Lexicon
CGM
Also known as Continuous Glucose Monitor, Continuous Glucose Monitoring
Definition
Continuous glucose monitoring, used either in real-time or intermittently scanned mode, addresses many limitations inherent in HbA1c testing and self-monitoring of blood glucose. [1] Glycemic control can be monitored by people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring devices, alongside laboratory HbA1c. [2] CGM devices are now considered the standard of care for people with type 1 diabetes, while uptake in type 2 diabetes has been slower and initially focused on those receiving intensive insulin therapy. [3]
How it works
CGM devices collect data at 1-5 minute intervals, obtaining information on glycemic excursions and periods of asymptomatic hypoglycemia or hyperglycemia that HbA1c does not provide. [4] HbA1c does not reflect intra- and inter-day glycemic excursions that may lead to acute events such as hypoglycemia or postprandial hyperglycemia, both of which have been linked to microvascular and macrovascular complications. [1] Glycemic variability indices beyond the standard deviation and coefficient of variation, in particular the mean amplitude of glycemic excursion, are emerging as identifiers of early dysglycemia. [5] Continuous glucose monitoring is used to guide nutrition choices, with randomized-trial evidence supporting its role in shaping dietary lifestyle interventions that improve glycemia and body weight in type 2 diabetes [6].
Connected concepts
How it's measured
Meaningful interpretation of CGM requires adequate data, and studies show that using CGM for greater than 70% of the most recent 14 days correlates strongly with 3 months of mean glucose and hyperglycemia metrics. [7] Standardized, internationally agreed CGM-derived metrics such as time in range, time below range, time above range, and glycemic variability are recommended for use in clinical practice and clinical trials. [4] Accuracy differs across devices, and FDA-cleared integrated CGM systems with published performance data can be used non-adjunctively to directly inform insulin dosing, whereas some non-integrated devices require confirmatory blood glucose testing. [8]
What levels mean
For type 1 and type 2 diabetes the consensus goal is greater than 70% of time in the 70-180 mg/dL (3.9-10.0 mmol/L) target range, with less than 4% of time below 70 mg/dL (3.9 mmol/L) and less than 1% below 54 mg/dL (3.0 mmol/L). [7] Time in range and A1C both correlate with average glucose
Community knowledge
## Continuous Versus Point-In-Time Testing
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- 1.Danne T, Nimri R, Battelino T, Bergenstal RM, Close KL, DeVries JH, Garg S, Heinemann L. International Consensus on Use of Continuous Glucose Monitoring. Diabetes Care · 2017
- 2.Sacks DB, Arnold M, Bakris GL, Bruns DE, Horvath AR, Lernmark Å, Metzger BE, Nathan DM. Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus. Diabetes Care · 2023
- 3.Ajjan RA, Battelino T, Cos X, Del Prato S, Philips JC, Meyer L, Seufert J, Seidu S. Continuous glucose monitoring for the routine care of type 2 diabetes mellitus. Nat Rev Endocrinol · 2024
- 4.Battelino T, Alexander CM, Amiel SA, Arreaza-Rubin G, Beck RW, Bergenstal RM, Buckingham BA, Carroll J. Continuous glucose monitoring and metrics for clinical trials: an international consensus statement. Lancet Diabetes Endocrinol · 2023
- 5.Zahalka SJ, Galindo RJ, Shah VN, Low Wang CC. Continuous Glucose Monitoring for Prediabetes: What Are the Best Metrics? J Diabetes Sci Technol · 2024
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