Continuous Glucose Monitors (CGMs)

Here is some information about CGMs, a key technology for the management of type 1 diabetes (T1D).

 CGMS for Endocrinologists and Health Care ProvidersCGMs for Engineers and Mathematicians
What is type 1 diabetes? Here is more information about type 1 diabetes.Type 1 diabetes (T1D) is a chronic autoimmune condition without a cure where the pancreas stops producing insulin.Type 1 diabetes (T1D) is a lifelong condition where one's pancreas does not produce insulin like it is supposed to.
What did patients used to do before CGMs?Many people, even today, check their blood sugar by using a needle to draw a small amount of blood from their finger several times a day. However, this hurts, provides relatively little information, and creates calluses.Patients checked their blood sugar by using a needle to draw a small amount of blood from their finger several times a day. However, this hurts, provides relatively little information, and creates calluses. Today, many people still use meters instead of CGMs because of the cost and other barriers.
How do CGMs work? Learn more here.CGMs read blood glucose numbers (BGs) from the patient's interstitial fluid every few minutes.CGMs wirelessly send a continuous stream of blood glucose (BG) data to patients with diabetes.
Why are CGMs helpful? Learn more by looking at SURF's publications on CGMs here.CGM data informs patients so they can prevent hypo- and hyperglycemia. CGMs also lessen fingersticks.CGMs empower patients to act on their BG data to have better BG control.
Commercial CGMs. Learn more about comparing these CGMs here.Dexcom G6, Dexcom G5, Abbott FreeStyle Libre, Medtronic Guardian Sensor 3, and Senseonics Eversense. Dexcom G6, Dexcom G5, Abbott FreeStyle Libre, Medtronic Guardian Sensor 3, and Senseonics Eversense.
Dexcom G60 fingerstick calibrations required
The CGM alarms when there is an out-of-range blood sugar
Covered by Medicare
Expensive
The sensor has a 10-day wear length
Accurate
CGM data is viewable on multiple devices
The Dexcom Clarity analytics tool has many features and is user-friendly for health care providers (HCPs) and patients
Dexcom G52 fingerstick calibrations required daily
The CGM alarms when there is an out-of-range blood sugar
Covered by Medicare
Expensive
The sensor has a 7-day wear length
Accurate
The sensor is large and easily noticed
CGM data is viewable on multiple devices
The Dexcom Clarity analytics tool has many features and is user-friendly for HCPs and patients
Abbott FreeStyle Libre0 fingerstick calibrations required
The patient must scan a reader device over their CGM to see their BG
Covered by Medicare
Inexpensive
The sensor has a 14-day wear length
The sensor is small and discreet
Ages 18+
CGM data is not viewable on many devices
The Libre View analytics tool has some features and is user-friendly for HCPs but not patients
Medtronic Guardian Sensor 32 fingerstick calibrations required daily
The CGM alarms when there is an out-of-range blood sugar
Not covered by Medicare
Expensive
The sensor has a 7-day wear length
Inaccurate
The sensor is large and easily noticed
CGM data is not viewable on many devices
The Libre View analytics tool has some features and is user-friendly for HCPs but not patients
Senseonics EversenseThe sensor is implanted underneath the patient skin in a short surgery, but there is also a transmitter on top of the patient's skin
2 fingerstick calibrations required daily
The CGM vibrates when there is an out-of-range blood sugar
Not covered by Medicare
Expensive
The sensor has a 90-day wear length (soon to be 180)
Accurate
Ages 18+
CGM data is not viewable on many devices
There is no analytics tool
CGMs on the horizon. Learn more here. Libre 2.0: optional alerts, interoperability
Dexcom G7: extended wear, decision support
Eversense: longer wear
WaveForm Cascade: longer wear
Biolinq: small, press-on insertion
Non-invasive CGMs: using tears, breath, tattoos, or pacifiers
Libre 2.0: interoperability
Dexcom G7: decision support
Eversense: longer wear
WaveForm Cascade: longer wear
Biolinq: press-on insertion
Non-invasive CGMs: using tears, breath, tattoos, or pacifiers
CGM metrics. Learn more about CGM metrics and SURF's work with them here.Time In Range (TIR), Glucose Management Indicator (GMI), Average/Mean Glucose, Standard Deviation (SD), and Coefficient of Variation (CV)Time In Range (TIR), Glucose Management Indicator (GMI), Average/Mean Glucose, Standard Deviation (SD), and Coefficient of Variation (CV)
Time In/Above/Below Range (TIR, TAR, TBR)The percent of time that a person’s BG is in/above/below their target range. The percent of time that a person’s BG is in/above/below their target range.
Glucose Management Indicator (GMI)Estimated HbA1C. SURF student Josh Grossman is working on improving HbA1c estimates with CGM data.Estimated HbA1C. SURF student Josh Grossman is working on improving HbA1c estimates with CGM data.
