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Introduction Continuous blood glucose monitor- ing (CBGM) systems are often used in diabetes care when there is uncer- tainty regarding glycaemic trends (usually demonstrating a discor- dance between home blood glucose monitoring [HBGM] results and clinic HbA1c measurements) or in patients with, or suspected of, hypo- glycaemic unawareness. There is some controversy about the use of CBGM versus HBGM with regard to its overall efficacy in improving glycaemic control in the form of the HbA1c. 1–3 With the use of CBGM being rel- atively expensive and its efficacy in diabetes care remaining uncertain, 4 we decided to study the use of CBGM in a secondary care setting with regard to glycaemic pattern identification and its subsequent impact on overall diabetic control and patient symptoms. Methods We audited the records of 42 consec- utive patients who attended a district hospital over a two-year period who underwent 72-hour CBGM from 2005–2006. Data were obtained ret- rospectively from clinical and com- puterised notes. Patient selection for CBGM was undertaken by a consult- ant diabetologist, or a diabetes spe- cialist nurse, or a specialist registrar. CBGM was performed either because of inconsistent HBGM measurements as compared to HbA1c results, or because of con- cerns about impaired hypogly- caemic awareness. Hypoglycaemic unawareness was suspected in patients who had experienced unex- plained hypoglycaemia requiring correction by a third party, or in patients whose HBGM records revealed low glucose levels in the absence of symptoms. We analysed the changes in the overall glycaemic control by com- paring HbA1c before and after CBGM. We also examined glycaemic trends during the 72-hour period. In particular, we identified noctur- nal hypoglycaemia and hypogly- caemic unawareness during the day, based on the following criteria. Nocturnal hypoglycaemia was defined by a glucose reading on the continuous glucose monitoring sys- tem (CGMS) of <3.5mmol/L with- out interruption of the patient’s sleep patterns; hypoglycaemic unawareness during the day was defined as a fall of glucose measure- ment to <3.5 mmol/L for a period of greater than half an hour in the absence of symptoms. All patients who had a 72-hour CBGM done were then followed up by a diabetes specialist nurse. Consecutive HbA1c readings were obtained before and after CBGM and the reasons for prompting the test were identified. Adjustments to insulin treatment or alteration of dosage and insulin regimen were made at consultation once the CBGM results were available. Following this, patients were then followed up by telephone approxi- mately two weeks later, with further follow up by telephone or clinic review determined by need. All patients were given appointments for review with HbA1c readings within four to six months following CBGM. ORIGINAL S HORT REPORT Pract Diab Int July/August 2008 Vol. 25 No. 6 Copyright © 2008 John Wiley & Sons 239 Continuous blood glucose monitoring: does it really affect diabetic control? JM Ng*, J Patel, H Gibson, PE Jennings ABSTRACT There remains uncertainty concerning the use of continuous blood glucose monitoring (CBGM) systems in the assessment and management of diabetes control. We examined 42 consecutive patients who attended a district hospital over a two- year period and had CBGM performed to determine if the data obtained had benefited patient care. There was an easily identifiable pattern in the 72-hour glycaemic trend in 25 patients. Out of this number, 15 patients had nocturnal hypoglycaemia. The average follow-up time was seven months, whilst the total daily dose of insulin administered per day fell insignificantly from 55.7 initially to 55.4 units/24hr. HbA1c improved marginally over this time in all patients, reducing from 8.88% to 8.55%. CBGM offers a marginal advantage over home blood glucose monitoring where glycaemic patterns are poorly understood. However, from our observations, the use of CBGM independently in the management of glycaemic control in diabetes is, overall, ineffective, but it may be useful in the identification of nocturnal hypoglycaemia. Copyright © 2008 John Wiley & Sons. Practical Diabetes Int 2008; 25(6): 239–240 KEY WORDS continuous blood glucose monitoring (CBGM); hypoglycaemia JM Ng, MB BCh (Belf), MRCP, Specialist Registrar, Diabetes and Endocrinology J Patel, MBBS, Senior House Officer, Accident & Emergency H Gibson, Diabetes Clinical Nurse Manager PE Jennings, BMedSci, BM, BS, DM, FRCP, Consultant Physician and Honorary Senior Lecturer in Diabetes and Endocrinology Diabetes Centre, York Hospital, York, UK *Correspondence to: Dr JM Ng, MB BCh, MRCP, Diabetes Centre, York Hospital, Wigginton Road, York YO31 8HE, UK; e-mail: [email protected] Received: 12 November 2007 Accepted in revised form: 12 March 2008

Continuous blood glucose monitoring: does it really affect diabetic control?

