Getting started with a Continuous Glucose Monitor (CGM) is like getting started with a new smartphone. There is some initial setup to be done, and you’ll have to explore and practice a bit to get used to the controls, but before long, you’ll be zipping through your everyday CGM functions like a pro.
What is CGM?
Continuous Glucose Monitoring (CGM) is a method of monitoring glucose levels for people with insulin-dependent diabetes. In studies, CGM has improved outcomes for users by increasing time in range (TIR) and reducing the risk of diabetes complications. CGM systems can be used alone or with insulin pumps to create an artificial pancreas. Newer CGM systems have released some excellent new features, including:
No more fingerstick calibration
Overpatch for additional adhesion
Urgent “low soon” alerts
Acetaminophen blocking (to eliminate acetaminophen-induced inaccurate readings)
There are a few components in a Continuous Glucose Monitoring system.
First is the CGM sensor, a small wire implanted just under the skin’s surface, where it can measure glucose levels in the fluid surrounding your skin and fat cells. These readings are different than blood glucose readings but can be used similarly. Some newer devices don’t even require calibration – the regular use of a blood sugar meter to maintain system accuracy – though you should always check your blood glucose levels with a meter before treating hypoglycemia or hyperglycemia.
The applicator is a device used to implant the sensor. In most Continuous Glucose Monitoring systems, you put the sensor in the applicator and press the applicator against your skin.
After that, you’ll have to connect a transmitter. That’s the piece that takes the data and broadcasts it day and night via Bluetooth to the device you’ll use to read and track your glucose levels. CGM systems today have low-profile sensors and transmitters, so you don’t have a bulky and cumbersome electronic device hanging off your skin.
Most CGM systems come with a receiver, the device you’ll use to read the data. You can also track your readings on an app downloaded to your smartphone or another smart device.
With these four or five CGM components, you’ll be able to watch your glucose levels all day and night without sticking your fingertips over and over. That CGM data will help you and your doctor make more effective treatment decisions and lifestyle adjustments, increase your time in range and reduce the risk of dangerous highs and lows.
Who can use a CGM?
Currently, CGMs are typically recommended for people with type 1 diabetes, but research is being conducted to determine if CGM systems can help people with type 2 diabetes.
CGMs require a doctor’s prescription. Your doctor might recommend a CGM system if you are on intensive insulin therapy (AKA tight blood sugar control), have hypoglycemia unawareness, or need to increase your time in range (TIR). CGM can be used temporarily to improve your treatment plan or long-term to help you stay in range and reduce your risk of complications.
Using a CGM system to monitor your blood sugar
Be sure to read your CGM user manual before using a CGM system.
User manual for Freestyle Libre 2
You’ll start by choosing whether to use the receiver or your smart device to receive CGM data. Medicare requires the use of the receiver, but you can use both for convenience – and because the CGM mobile apps offer more features than the receivers alone.
Do not open any CGM packaging until you’re ready for application.
Do not use any CGM components that appear damaged or have damaged or open packaging.
Do not use CGM components that are past their “use by” date.
You will need alcohol wipes and (possibly) your blood sugar meter.
Your smartwatch can display Dexcom G6 data.
Make sure at least one CGM display device is turned on at all times.
Turn off automatic OS updates on your display device. Update manually and check CGM settings every time.
List of display devices that are compatible with Dexcom G6
Compatibility guide for Freestyle Libre 2
Setting up the app
Once you download the app, on-screen instructions will guide you through the initial setup. If you’ve used the app in the past, your settings and CGM data will typically be imported. You’ll set your target range and enable the necessary permissions like overriding Do Not Disturb. Bluetooth needs to be on, and you’ll need the codes from your components. Without the codes, you’ll have to use your blood glucose meter to calibrate your devices daily.
Setting up the receiver
Be sure to follow the exact instructions that come with your CGM system. Some models require that you insert your sensor and start a session before setting up the receiver.
Turn on your receiver and wait for loading to finish, if necessary. Follow the on-screen instructions to set the date, time, and glucose thresholds, and enter your component codes. Again, without those codes, you’ll have to calibrate your CGM device frequently.
Some models don’t offer codes and will require frequent calibration.
Inserting your sensor
Wash your hands before getting started!
Freestyle Libre 2 insertion tutorial
Choose an appropriate site according to the instructions that come with your CGM system. Some models require placement on the back of the arms, while others can be placed on the abdomen or lower back.
Place at least three inches from your insulin injection site.
Don’t use a site you recently used.
Don’t use on a bony area.
Don’t use in an area that is often rubbed by clothing or slept on.
Do not touch the adhesive with anything until you place it against your skin in the desired location.
For the best possible adhesion, shave and clean the site. Wipe the area with an alcohol prep pad and let it air dry. If the sensor is not already connected to the applicator, connect the two pieces according to the instructions that came with your system.
