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CGM Data and Report Interpretation

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Device download reports vary by manufacturer and include differing data presentations.

From the Personal Continuous Glucose Monitoring Implementation Playbook from ADCES and AphA. Contributors include: Patricia L. Scalzo, MSN, NP, RN, CDCES, Kelly A. Brock, PharmD, RPh and Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES, FADCES. This effort was supported by Dexcom & Abbott.

The health care professional interprets the personal CGM reports retrospectively and evaluates for glycemic excursions above/below target range, seeking to identify patterns and potential causes for these excursions with the person with diabetes.  

Device download reports vary by manufacturer and include differing data presentations; however, there has been a recent push to focus on use of the Ambulatory Glucose Profile (AGP) report, which was developed by the Park Nicollet International Diabetes Center (IDC) in Minneapolis, Minnesota27. The use of one report would aid in standardization of care and would help to make interpretation more accurate and efficient. The AGP report includes summary statistics, a glucose profile graph and an insulin profile graph or glucose daily calendar graphs. 

Key Metrics 

The 2017 International Consensus on Use of Continuous Glucose Monitoring report published in Diabetes Care provides a detailed description of the 14 key metrics that can be analyzed when reviewing retrospective data. More recently, the International Consensus on Time in Range identified standardized clinical targets for CGM data interpretation, as follows:  

The first priority is to reduce the time spent below range (work to eliminate hypoglycemia) and then focus on decreasing time above range or increasing time in range.  

Number of days CGM is worn 14 days is recommended 

Percentage of time CGM is active  70% of data from 14 days is recommended 

Mean glucose Glucose Management Indicator (GMI)  This used to be called the estimated A1C (eA1C) but now uses an updated formula for converting CGM-derived mean glucose to an estimate of current A1C level. 

Coefficient of Variation (CV)  This is a measure of glycemic variability. A CV of less than or equal to 36% is considered acceptable, >36% is considered unstable and intervention is needed. 

Very High Time Above Range (TAR)  % of readings and time >250 mg/dl  

High Time Above Range (TAR) % of readings and time 181-250 mg/dl 

Time In Range (TIR)  % of readings and time 70-180 mg/dl 

Low Time Below Range (TBR) % of readings and time 54-69 mg/dl  

Very Low Time Below Range (TBR)  % of readings and time <54 mg/dl 

 

Glucose Time In Range Measure  

Glucose time in target range (TIR) is another important measure and Dr. Richard Bergenstal, in 2018, identified correlations of TIR and HbA1C as follows: (Used with permission from Sage Publications. Reference Guide fontegrating Continuous Glucose Monitoring Into Clinical Practice31) 

TIME IN RANGE % (TIR%) AVERAGE HBA1C 
40%8.1% 
50%7.7% 
60%7.3% 
70%6.9% 
80%6.5% 

 

Step 1 Confirm that adequate data are available . For Current CGM users, a minimum of 70% of 2 weeks of data is recommended.34 Fewer days are needed when professional CGM systems are used. 

Step 2 Print out the AGP and ask patients to describe their daily self-management . When are they taking their insulin and how much? When do they wake? When do they eat? Do they exercise and, if so, what type of exercise and when are they doing it? Document this information on the AGP printout. 

Step 3 Ask the patients what they see in the AGP and why they think it may be important . Then listen. Interactive discussion with patients allows them to better understand how their insulin, food and other factors affect their glucose levels and also helps clinicians identify knowledge deficits or behaviors that may not support glycemic goals. 

Step 4 Look for problematic glycemic patterns in the following order of priority: 

  1. Hypoglycemia

  2. Hyperglycemia

  3. Wide glycemic variability.  

Review the overall glucose profile (initial view) to determine the time of day when patterns are occurring, then review the daily graphs to double-check patterns to see if they are clustered on certain days. 

Step 5 Encourage patients to reflect on what they think may be causing the problem and discuss potential solutions.

Step 6 Collaboratively develop an action plan. Make sure patients fully understand the changes they will be making and that they have the knowledge/skills to implement the plan. 

