Diabetics often wear a medical device on their arm called a continuous glucose monitor (CGM). This device helps monitor blood sugar levels throughout the day and night. The CGM contains a small sensor that is inserted under the skin, usually on the back of the upper arm. The sensor measures glucose levels in the fluid between cells (interstitial fluid) and transmits readings wirelessly to a receiver or smartphone app. This allows diabetics to track their blood sugar fluctuations in real time.
How does a continuous glucose monitor work?
A continuous glucose monitor is composed of three main parts:
- A small sensor inserted under the skin that measures glucose levels
- A transmitter that wirelessly sends glucose data to a receiver or smartphone app
- A receiver or app that displays current glucose readings, trends, and alerts
The sensor contains a thin filament coated in glucose oxidase, an enzyme that reacts with glucose. When glucose in the interstitial fluid interacts with this enzyme, a small electric current is generated. The strength of this current provides a measurement of the glucose concentration. The data is transmitted several times per minute to the receiver or app, providing nearly continuous monitoring of glucose fluctuations.
Most CGMs need to be calibrated twice per day by entering a fingerstick blood glucose reading. This helps ensure accuracy of the interstitial fluid measurements. Calibration is not required for some of the newest CGMs, which contain technology to self-calibrate.
What are the benefits of using a CGM?
Wearing a continuous glucose monitor provides several key benefits for diabetes management including:
- Mobile monitoring: Since data is sent wirelessly to a receiver or smartphone, glucose levels can be tracked on the go throughout the day.
- 24/7 readings: The CGM provides glucose measurements around the clock, including overnight while sleeping.
- Trends and patterns: Wearing the CGM for multiple days allows diabetics to observe trends and patterns in their glucose fluctuations.
- Customizable alerts and alarms: Alerts for high or low glucose can be set to notify the diabetic before levels become dangerously out of range.
- Improved control: Research shows CGMs lead to better glucose control and reduced hypoglycemia in both type 1 and type 2 diabetics.
By providing continuous insight into the direction glucose is heading and how fast, CGMs allow diabetics to make timely decisions to keep levels in a healthy range. This leads to tighter overall glucose control and reduced risk of hyperglycemia and hypoglycemia.
What are the main types of continuous glucose monitors?
There are two major categories of CGMs:
Professional systems
- Require physician prescription
- Provide comprehensive reports to share with healthcare provider
- Often covered by insurance with proper documentation of medical necessity
- Require regular sensor replacement by healthcare provider
Examples: Dexcom G6, Medtronic Guardian Connect
Consumer systems
- Can be purchased directly without a prescription
- Primarily for personal use – limited reporting capabilities
- Out-of-pocket cost for users
- User inserts disposable sensors
Examples: Abbott FreeStyle Libre, Senseonics Eversense Now
What are the key components of a CGM system?
The main hardware components of a continuous glucose monitoring system include:
Sensors
- Contain glucose oxidase to measure interstitial glucose
- Inserted via applicator under skin, typically on back of upper arm
- Require replacement every 1-2 weeks depending on device
- Newly developed sensors can last 3-6 months before replacement needed
Transmitter
- Adheres on top of sensor and wirelessly sends glucose data
- Battery powered – lasts 3-6 months before replacement needed
- Transmits via Bluetooth or NFC to receiver or app
Receiver
- Handheld dedicated device that receives and displays glucose data
- Size and form similar to a smartphone but specifically designed for CGM
- Includes adjustable alerts, glucose trend graphs, etc.
Smartphone apps
- Applications developed for use on smartphones/tablets
- Connect with transmitter via Bluetooth to receive and display glucose data
- Provide alerts, trends, reports that can be easily shared
Optimizing each component to work together as an integrated system provides the most effective and convenient CGM experience for diabetes management.
How do you place a CGM sensor on your body?
Proper sensor placement is important for comfort, functionality, and accuracy of CGM readings. The preferred placement for most CGM sensors is on the back of the upper arm.
Steps for sensor application:
- Select an area of skin on the back of the upper arm that is relatively flat – avoid areas with scar tissue or irritation
- Clean the site with an alcohol wipe and allow skin to fully dry
- For sites above elbow, position arm straight out perpendicular to body
- For sites below elbow, position arm parallel to body
- Use the applicator device provided with CGM system to insert thin sensor filament just under skin
- Apply light pressure at site for 30-60 seconds after insertion
- Attach transmitter component of CGM over top of sensor filament
- Use medical adhesive to hold transmitter in place, if needed
Other viable but less optimal sensor sites include the abdomen and back of upper buttocks. Rotation between sensor sites is recommended to avoid skin irritation.
What should you do if your CGM sensor falls off?
It is not uncommon for CGM sensors to sometimes peel off the skin, especially if the adhesion is weakened by moisture or a poorly prepped site. If the sensor falls out, follow these steps:
- Do not attempt to reinsert a used sensor
- Apply a new sensor at a different site following all preparation and insertion instructions
- Enter sensor code into receiver or smartphone app to pair with new sensor
- Perform startup calibration per device instructions
- Temporary use fingerstick glucose checks until new sensor is ready
- Contact your healthcare provider if sensors are falling off repeatedly
Noticing irritation, bleeding, or significant discomfort at the insertion site can also indicate a need for sensor replacement. Be sure to monitor the skin closely around the sensor for signs of trouble.
How long does a CGM sensor last before it needs to be replaced?
The lifespan of CGM sensors varies across different devices but typically ranges from 1-3 weeks before replacement is required:
- Dexcom G6 – up to 10 days
- Abbott FreeStyle Libre – up to 14 days
- Medtronic Guardian Sensor 3 – up to 7 days
- Eversense XL – 90 days
Sensors provide the most accurate data when initially inserted but their performance tends to decline somewhat near the end of the wear period as the sensor site degrades.