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IntroductionContinuous blood glucose monitor-ing (CBGM) systems are often usedin diabetes care when there is uncer-tainty regarding glycaemic trends(usually demonstrating a discor-dance between home blood glucosemonitoring [HBGM] results andclinic HbA1c measurements) or inpatients with, or suspected of, hypo-glycaemic unawareness. There issome controversy about the use ofCBGM versus HBGM with regard toits overall efficacy in improving glycaemic control in the form of the HbA1c.1–3

With the use of CBGM being rel-atively expensive and its efficacy indiabetes care remaining uncertain,4we decided to study the use ofCBGM in a secondary care settingwith regard to glycaemic patternidentification and its subsequentimpact on overall diabetic controland patient symptoms.

MethodsWe audited the records of 42 consec-utive patients who attended a districthospital over a two-year period whounderwent 72-hour CBGM from2005–2006. Data were obtained ret-rospectively from clinical and com-puterised notes. Patient selection forCBGM was undertaken by a consult-ant diabetologist, or a diabetes spe-cialist nurse, or a specialist registrar.

CBGM was performed eitherbecause of inconsistent HBGMmeasurements as compared toHbA1c results, or because of con-cerns about impaired hypogly-caemic awareness. Hypoglycaemicunawareness was suspected in

patients who had experienced unex-plained hypoglycaemia requiringcorrection by a third party, or inpatients whose HBGM recordsrevealed low glucose levels in theabsence of symptoms.

We analysed the changes in theoverall glycaemic control by com-paring HbA1c before and afterCBGM. We also examined glycaemictrends during the 72-hour period.In particular, we identified noctur-nal hypoglycaemia and hypogly-caemic unawareness during the day,based on the following criteria.Nocturnal hypoglycaemia wasdefined by a glucose reading on thecontinuous glucose monitoring sys-tem (CGMS) of <3.5mmol/L with-out interruption of the patient’ssleep patterns; hypoglycaemicunawareness during the day wasdefined as a fall of glucose measure-

ment to <3.5 mmol/L for a periodof greater than half an hour in theabsence of symptoms.

All patients who had a 72-hourCBGM done were then followed up by a diabetes specialist nurse.Consecutive HbA1c readings wereobtained before and after CBGMand the reasons for prompting thetest were identified. Adjustments toinsulin treatment or alteration ofdosage and insulin regimen weremade at consultation once theCBGM results were available.Following this, patients were thenfollowed up by telephone approxi-mately two weeks later, with furtherfollow up by telephone or clinicreview determined by need. Allpatients were given appointmentsfor review with HbA1c readingswithin four to six months followingCBGM.

ORIGINAL SHORT REPORT

Pract Diab Int July/August 2008 Vol. 25 No. 6 Copyright © 2008 John Wiley & Sons 239

Continuous blood glucose monitoring: does it really affect diabetic control?JM Ng*, J Patel, H Gibson, PE Jennings

ABSTRACTThere remains uncertainty concerning the use of continuous blood glucose monitoring(CBGM) systems in the assessment and management of diabetes control.

We examined 42 consecutive patients who attended a district hospital over a two-year period and had CBGM performed to determine if the data obtained had benefitedpatient care.

There was an easily identifiable pattern in the 72-hour glycaemic trend in 25 patients.Out of this number, 15 patients had nocturnal hypoglycaemia. The average follow-up timewas seven months, whilst the total daily dose of insulin administered per day fellinsignificantly from 55.7 initially to 55.4 units/24hr. HbA1c improved marginally over thistime in all patients, reducing from 8.88% to 8.55%.

CBGM offers a marginal advantage over home blood glucose monitoring whereglycaemic patterns are poorly understood. However, from our observations, the use ofCBGM independently in the management of glycaemic control in diabetes is, overall,ineffective, but it may be useful in the identification of nocturnal hypoglycaemia.Copyright © 2008 John Wiley & Sons.

Practical Diabetes Int 2008; 25(6): 239–240

KEY WORDScontinuous blood glucose monitoring (CBGM); hypoglycaemia

JM Ng, MB BCh (Belf), MRCP, SpecialistRegistrar, Diabetes and Endocrinology J Patel, MBBS, Senior House Officer,Accident & EmergencyH Gibson, Diabetes Clinical Nurse ManagerPE Jennings, BMedSci, BM, BS, DM,

FRCP, Consultant Physician and HonorarySenior Lecturer in Diabetes andEndocrinology Diabetes Centre, York Hospital, York, UK

*Correspondence to: Dr JM Ng, MB BCh,

MRCP, Diabetes Centre, York Hospital,Wigginton Road, York YO31 8HE, UK; e-mail: [email protected]

Received: 12 November 2007Accepted in revised form: 12 March 2008

SR Ng 123.07.qxp 21/7/08 10:13 Page 1

ORIGINAL SHORT REPORT

Continuous blood glucose monitoring: does it really affect diabetic control?

ResultsThe mean age of the patients was 54years with a mean duration of dia-betes of 7.5 years. Thirty-six patientswere on multiple dose regimeninsulin (MDI) and six were onbiphasic therapy. Two patientschanged on to MDI followingCBGM. Of the 42 patients analysed,38 patients were on analogueinsulins. There were 23 females and19 males.