Other metrics. Learn more here.Average/mean glucose: average of all BG values over a period of time.
SD: the range/spread of BG values.
CV: (SD / mean glucose) x 100%
Average/mean glucose: average of all BG values over a period of time.
SD: the range/spread of BG values.
CV: (SD / mean glucose) x 100%
How can you act on CGM data? Learn more about how SURF is acting on CGM data here and see SURF's publications on CGMs here.1) Remind families to upload their CGM data.
2) Adjust the patient's insulin pump settings.
3) Share average CGM metrics from the patient population.
4) Determine if Dexcom G6 users can get 10 days out of the sensor (because of the weak adhesive).
5) Share average basal rates, insulin sensitivity, etc. across ages and weights to help newly diagnosed families.
1) Evaluate new devices.
2) Determine whether hypo- or hyperglycemia occurs more to change insulin pump settings to be more/less aggressive.
3) Find out issues and safety concerns with devices.
4) Determine if, after a patient's BG has been high or low for a long period of time, it takes more aggressive treatment to get back in range.
5) Identify unusual patient behavior (like large boluses, etc.).
6) Standardize CGMs to learn about BG patterns.
7) Use CGM data to help physicians offer personalized feedback for each of their patients. SURF student Josh is working on this.
8) Develop a heat map for physicians to help them determine how often to reach out to patients about their BG control.
What is a closed-loop system?Closed-loop systems are a collaboration between the insulin pump and the CGM. They work together to modulate basal rates to help patients have better BG control.Closed-loop systems use process control algorithms to change insulin dosing based on CGM readings.
Commercial closed-loop systemsTandem/Dexcom Control-IQ: increases TIR, improves quality of life, 0 fingerstick calibrations required
Medtronic 670G: increases TIR, excessive alarms, 2 daily fingerstick calibrations required
Tandem/Dexcom Control-IQ: increases TIR, improves user-friendliness, 0 fingerstick calibrations required
Medtronic 670G: increases TIR, excessive alarms, 2 daily fingerstick calibrations required
Non-commercial closed-loop system: LoopLoop is a DIY app where a RileyLink connects a Medtronic/OmniPod pump with the Dexcom G6, improving the patient's quality of life. However, Loop is inaccessible to most patients.Loop is a DIY app made by T1D parents where old Medtronic/OmniPod pumps are connected to the Dexcom G6 with a RileyLink. Loop improves TIR but is difficult to set up and troubleshoot.
Future closed-loop systems. Learn more here.Medtronic 780G: automatic correction boluses
Tidepool Loop: interoperability
Bigfoot Biomedical/Abbott: data visible on a phone
OmniPod/Dexcom Horizon: controlled from a phone
Beta Bionics iLet/Dexcom: dual-hormone system (insulin and glucagon)
Lilly/Dexcom: data visible on a phone
Automated meal boluses
Medtronic 780G: automatic correction boluses
Tidepool Loop: interoperability
Bigfoot Biomedical/Abbott: data visible on a phone
OmniPod/Dexcom Horizon: controlled from a phone
Beta Bionics iLet/Dexcom: dual-hormone system (insulin and glucagon)
Lilly/Dexcom: data visible on a phone
Automated meal boluses by comparing actual BGs to predicted BGs with and without meals

Jamie’s Story

Jamie was diagnosed with type 1 diabetes when she was only 1 year old. Before she knew she had this chronic condition without a cure, she threw up every day, she didn’t want to play, she didn’t want to eat, she was always really thirsty, and she would just lay down, totally lacking energy. Because she was so young that she couldn’t communicate her feelings in words, her parents were terrified that she might die. 

Since Jamie was diagnosed 14 years ago, she has always been fascinated with how technology is helping her life become better and easier. She became one of the youngest insulin pump and continuous glucose monitor (CGM) users soon after her diagnosis, participated in a clinical trial for the first commercial “artificial pancreas” system, and is now Looping (a non-FDA approved artificial pancreas system). One of her favorite technologies is the CGM because it alerts her when her blood sugar numbers are out of range, allowing her to act on this data and minimize the effects of out-of-range blood sugars like from before her diagnosis.

This interest in technology and medicine is what led her to become the Director of Scientific Communications for SURF. Jamie has loved working with SURF because they are doing groundbreaking work to help spread medical technology to all. Jamie believes that SURF’s work with CGMs is helping to find a cure and are greatly improving peoples’ lives, including hers. Jamie is so grateful for SURF for helping to make these lifelong dreams come true.