The transmitter device that sits over the sensor can often last much longer – from 3 months up to 1 year before battery depletion necessitates replacement.
Following the manufacturer’s guidelines for sensor and transmitter replacement is important to maintain optimal accuracy and consistency of glucose readings.
What is calibration and when is it needed for a CGM?
Calibration involves taking a fingerstick blood glucose reading and entering the value into the CGM’s receiver or app. This is necessary for the CGM to check the accuracy of its interstitial fluid readings against true blood glucose levels.
Calibration is needed in the following circumstances:
- During initial startup – the device requires 2 or more calibrations spaced hours apart to properly initialize
- 12 hours after inserting a new sensor
- Every 24 hours subsequently while wearing the sensor
- Anytime the CGM readings do not match actual blood glucose levels
- After exposure to certain medications or supplements that can interfere with readings
Some newer CGM models use advanced calibration algorithms that reduce the need for daily fingerstick calibrations. However, periodic calibration is still recommended per manufacturer instructions to ensure optimal accuracy.
What accessories are available for continuous glucose monitors?
A variety of accessories are available to enhance the convenience, discretion, and connectivity of CGM systems:
- Adhesive patches – Help keep sensor and transmitter attached securely to skin
- Armbands – Enable discreet wear of the receiver under clothing
- Cases – Protect the receiver and provide color customization
- Charging docks – Streamline recharging the receiver overnight
- Smartwatches – View CGM data directly on watch face, e.g. Apple Watch, WearOS
- Apps – Share data with family/doctors or integrate with health platforms
Accessorizing a CGM system can help optimize comfort, wearability, convenience and enable remote monitoring by friends or family members.
Can you get a CGM through insurance coverage?
Getting a continuous glucose monitor covered by insurance requires:
- A doctor’s prescription indicating medical necessity
- Preauthorization request submitted confirming diabetes diagnosis
- Letter of medical necessity from doctor detailing how CGM improves care
- Use of approved CGM vendors within insurance provider’s network
- Meeting insurance requirements for current use of insulin injections
Those with type 1 diabetes often readily meet the criteria needed for insurance coverage of CGM costs. For type 2 diabetics, demonstrating inadequate glucose control with prescribed medications is key for coverage approval.
Many insurance plans classify CGM devices as durable medical equipment (DME) and have specific requirements for coverage. Working closely with your doctor’s office to provide all needed documentation gives the best chance for getting a prescribed CGM fully covered.
What training is required to start using a CGM?
Proper training helps ensure safe, effective use of continuous glucose monitoring. Recommended CGM training includes:
- Overview of device components – sensor, transmitter, receiver
- Inserting sensor with applicator and starting a new sensor
- Using built-in inserter with integrated sensors, if applicable
- Connecting and pairing transmitter with receiver or smartphone
- Starting calibration process and timing of calibration
- Programming high and low glucose alert levels
- Overview of trend graphs and monitoring capabilities in app
- Charging and maintaining receiver or smartphone app
- Troubleshooting issues like sensor dislodgment, inaccurate readings
- Developing routine of periodic replacement of sensor/transmitter
Your healthcare provider will demonstrate proper device setup and management during initial prescription. Supplemental training can be provided by device manufacturer representatives to reinforce CGM knowledge and skills.
Can I go through airport security with a CGM?
Yes, you can safely go through airport security screening while wearing your continuous glucose monitor. Be sure to follow TSA guidelines:
- Notify security officers you are wearing a CGM before screening
- Present prescription and any medical supplies in separate bag for inspection
- Inform officer if CGM will alarm due to separation from transmitter while screened
- Request visual inspection of CGM instead of full-body scanner
- Do not request to remove sensor – this causes signal disruption
- Know that CGM should not require a pat down unless alarms during screening
Following TSA instructions carefully while communicating about your medical needs makes the screening process straightforward. Be sure to keep supplies and prescription info readily available.
What are the risks and side effects of using a CGM?
Potential risks and side effects of continuous glucose monitors include:
- Skin irritation or allergic reaction to adhesive
- Bleeding or infection at sensor insertion site
- Inaccurate glucose readings from sensor issues
- Frequent or loud alerts disrupting daily life
- Adhesive patch falling off and difficulty keeping sensor attached
- Discomfort or pain from inserting and wearing sensor
- Trouble with insurance coverage for CGM supplies
Proper training on device insertion, hygiene, and use can minimize these risks. Work closely with your healthcare provider to adjust settings, insertion sites, and adhesives if side effects occur.
What advances are being made in CGM technology?
Exciting improvements in continuous glucose monitoring tech focus on several areas:
- Sensor durability – Lasting 6 months to 1 year before replacement needed
- Accuracy – Algorithms utilizing AI for precision glucose readings
- Automated insulin delivery – Integration with pumps to form an artificial pancreas
- Data analytics – Trend analysis to discover patterns and customize care
- Smartphone connectivity – Direct sharing of data and remote monitoring capabilities
Future advancements will lead to more convenient, discreet, and intuitive CGM systems. Improved accuracy and sensor longevity will reduce burdens on users. Tighter device integration and smart data analysis will enable more personalized diabetes therapy.
Conclusion
Continuous glucose monitoring provides invaluable benefits to diabetics by tracking glucose fluctuations in real time. Careful attention to sensor placement, calibration, and replacement are key to getting the most out of CGM technology. Ongoing improvements in accuracy, duration, and connectivity will continue to optimize these devices to improve diabetes outcomes.
