What Is Continuous Glucose Monitoring?
Continuous glucose monitoring, or CGM, has changed diabetes care for many people. Instead of a single reading from a finger prick, a CGM provides a stream of readings around the clock and shows which direction glucose is heading. Here is how it works and what to consider.
Key points
- A CGM measures glucose in the fluid under the skin every few minutes through a small wearable sensor.
- It shows trends and can alert you to highs and lows, including overnight.
- CGMs are usually prescribed, and a standard meter is still useful as a backup.
How a CGM works
A CGM has three parts.
- A sensor: a tiny filament inserted just under the skin, usually on the abdomen or upper arm, held in place by an adhesive patch. It measures glucose in the interstitial fluid, the fluid between cells.
- A transmitter: sends the readings wirelessly.
- A receiver: a dedicated device, a smartphone app or an insulin pump that displays the data.
Disposable sensors are worn for a set period, typically one to two weeks depending on the model, and then replaced. One type of sensor is implanted under the skin by a healthcare professional and lasts for months.
Types of CGM
The NIDDK describes three kinds:
- Real-time CGMs send readings to your device automatically and continuously.
- Intermittent-scan CGMs record continuously, but you scan the sensor with a reader or phone to see the result.
- Professional CGMs are fitted by a clinic for a limited period; your doctor then reviews the data with you.
What a CGM shows you
- Your current glucose level
- A trend arrow showing whether it is rising, falling or steady
- A graph of the past hours
- Alerts when levels go too high or too low
- Summary reports, including “time in range”, the percentage of time glucose stays within your target range
Benefits
According to the NIDDK, compared with a standard meter a CGM can help you:
- manage daily glucose levels better;
- have fewer low blood sugar emergencies;
- need fewer finger sticks.
Seeing the effect of meals, exercise and sleep in real time also helps many people understand their own patterns. Data can be shared with family members or a healthcare team.
Limitations
- Lag: interstitial fluid glucose trails behind blood glucose by several minutes, most noticeably when levels are changing quickly.
- Confirmation: you may need a finger-prick test to confirm readings, for example when symptoms do not match the display or as the instructions direct.
- Cost: CGMs cost more than standard meters, and insurance coverage varies.
- Skin reactions: adhesive can cause redness or irritation.
- Information overload: frequent alerts can be tiring; settings can be adjusted with your team.
- Interference: some medicines and supplements can affect certain sensors. Check the device instructions.
Who uses a CGM
CGMs are most often recommended for people who use insulin, including people with type 1 diabetes and some with type 2 diabetes. Your doctor may also suggest one if you have frequent or unrecognized low blood sugar. Most CGMs require a prescription, and your healthcare team will train you to insert the sensor, set alerts and interpret the reports.
CGM and insulin pumps
Some CGMs connect to insulin pumps. In automated insulin delivery systems, the pump adjusts insulin based on CGM readings. These systems still need input from the user, such as carbohydrate amounts at meals.
Why a meter still matters
Keep a standard meter and in-date strips available:
- as a backup if the sensor fails or falls off;
- during the warm-up period of a new sensor;
- when readings and symptoms disagree.
Our Blood Glucose Monitoring Kit is a compact backup option, with matching Blood Glucose Test Strips.
Questions for your healthcare team
- Would a CGM improve my management?
- Which type suits my treatment?
- Is it covered by my insurance?
- When should I confirm with a finger-prick test?
The bottom line
A CGM replaces snapshots with a continuous picture and can warn you before problems develop. It is a prescription decision to make with your team. See backup testing supplies in our diabetes care range.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases. Continuous Glucose Monitoring.
- American Diabetes Association. Devices & Technology.
- Centers for Disease Control and Prevention. Monitoring Your Blood Sugar.
More diabetes care guides
Understanding Blood Glucose Monitoring
Blood glucose monitoring shows how food, activity and medicines affect blood sugar. Learn how it works, the main methods and what results are for.
A Beginner’s Guide to Diabetes Care
Newly diagnosed or supporting someone with diabetes? Learn the basics: what diabetes is, daily self-care, monitoring, checkups and useful supplies.
Understanding the Importance of Diabetes Checkups
Regular checkups catch diabetes complications early. See the CDC care schedule: A1C, blood pressure, cholesterol, kidney, eye, foot and dental checks.