A CGM or flash monitor is made up of:
- a sensor – a small device you attach to your arm or tummy that senses how much glucose is in the fluid under your skin, called interstitial fluid
- a reader or receiver, which shows the results (you can also get the results on your smartphone, if you have one)
With CGM, the sensor sends results to the receiver or your phone every few minutes. You can see your glucose levels on your receiver at any time. Some types can send results to an insulin pump, so you can see your glucose levels on your pump.
With flash, you need to scan the sensor with the reader or with your phone to see the results.
There are several different types of CGM. The only type of flash monitor available is the Abbott FreeStyle Libre 2. The original Abbott FreeStyle Libre has been discontinued.
Some types of CGM have optional alarms to alert you if your blood glucose levels go too low or too high. The Abbott FreeStyle Libre 2 also has an alarm.
You generally need to replace a sensor every 7 to 14 days, depending on the type of monitor you have.
Interstitial fluid glucose readings are a few minutes behind your blood glucose levels. This means you’ll still need to do finger-prick checks every now and then, particularly when you drive or have a hypo.
To get the best out of CGM or flash, you’ll need to look at the information it gives you with your team.
Getting CGM or flash on the NHS
CGM or flash glucose monitoring should be available on the NHS to anyone with type 1 diabetes.
Children and young people will usually be offered CGM. Adults will usually be offered a choice of CGM or flash.
Ask your diabetes team about getting CGM or flash glucose monitoring.
What is continuous glucose monitoring?
Continuous glucose monitoring means using a device to automatically estimate your blood glucose level, also called blood sugar, throughout the day and night. You can see what your blood glucose level is at any time. You can also review how your blood glucose level changes over a few hours or days and spot trends.
Seeing your blood glucose levels in real time can help you make more informed decisions about the food and beverages you consume, the physical activity you do, and the medicines you take. Keeping your blood glucose level in your target range can help prevent other health problems caused by diabetes.
How does a continuous glucose monitor work?
A continuous glucose monitor (CGM) estimates what your glucose level is every few minutes and keeps track of it over time.
A CGM has three parts. First, there is a tiny sensor that can be inserted under your skin, often the skin on your belly or arm, with a sticky patch that helps it stay there. These sensors are called disposable sensors. Another type of CGM sensor—called an implantable sensor—may be placed inside your body. CGM sensors estimate the glucose level in the fluid between your cells, which is very similar to the glucose level in your blood. Sensors must be replaced at specific times, such as every few weeks, depending on the type of sensor you have.
The second part of the CGM is a transmitter. The transmitter sends the information, without using wires, to the third part, a software program that is stored on a smartphone, on an insulin pump, or on a separate device called a receiver.Most CGMs send information without using wires to an app on a smartphone.
Who can use a continuous glucose monitor?
Your doctor may recommend that you use a CGM if you need insulin to manage type 1 diabetes, type 2 diabetes, or another form of diabetes. Talk with your doctor about whether using a CGM could help you manage your diabetes.
Doctors can prescribe CGMs for adults and children. Some models can be used for children as young as 2 years old.
Your doctor may suggest using a CGM all the time or only for a few days to help adjust your diabetes care.
What are the different types of continuous glucose monitors?
All CGMs estimate blood glucose levels, but they store and display the information in different ways.
Some CGMs send and display information to your smartphone or receiver automatically. These CGMs are called “real-time” CGM devices. Another type of CGM, called “intermittent-scan,” estimates glucose levels continuously. But you will need to scan the CGM with a separate receiver or smartphone every few hours to view and store the data. A third type of CGM collects data about your blood glucose level for your doctor to download and review later. Doctors provide this type of CGM to check on your diabetes care, and you wear it for a limited time.
Other differences between CGM models include
- whether the sensor is placed on the skin or is implanted
- how often the sensor has to be replaced
- how long it takes the CGM to warm up
- how you adjust the program settings
For some CGM models, you may need to do a finger-stick test with a standard blood glucose monitor to calibrate the system and make sure the CGM readings are correct.
What are some features of continuous glucose monitors?
When worn, CGMs are always on and recording glucose levels—whether you’re showering, working, exercising, or sleeping. Many CGMs work with apps that have special features, such as
- ways to track the food and beverages you consume, your physical activity level, and the medicines you take
- the ability to download data onto a computer or smart device so you can easily see trends in your glucose levels
- an alarm that goes off when your glucose level is too low or too high, helping you prevent emergencies
For safety, it is important to act quickly if a CGM alarm sounds when your glucose level is too low or too high. You should get help or follow your treatment plan to bring your glucose level into a healthy range. Some CGM models can also send information to a second person’s smartphone—such as a parent, partner, or caregiver. For example, if a child’s glucose level drops dangerously low overnight, the CGM could be set to wake a parent in the next room.
What are the benefits of a continuous glucose monitor?
Compared with a standard blood glucose meter, using a CGM can help you
- better manage your glucose levels every day
- have fewer low blood glucose emergencies
- need fewer finger sticks
The CGM will create an alert and might display a graphic that shows whether your glucose level is rising or dropping—and how quickly—so you can choose the best way to reach your target range.
Over time, keeping your glucose levels in the healthy range can help you stay well and prevent diabetes complications. The people who benefit the most from a CGM are those who use it every day or nearly every day.
What issues could you have while using a continuous glucose monitor?
Researchers are working to make CGMs more accurate and easier to use. However, you may experience some issues while using a CGM.
For safety, you may sometimes need to compare your CGM glucose readings with a finger-stick test and a standard blood glucose meter. This could be needed if you doubt the accuracy of your CGM readings, if you are changing your insulin dose, or if your CGM gives a warning alert.1
You might have to replace parts of your CGM over time. Disposable CGM sensors should be replaced every 7 to 14 days, depending on the model. Some implantable sensors can last up to 180 days. You may have to replace the transmitters of some CGMs. You may also need to reconnect the CGM, transmitter, and receiver or smartphone if your CGM is not working correctly.
Skin redness or irritation from the sticky patches used to attach the sensor may occur for some people.1 Your doctor can suggest techniques or medicines to help relieve skin problems.
A CGM costs more than using a standard glucose meter, but it may be covered by your health insurance. You might be able to get financial help for diabetes care from your health insurance or other resources. Check with your health insurance plan or Medicare External link to see if the costs will be covered.For safety, you may sometimes need to compare your CGM glucose readings with a finger-stick test and a standard blood glucose meter.