Step 7 Make a copy of the marked up AGP printout for the patient and enter the original into the electronic medical record (EMR). If electronic entry is not possible, copy and paste the AGP into the EMR as a progress note.

 

Additionally, ADCES recommends the use of the DATAA Model for reviewing CGM data, as described by Isaacs et al in the August 2020 issue of “The Diabetes Educator”32:

References: 1 Chehregosha, H, Khamseh, ME, Malek, M, et al. A View Beyond HbA1c: Role of Continuous Glucose Monitoring. Diabetes Therapy. 2019;10, 853–863 2 Sagar R, Abbas A, Ajjan R. Glucose monitoring in diabetes: from clinical studies to real-world practice. Practical Diabetes. 2019;36. 57-62. 10.1002/pdi.2215. 3 Ajjan R, Slattery D, Wright E. Continuous Glucose Monitoring: A Brief Review for Primary Care Practitioners. Advances in Therapy. 2019;36:579-596 4 Aleppo G, Laffel LM, Ahmann AJ, et al. A Practical Approach to Using Trend Arrows on the Dexcom G5 CGM System for the Management of Adults With Diabetes, Journal of the Endocrine Society, Volume 1, Issue 12, 1 December 2017, Pages 1445–1460, https://doi.org/10.1210/js.2017-00388 5 Kudva YC, Ahmann AJ, Bergenstal RM, et al. Approach to Using Trend Arrows in the FreeStyle Libre Flash Glucose Monitoring Systems in Adults, Journal of the Endocrine Society, Volume 2, Issue 12, December 2018, Pages 1320–1337, https://doi. org/10.1210/js.2018-00294 6 Šoupal J, Petruželková L, Grunberger G, et al. Glycemic Outcomes in Adults With T1D Are Impacted More by Continuous Glucose Monitoring Than by Insulin Delivery Method: 3 Years of Follow-Up From the COMISAIR Study. Diabetes Care. 2020 Jan;43(1):37-43. doi: 10.2337/dc19-0888. Epub 2019 Sep 17. 7 Mulinacci G, Alonso T, Snell-Bergeon JK, Shah VN. Glycemic Outcomes with Early Initiation of Continuous Glucose Monitoring System in Recently Diagnosed Patients with Type 1 Diabetes. Diabetes Technology & Therapeutics. 2018;21. 10.1089/ dia.2018.0257. 8 Peters, AL. The Evidence Base for Continuous Glucose Monitoring. Role of Continuous Glucose Monitoring in Diabetes Treatment. American Diabetes Association. 2018 Aug: 3-7. doi: 10.2337/db20181-3 9 American Association of Diabetes Educators Practice Paper. The Diabetes Educator Role in Continuous Glucose Monitoring. 2018. Updated Dec2019; https://www.danatech.org/media/ntgjf2di/diabetescareeducationspecialistrolecgm_aug20.pdf 10 American Diabetes Association. Standards of Medical Care in Diabetes – 2020. Diabetes Care 2020;43(Suppl 1):S77-S88 11 Peters AL, Ahmann AJ, Battelino T, et al.: Diabetes Technology—Continuous Subcutaneous Insulin Infusion Therapy and Continuous Glucose Monitoring in Adults: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2016;101:3922–3937 12 Garber AJ, Handelsman Y, et al. Consensus statement by the American Association of Clinical Endocrinologists and American College of Endocrinology on the comprehensive type 2 diabetes management algorithm - 2020 executive summary. Endocrine Practice 2020, 26 (1): 107-139 13 Danne T, Nimri R, Battelino T, et al. International Consensus on Use of Continuous Glucose Monitoring. Diabetes Care. 2017;40:1631–40 14 Aleppo G, Webb K. Continuous Glucose Monitoring Integration in Clinical Practice: A Stepped Guide to Data Review and Interpretation. Journal of Diabetes Science & Technology. 