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.
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.
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.
A condition or circumstance in which a person should not use the device.
Intermittently-Scanned CGM -
This device requires the wearer to swipe the receiver/reader/smartphone over the sensor to obtain glucose data.
Interstitial Glucose Level -
The glucose found in the fluid surrounding the cells in the tissue.
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.
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.
Integrated Continuous Glucose Monitor (icgm) -
An iCGM ss 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.
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.
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.
A glucose sensor is the part of a continuous glucose monitoring (CGM) system that is inserted under the skin and measures interstitial glucose levels.
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).
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.
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.