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Continuous Glucose Monitor (CGM) Glossary

Trying to learn about continuous glucose monitors (CGMs) but starting from scratch? Learning some of the key terms used by healthcare professionals to describe and educate on CGMs will help.
Adjunctive Indication -
A continuous glucose monitor, or CGM, that cannot be used to make treatment decisions. A stand-alone home blood glucose monitor result should be used to make treatment decisions in this case.
AGP (Ambulatory Glucose Profile) -
A standardized, visual report that compiles data from continuous glucose monitoring (CGM), offering a comprehensive overview of a person's glucose trends. The AGP report aids in clinical decision-making by presenting key glucose metrics in an easy-to-interpret format.
Alarm/Alert Thresholds -
Customizable settings in a CGM system that notify the user when glucose levels are too high or too low.
Calibration -
Some CGM systems require fingerstick blood glucose (BG) meter readings in order to generate accurate sensor interstitial glucose readings. The BG meter reading is entered into the device and used for scheduled calibrations or as needed. Calibrations with blood glucose readings are used to ensure that the glucose sensor maintains its accuracy over time. When systems are factory calibrated, fingerstick calibration is not recommended.
CGM Wear Time -
The maximum number of days a sensor can be worn before replacement is required.
Coefficient of Variation -
The Coefficient of Variation (%CV) is calculated by dividing the glucose Standard Deviation by the mean glucose. The %CV is a standardized measure that assesses the magnitude of glucose variability. The larger the %CV, the larger the variability in CGM readings.
Contraindication -
A condition or circumstance in which a person should not use the device.
Factory-Calibrated CGM -
A CGM that does not require manual calibration with a blood glucose meter.
Glucose Management Indicator -
Glucose management indicator (GMI) approximates the laboratory A1C level expected based on average glucose measured using continuous glucose monitoring (CGM) values. The average glucose is most accurate when based on 14 days of CGM data. Differences between GMI and laboratory A1C may reflect differences among an individual’s red blood cell lifespan, how glucose binds to hemoglobin, or due to a recent fluctuation in glucose control. Clinical Reference: Bergenstal, RM, et al. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care. 2018 Nov;41(11):2275-2280.
Interstitial Glucose Level -
The glucose found in the fluid surrounding the cells in the tissue.
Intermittently-Scanned CGM -
This device requires the wearer to swipe the receiver/reader/smartphone over the sensor to obtain glucose data.
Integrated Continuous Glucose Monitor (icgm) -
An iCGM is intended to automatically measure glucose in bodily fluids continuously and to link the CGM to other medical devices used to manage diabetes such as insulin dosing systems, insulin pumps and other digital devices.
Lag Time -
Refers to CGM sensor interstitial glucose readings lagging behind fingerstick blood glucose readings. This occurs because the interstitial fluid glucose that the CGM sensor measures tends to lag behind the fingerstick glucose that the blood glucose meter reads, especially when the glucose level is rapidly changing. The lag time can be up to 15 minutes but is typically less.
MARD (Mean Absolute Relative Difference) -
A measure of CGM accuracy that compares sensor glucose readings to reference blood glucose values under stated research protocols.
No-Code CGM -
A CGM system that does not require the user to enter a sensor code.
Non-adjunctive Indication -
A CGM that can be used to make treatment decisions without the need for a stand-alone home blood glucose monitor to confirm blood glucose results.
Personal CGM -
A CGM device owned and used by a person with diabetes, continuously or intermittently. Persons with diabetes and supporting individuals (i.e., parents) use the information in real time to make diabetes management decisions.
Predictive Alerts -
Alerts generated by CGM systems that predict upcoming hypoglycemia or hyperglycemia based on glucose trends.
Professional CGM -
Clinic-based and clinic-owned CGM devices that are placed on the patient in the provider’s office and used on a short-term basis and returned following specified monitoring period. Data may be blinded or visible to the device wearer.
Real-time CGM -
A device that automatically transmits glucose data to a receiver or compatible smartphone.
Receiver or Reader -
The receiver (reader) or compatible smart device receives glucose data from the transmitter and displays current levels, historical trends in levels, and arrows to show direction that glucose is heading.
Sensor -
A glucose sensor is the part of a continuous glucose monitoring (CGM) system that is inserted under the skin and measures interstitial glucose levels.
Sensor Expiration -
The date or time when a CGM sensor is no longer usable and must be replaced.
Sensor Insertion Site -
The recommended body locations where a CGM sensor can be placed for optimal performance.
Sensor Overlap -
When a new sensor is applied before the old one is removed, allowing for a transition and continuous data collection.
Skin Adhesive/Overpatch -
Products used to secure a CGM sensor to the skin for extended wear time.
Smart Transmitter -
A reusable device worn externally over an inserted sensor that powers the sensor and sends glucose information to the mobile device for display in an app (currently Eversense ® specific).
Standalone Device -
A CGM that transfers information directly to a receiver and does not need another connected device to provide the glucose data.
Standard Deviation -
The extent of glucose readings that are above and below the mean. A measure of variation.
Time in Range (TIR) -
The percentage of time that glucose levels are within a specified glucose range (target, above or below).
Transmitter -
A small, reusable or disposable transmitter connected to the sensor allows the system to send real-time glucose readings wirelessly to another device that displays the glucose data.
Trend Arrows -
Trend arrows indicate the direction the glucose is heading and allows anticipatory changes to be made to prevent hyper/hypoglycemia.
Urgent Low Glucose Alarm -
A built-in alert that warns the user of critically low glucose levels requiring immediate action.
User-Defined Glucose Range -
The customizable glucose target range set by the user or health care provider for optimal diabetes management, useful in certain populations including pregnant or elderly patients among others. The User-Defined Glucose Range will not appear on the AGP report.
Virtual Diabetes Clinic -
A remote monitoring system where CGM data is shared with health care providers for telehealth-based diabetes management.
Warm-up Time -
The amount of time it takes for the sensor to calibrate after it is placed under the skin, before the data can be transmitted to the receiver. The warm-up time varies for different devices. During the warm-up time, the person with diabetes must check a fingerstick blood glucose for treatment decisions.
Wearable Technology Integration -
The capability of CGM devices to sync with smartwatches, fitness trackers or other wearable tech.

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