2018; https://doi.org/10.1177%2F1932296818813581 15 Petrie JR, Peters AL, Bergenstal RM, et al. Improving the clinical value and utility of CGM systems: Issues and Recommendations: A joint statement of the European Association for the Study of Diabetes and the American Diabetes Association Diabetes Technology Working Group. Diabetes Care. Oct 2017, dci170043; DOI: 10.2337/dci17-0043 16 American Diabetes Association. Standards of Medical Care in Diabetes – 2020. Diabetes Care 2020;43(Suppl 1):S77-S88 17 U.S. Centers for Medicare & Medicaid Services. Medicares Coverage of Diabetes Supplies, Services & Prevention Programs. Publication # 11022. Revised 12/01/2019 18 Kompala T, Neinstein A. A New Era: Increasing Continuous Glucose Monitoring Use in Type 2 Diabetes. American Journal Managed Care. 2019 Mar;25(4 Spec No.):SP123-SP126. 19 Welsh JB. Role of Continuous Glucose Monitoring in Insulin-Requiring Patients with Diabetes. Diabetes Technology & Therapeutics. Jun 2018.S2-42-S2-49.http://doi.org/10.1089/dia.2018.0100 20 Heinemann, L, Klonoff, D. C. An Opportunity to Increase the Benefit of CGM Usage: The Need to Train the Patients Adequately. Journal of Diabetes Science and Technology. 2019 https://doi.org/10.1177/1932296819895083 21 Longo, R, Sperling, S. Personal Versus Professional Continuous Glucose Monitoring: When to Use Which on Whom. Diabetes Spectrum. 2019;32. 183-193. 10.2337/ds18-0093 PART SIX: References Personal Continuous Glucose Monitoring Implementation Playbook 61 22 Tanenbaum ML, Adams RN, Lanning MS, et al. Using Cluster Analysis to Understand Clinician Readiness to Promote Continuous Glucose Monitoring Adoption. Journal of Diabetes Science & Technology. 2018;12(6):1108–1115 23 American Diabetes Association. Overcoming Therapeutic Inertia: Accelerating Diabetes Care for Life. American Diabetes Association Summit. Summary of Proceedings. 2019 24 Kazemian P, Shebl FM, McCann N, Walensky RP, Wexler DJ. Evaluation of the Cascade of Diabetes Care in the United States, 2005-2016. JAMA Intern Med. 2019;179(10):1376–1385. doi:10.1001/jamainternmed.2019.2396 25 Rodbard D. Continuous Glucose Monitoring: A Review of Successes, Challenges, and Opportunities. Diabetes Technol Ther. 2016 Feb 1; 18(Suppl 2): S2-3–S2-13. doi: 10.1089/dia.2015.0417 26 Smith MB, Albanese-O’Neill A, Macieira TGR, Yao Y, et al. Human Factors Associated with Continuous Glucose Monitor Use in Patients with Diabetes: A Systematic Review. Diabetes Technology & Therapeutics. Oct 2019.589-601.http://doi.org/10.1089/ dia.2019.0136 27 Johnson ML, Martens TW, Criego AB, Carlson AL, et al. Utilizing the Ambulatory Glucose Profile to Standardize and Implement Continuous Glucose Monitoring in Clinical Practice. Diabetes Technology & Therapeutics. Jun 2019.S2-17-S2-25.http://doi. org/10.1089/dia.2019.0034 28 Danne T, Nimri R, Battelino T, et al. International Consensus on Use of Continuous Glucose Monitoring. Diabetes Care. 2017;40:1631–40 29 Battelino T, Danne T, Bergenstal RM, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations from the International Consensus on Time in Range. Diabetes Care 2019;42:1593-1603. doi10.2337/dci19-0028. 30 Bergenstal, RM. Continuous Glucose Monitoring Data as an Adjunct to A1C. Role of Continuous Glucose Monitoring in Diabetes Treatment. American Diabetes Association. 2018 Aug: 19-20. doi: 10.2337/db20181-3 31 Kruger DF, Edelman SV, Hinnen DA, Parkin CG. Reference Guide for Integrating Continuous Glucose Monitoring into Clinical Practice. 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