EAL

DM: Blood Glucose Self-Monitoring (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To demonstrate the accuracy and effectiveness of the Guardian Continuous Monitoring System (a system that, at the time of this study, did NOT provide real-time sensor glucose values; however sensor glucose readings can be downloaded to a personal computer)
To demonstrate that the application of real-time alarms to continuous monitoring (which the Guardian does provide) alerts users to hypo- and hyperglycemia and reduces excursions in people with diabetes.

Inclusion Criteria:

18 years or older
type 1 diabetes

Exclusion Criteria:

None given.

Description of Study Protocol:

Recruitment

Not provided.

Design

Evaluation of Guardian sensor compared to meter readings; comparison of the number and duration of hypo- and hyperglycemic excursions in the alert group compared with the control group

Blinding used (if applicable): not used

Intervention (if applicable)

Two periods (72 hrs each) of wearing the Guardian: period 1 - alert sensors off for both groups; Period 2, alert sensors on for alert Group and off for control group. User response to alerts was expected to be self monitoring of blood glucose by meter, and then correctly treating the excursion.

Statistical Analysis

Accuracy of Guardian, using the absolute relative error (measure of overall numerical agreement between paired sensor and meter readings)
Ability of Guardian to generate glycemic trends: linear regression and correlation
Accuracy of Guardian hypo- and hyperglycemia alerts: Calculating sensitivity (correct identification of true hypo- or hyperglycemia) and specificity (ability of Guardian to correctly identify the absence of hypo- or hyperglycemia), and producing receiver operator characteristic curves (ROC curves).
Efficacy of Guardian: analysis of low and high glucose excursions (change in number; duration; % of total sensor readings at or below 65 mg/dl and 275 mg/dl or above; and magnitude and duration of daily excursions), with Wilcoxon sign-rank test used to test for significance.

Data Collection Summary:

Timing of Measurements: periodically for two 72 hr periods

Dependent Variables

Blood glucose: measured by
- the Guardian Continuous Monitoring System (Medtronic MiniMed, NOrthridge, CA) and Solutions Software (v3.0)
- Accu-Chek home blood glucose monitor (Roche Diagnostics Corp, Indianapolis IN)
Hyopglycemia: Alert by Guardian at 70 mg/dl
Hyperglycemia: Alert by Guardian at 250 mg/dl

Independent Variables

duration of diabetes

Control Variables

none

Description of Actual Data Sample:

Initial N: 71 (6 men and 29 women in the Alert Group; 17 and 19 in the Control Group). No significant differences were observed between the Alert and Control groups for demographics and baseline characteristics.

Attrition (final N): 66

Age: 44±11.4 years

Ethnicity: 67 Caucasian and 4 other

Other relevant demographics:

duration of diabetes: 23.6±10.6 years
HbA_1c :7.5% (alert); 7.6 (control)
diabetes therapy: 2 (conventional); 15 (multiple daily injections); 54 (continuous subcutaneous insulin injections)
hypoglycemic unawareness: yes=31; no=40.

Anthropometrics:

BMI: 26.7 kg/m²(alert); 26.8 (control).

Location:

Atlanta Diabetes Associates, Atlanta, GA
Virginia Mason Medical Center, Seattle, WA
Sansum Medical Research Institute, Santa Barbara, CA
Diabetes & Glandular Disease, San Antonio, TX
Endocrinology Consultants of East Tennessee, Knoxville, TN

Summary of Results:

Variables

Alert Group

n=32

Control Group

n=36

Statistical Significance of Group Difference

Median decrease in duration of hypoglycemic excursions (minutes), period 2 minus period 1(baseline).

-27.8 (64.4 minutes to 33.6 minutes)

-4.5 (63.8 to 69.6, see note in reviewer comments)

P=0.03

Other Findings

Effectiveness: The mean (median) absolute relative error between home blood glucose meter readings and sensor values was 21.3% (17.3%), and the Guardian, on average, read 12.8 mg/dL below the concurrent home blood glucose meter readings.
The hypoglycemia alert was able to distinguish glucose values less than or equal to 70mg/dL with 67% sensitivity, 90% specificity, and 47% false alerts.
The hyperglycemia alert was able to detect sensor values greater than or equal to 205mg/dL with 63% sensitivity, 97% specificity, and 19% false alerts.
A marginally significant increase in the frequency of hyperglycemic excursions (P=0.07) between period 1 and period 2 was accompanied by a decrease of 9.6 min in the duration of hyperglycemic excursions in the alert group.

Author Conclusion:

Guardian is reasonably accurate while performing continuous glucose monitoring. The subjects' responses to hypoglycemia alerts resulted in a significant reduction in the duration of hypoglycemic excursions; however, overtreating hypoglycemia may have resulted in a marginally significant increase in the frequency of hyperglycemic excursions.

Funding Source:

Reviewer Comments:

Randomization was done using a block design
There was no control over confounding variables (physical activity, food), and no specific or standardized instructions were provided to subjects for treating the hypo- or hyperglycemia
Change in minutes per excursion for hypoglycemia for the control group look as if it should be a +4.5 rather than a -4.5.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	???

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		???
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	???
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		???
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	???
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	???
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	???
7.	Were outcomes clearly defined and the measurements valid and reliable?		???
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	No
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	Yes
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	N/A
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		???
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	???
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes