Understanding Continuous Glucose Monitoring
Did you know there are different ways to test and monitor your blood sugar? Glucose levels can be checked through different methods like a blood glucose meter and test strip or with a continuous glucose monitor, which uses a wearable sensor.
In this article, we dive into the specifics on continuous glucose monitoring, including:
- What is Continuous Glucose Monitoring?
- Who Should Use Continuous Glucose Monitoring?
- How Does Continuous Glucose Monitoring Work?
- How Much Does a Continuous Glucose Monitor Cost?
- Deciding if a Continuous Glucose Monitor is Right for You
- What the Future Holds for Continuous Glucose Monitoring Technology
What is Continuous Glucose Monitoring?
A continuous glucose monitor — often abbreviated as CGM — is a wearable sensor that automatically measures glucose levels 24 hours a day.
While a blood glucose meter measures the amount of glucose through a drop of blood on a test strip, a CGM measures the amount of glucose in your interstitial fluid (the fluid surrounding your cells) through a sensor placed just under your skin.
There are generally two types of sensor-based monitoring systems available:
- Continuous glucose monitoring (CGM), which provides glucose readings at specific intervals, such as every five minutes or so.
- Flash glucose monitoring (FGM), which displays a glucose reading every time the handheld reader is scanned over the sensor.
The amount of time that the CGM or FGM sensor is worn varies depending on the manufacturer. But the idea is that the sensor stays on the body for a week or more, before you insert a new one.
Who Should Use Continuous Glucose Monitoring?
According to the American Diabetes Association’s abridged 2019 Standards of Medical Care in Diabetes, monitoring blood glucose is key for achieving target blood glucose levels for most people with diabetes.
Traditionally, self-monitoring with a blood glucose meter is an effective way to understand and assess glucose levels. CGM is a complementary tool that can help people who test multiple times a day to understand additional context around their glucose changes from physical activity, foods, and the effect of medications like insulin.
Since a CGM is automatically capturing a glucose reading throughout the day, people who need to test frequently may find the most benefit from a CGM.
The National Institute of Diabetes and Digestive and Kidney Diseases notes that a CGM may be recommended if:
- You’re on intensive insulin therapy
- You have hypoglycemia unawareness
- You frequently have high or low blood glucose
CGMs require a doctor’s prescription and often approval by your insurance, so it may be helpful to check with your insurance plan for coverage details. The age ranges for CGM systems vary, but some systems are now approved for use in young children, ages two and up.
How Does Continuous Glucose Monitoring Work?
To understand how a CGM system works, you need to become familiar with the three main components: the sensor, transmitter, and receiver.
- Sensor: The sensor is a very thin wire or filament, inserted with the aid of a needle under your skin. A sensor is typically applied on your abdomen, the back of your arm, or other locations depending on the manufacturer’s recommendations. In order to hold the sensor in place, there’s usually a sticky backing, much like a band-aid, that attaches the sensor to your skin. Using similar enzymes as a test strip for a glucose meter, the sensor’s job is to detect glucose in the interstitial fluid, which is the fluid between the cells. Sensors can stay in place for several days, but the exact duration will depend on manufacturer’s specifications. Typically, the receiver or app that works with the system will alert you when it’s time to replace the sensor.
- Transmitter: The transmitter acts as the middleman between the sensor and the receiver. It attaches to the top of the area where the sensor was inserted. From there, it’s able to wirelessly send information to the receiver through radio waves. Some transmitters are rechargeable, while others do not require charging but need to be replaced every few months.
- Receiver/Monitor: The receiver’s job is to receive and display the information from the sensor. It has a screen where you can check your current glucose levels and view past readings. The receiver can also send you warnings if your glucose levels are too high or low, deliver status messages, and display trend information to help you understand how much your glucose level is going up or down over time. Some modern CGMs are Bluetooth®-enabled so they can send readings right to a smart device, like your mobile phone or tablet. The apps that work with CGMs have additional special features, including graphing, trends, and the ability to share glucose data with family or caretakers.
Flash Glucose Monitoring
FGMs work in a similar manner, except there are just two components: a sensor and a reader/monitor.
The FGM does not transmit data to the reader/monitor without action taken by the user to scan the sensor. Some people see this type of system as a middle ground between testing with a blood glucose meter (at one point in time), and the steady stream of data that comes from a CGM. Since the FGM currently does not transmit data to the reader/monitor without the scanning action, alerts for high or low glucose will only appear at the time you are scanning. However, trend information is displayed along with the glucose reading, in the form of a trend arrow and an eight-hour glucose history graph.
Limitations with CGM and FGM
While each of these systems enables an at-a-glance view of your glucose levels with less testing, there are still times when a fingerstick with a blood glucose meter may be needed. This includes:
- Multiple, daily blood glucose calibrations (varies by model)
- Before dosing insulin or making treatment decisions (varies by model)
- When CGM or FGM readings do not match symptoms
- During the initialization of a new sensor
- Times when a CGM or FGM cannot be worn, or when a technical issue prevents them from displaying a reading
If you’re looking to use either of these devices, it’s still important to make sure you also have a reliable and accurate blood glucose meter and test strips.
How Much Does a Continuous Glucose Monitor Cost?
Just like other diabetes supplies, pricing will vary from brand to brand, and your health insurance plan will determine what and how much is covered.
To regularly monitor your glucose with a CGM, there will be supplies like sensors and transmitters that need to be purchased on an ongoing basis, so it’s important to have plenty on hand.
Based on example pricing shared through one online source, testing with a CGM could be over $10/day if insurance offers little coverage, to $2-3/day if insurance covers more of the costs. FGM costs tend to be slightly lower, as most people in the U.S. with commercial insurance are estimated to pay a couple dollars a day.
The exact price you’re required to pay will depend on the amount and type of supplies you need, your health insurance coverage, and other factors.
Deciding if a Continuous Glucose Monitor is Right for You
Many of the benefits of a CGM were described above, including the convenience of having a small sensor that can give you glucose readings as you go about your normal activities, including eating, sleeping, exercising, showering, etc.
Depending on the model, it can also give you an advanced warning of when your glucose may drop dangerously low (called hypoglycemia) or alert you when glucose levels are trending low or high. Many people find it helpful to see how their glucose levels vary throughout the day without having to remember to test or prick their finger. A CGM may also be able to work in conjunction with an insulin pump, providing additional insulin and glucose management features.
Drawbacks of a CGM may involve the insertion, visibility, and maintenance of a sensor. Because of the technical nature of the system, it helps to be tech-savvy although your healthcare provider may offer some initial training. Some people have no issues or pain attaching a sensor while others may find it a bit cumbersome with some discomfort. Since the sensor uses adhesive to remain attached to the skin, it’s possible to experience skin reactions or have trouble keeping the sensor adhered.
For those looking for a safety net to catch excursions in glucose levels, such as undetected low glucose, the CGM will sound an audible alert, while a FGM system will not give an alert or share this data in real-time with family.
You may also notice a 15-20 minute lag time, or difference in the glucose levels when measured through a blood glucose test with a meter versus interstitial fluid with a sensor. If you feel symptoms of high or low glucose, but your sensor gives you an in-range reading, you should confirm with a test from a blood glucose meter.
Lastly, the financial cost for CGM or FGM supplies can potentially be expensive, and not all insurance providers cover the cost.
What the Future Holds for Continuous Glucose Monitoring Technology
It’s an exciting time for diabetes tech innovation as CGM functionality continues to evolve and new CGM manufacturers enter the market. There are also further developments and research into the connection between a CGM and insulin pump, and ways to automate the insulin delivery process.
For CGMs, researchers are hoping to develop longer lasting sensors and further smartphone connectivity and features. To learn more, Diabetes Forecast offers a rundown on some next generation diabetes products on the horizon.
If you have any questions about continuous glucose monitoring or blood glucose meter technology, please contact us here.