
.
Diabet Med
2018
;
35
:
483
490
19.
Chamberlain
JJ
,
Gilgen
E
.
Rapid improvement in blood glucose control in a patient with type 1 diabetes and complete blindness using a continuous glucose monitor
.
Clin Diabetes
2014
;
32
:
186
187

Suggested citation:

Hirsch IB, Battelino T, Peters AL, Chamberlain JJ, Aleppo G, Bergenstal RM. Role of Continuous Glucose Monitoring in Diabetes Treatment. Arlington, Va., American Diabetes Association, 2018

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