When ready, place the applicator as instructed over the chosen insertion site. You might have to remove a safety guard before depressing the applicator mechanism. Firmly but gently deploy the sensor according to the instructions that came with your system. Carefully remove the applicator. Most applicator models will leave behind a transmitter holder. Leave that in place.
Attaching your transmitter
Open the transmitter packaging and do not touch the metal dots that conduct electronic communication between the sensor and the transmitter. Do not scratch the transmitter or otherwise damage the seal. Make sure you’re using the transmitter with the correct serial number.
Wipe the bottom of the transmitter with an alcohol wipe and allow it to aid dry. Attach the transmitter to the transmitter holder according to the instructions that came with your device. It should either slide or click into place.
When the sensor and transmitter are successfully connected, run your fingertip around the adhesive patch three times to secure it.
Pairing to the app
Keep the transmitter and smart device within 20 feet of each other with no obstacles – including water – around or between them. Make sure Bluetooth is on. Pairing can take up to 30 minutes. You can start the warm-up when you see the pairing confirmation screen. If you didn’t previously enter a code, you’ll be prompted to calibrate your system twice for the initial setup.
Pairing to the receiver
Turn on or wake up your receiver. Pairing should begin automatically. If not, follow the instructions that came with your CGM system to begin pairing. Wait for confirmation, then start the warm-up. During the two-hour warm-up, keep your receiver and transmitter within 20 feet of each other with no obstacles – including water – around or between them. You’d have to calibrate twice if you didn’t enter a code.
Calibration is when you enter a blood glucose meter reading into your app or receiver so that the software knows how to gauge the sugar level in your interstitial fluid. You don’t have to calibrate if your model allows a code, but you can if you want to. Follow the on-screen instructions for calibration if needed.
As an example, the calibration process for the Dexcom G6 is as follows:
Wash and dry hands
Take a fingerstick with your blood sugar meter
Calibrate twice after warm-up
Calibrate 12 hours later
Calibrate again 12 hours later
Calibrate 24 hours later and every 24 hours after that for the duration of the session
You’re now ready to use a CGM system! When your setup is complete, your CGM system will start taking and recording your glucose levels every five minutes, no matter what you’re doing, as long as the transmitter is attached and can communicate with the receiver. Some models can take and store data for a limited time when the connection is lost.
Calibrate your device any time your symptoms don’t match your readings. Always verify glucose levels with a blood glucose meter before deviating from your regular treatment plan. If your blood glucose reading differs from your CGM reading, base treatment decisions on your blood glucose reading and calibrate your CGM device.
Current levels, taken every five minutes day and night, are typically displayed in a circle on the main dashboard of your receiver or app. The Dexcom G6 and Libre 2 models have arrows that indicate the speed and direction of your glucose changes in real-time. The chart shows your target range and plots your readings over time so you can monitor trends.
When you enter an event, the system will incorporate that event into your trend data so that you can see how things like exercise and illness affect your glucose levels. Over time, that trend data will help you and your healthcare provider refine your treatment plan and keep you as healthy as possible. Events that you should enter while using a CGM system might include:
Alarms and alerts
Your CGM system will let you know when your glucose levels are out of range or if they’re climbing or dropping rapidly. You can customize alerts and alarms to an extent – some systems won’t allow you to disable warnings for hypoglycemic events.
Setting alerts allows you to verify with a blood glucose meter and take corrective action before you’re out of range and before you experience a dangerous glycemic event.
You’ll customize your alerts when you set up your app and receiver. Be cautious of headphones, Do Not Disturb settings, and other settings or functions that might silence your important alerts.
Sharing your CGM data
Sharing your glucose trends and data with your healthcare provider will help them optimize your treatment plan and keep you in range. To share your data, ensure your device is not in airplane mode and that you’re opted to send data to the cloud. Ensure both devices are charged, turned on, and connected to the internet. You can send data manually when needed or share your CGM data constantly throughout the day.
If you’re trying to share CGM data while talking on the phone, you’ll need to enable simultaneous voice and data transfer. Then follow the prompts on your app or receiver to add a recipient and share your data. In most cases, the recipient needs to have the data share app for your device before they can receive anything.
CGM sessions will end automatically and prompt you to start a new session. If you need to end a session manually because of sensor failure or other issues, find the sensor session options in your app.
When the session ends, peel the old adhesive up and away from your skin like a Band-Aid and remove the sensor. You’ll probably need to keep the transmitter. Dispose of your CGM blood-contaminated materials according to local regulations.
Talk to your healthcare provider before you start monitoring your glucose levels with a CGM system. Ask them:
When to use a meter instead of the CGM reading alone
How to avoid insulin stacking with CGM
What your target range should be
How to make treatment decisions based on CGM readings and alerts
What else you need to know before starting your CGM journey