The average follow up time forthe whole group of patients wasseven months, whilst the total daily dose of insulin admin-istered per day fell insignificantly from 55.7 units/24hr initially to55.4 units/24hr. There were alter-ations to the time of insulin admin-istration to counteract hypogly-caemia. The average night-timeinsulin dose fell from 22.7 to19.8 units. The average HbA1c

improved marginally in all patientsfrom 8.88% to 8.55%.

Of the 42 patients, there was anidentifiable glycaemic pattern in 25patients: 15 patients had nocturnalhypoglycaemia, three had persistenthyperglycaemia, three had post-prandial hyperglycaemia, two haddaytime hypoglycaemia, and twohad nocturnal hyperglycaemia.Despite alterations to insulin dosesand regimen, HbA1c in this particu-lar group of patients with identifi-able trends only improved from8.48% to 8.31%.

Patients with impaired hypo-glycaemic awareness were morelikely to have nocturnal hypogly-caemia and, following adjustmentsin their regimens, reported signifi-cant improvements.

A total of 14 patients had HBGMreadings which were discordantwith the recording on the CGMS.The records revealed higher glu-cose levels than had previouslybeen recorded by HBGM. Thisgroup continued with the same pattern of poor self-managementdespite similar nurse contacts andadjustments to insulin regimens.There were no improvements totheir HbA1c readings.

DiscussionIn more than half of the cases,identifiable glycaemic trends were

noted after a 72-hour monitoringperiod, but the overall diabeticcontrol in the form of an HbA1c

did not significantly improvedespite an alteration of thepatient’s individual insulin regi-men after six months.

Most symptomatic patients bene-fited from the intervention, especially with regard to the avoid-ance of nocturnal hypoglycaemia.However, no improvement in theaverage HbA1c was seen, althoughsome patients did have significantimprovements in HbA1c. A previousstudy compared regular HBGM andCBGM, and found similar resultswith regard to overall glycaemiccontrol but significant improve-ments relating to avoidance of hypo-glycaemia.5

The patients without identifi-able glycaemic trends were gener-ally those with poor HbA1c andinconsistent results in their previ-ous HBGM records. Individualintervention by the diabetes special-ist nurse was ineffective.

It is possible that the improve-ment of glycaemic control requiresseveral factors in addition to theidentification of glycaemic trend.Patient education and understand-ing of their diabetes, with regularself-monitoring and titration ofinsulin, are likely important factors;patients would therefore be morelikely to benefit from intervention ifthey are engaged in their diabetesmanagement.

We conclude that the use ofCBGM is effective in the identifica-tion of causes of hypoglycaemicunawareness, in particular noctur-nal hypoglycaemia. Correcting thisproblem improves patients’ symp-toms but does not affect their overall glycaemic control. It is alsouseful where glycaemic patterns

are poorly understood with HBGM.However, even when a glycaemictrend is identified, patients’ controldoes not always improve withinsulin titration.

Therefore this device is bestreserved for use in patients’ carewhere there is a clearly definedobjective, such as improving hypo-glycaemic awareness, or wherepatients wish to achieve better glu-cose control themselves. Due to theexpensive nature of this device,more studies are needed to furtheranalyse its effectiveness in clinicalcare before it is used as a routineinvestigation in diabetic patientswith poor glycaemic control.

Conflict of interest statementThere are no conflicts of interest.

References1. Klonoff DC. Continuous glucose

monitoring: roadmap for 21st cen-tury diabetes therapy. Diabetes Care2005; 28(5): 1231–1239.

2. Deiss D, Bolinder J, Riveline JP, et al.Improved glycemic control in poorlycontrolled patients with type 1 dia-betes using real-time continuous glu-cose monitoring. Diabetes Care 2006;29(12): 2730–2732.

3. Garg SK, Schwartz S, Edelman SV.Improved glucose excursions usingan implantable real-time continuousglucose sensor in adults with type 1diabetes. Diabetes Care 2004; 27(3):734–738.

4. Vidya K, Sudhir R, Mohan V.Continuous Glucose MonitoringSystem – Useful but Expensive Toolin Management of Diabetes. J AssocPhysicians India 2004; 52: 587–590.

5. Tanenberg R, Bode B, Lane W, et al.Use of the Continuous GlucoseMonitoring System to guide therapyin patients with insulin-treated dia-betes: a randomized controlled trial.Mayo Clin Proc 2004; 79(12):1521–1526.

240 Pract Diab Int July/August 2008 Vol. 25 No. 6 Copyright © 2008 John Wiley & Sons

Key points

• The use of continuous blood glucose monitoring (CBGM) and its use inimproving glycaemic control remain uncertain

• CBGM is useful in picking up hypoglycaemic unawareness, nocturnalhypoglycaemia and where there is discordance between home bloodglucose readings and HbA1c

• CBGM does not seem to improve overall glycaemic control in patients,despite changes to their insulin regimen and close clinical follow up

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