Continuous Glucose Monitoring: What You Need to Know

Continuous glucose monitors (CGMs) are revolutionizing the way people manage their diabetes. Learn more about how these devices work, if your insurance covers CGMs, and how integrating one into your diabetes management routine can improve your foot health.

What Is a CGM and How Does It Work?

A continuous glucose monitor is a wearable medical device that measures the sugar levels in your body every 5-15 minutes. The data is sent automatically to a reading device, like a smartphone or insulin pump, which allows you to check your glucose levels at any time during the day or night without a finger-stick.

CGMs are made up of three components:

• Sensor: The portion of the device that sits under the skin and measures glucose levels.
• Transmitter: Attaches to the sensor and sends the measurement data to the receiving device.
• Reader: A receiving device with a display that allows you to see your glucose measurements in real-time.

Unlike blood glucose monitors, CGMs work by measuring the levels of glucose in body fluid, known as interstitial fluid, rather than blood. You or your doctor will insert the small sensor just under the skin on your belly or arm, where it will take measurements every few minutes.

The sensor is attached to a transmitting device, which will wirelessly send measurements to a smartphone or other handheld receiver so you can instantly see your glucose level.  

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Who Can Benefit From a CGM?

CGMs were initially designed to reduce significant blood sugar fluctuations in people with Type 1 diabetes. In recent years, those with severe Type 2 diabetes have benefited from the convenience of CGMs, and they are becoming a more common tool in the management of this disease.

A prescription from a healthcare provider is needed to get a CGM. Your doctor might recommend a CGM if:

• You have a narrow target blood sugar range
• You do not easily recognize the symptoms of hypoglycemia
• You frequently experience very high or very low blood sugar

How Can CGMs Help Improve Foot Health?

When used correctly and under the guidance of a healthcare professional, CGMs can help people with diabetes keep their blood sugar within a safe target range. Each person’s target range will vary based on their doctor’s recommendations, but staying within this range as much as possible can reduce the risk of developing new or worsening diabetic neuropathy and peripheral artery disease.

Time-in-range (TIR) is the percentage of time someone with diabetes keeps their blood sugar within the parameters set by their doctor. This measurement is calculated by dividing the number of glucose levels within target range by the total number of glucose checks and multiplying by 100. Most CGMs will do this calculation automatically using 14 days of stored data.

# of glucose measurements in range# of total glucose checks100 = Time in range

TIR is a great way to gather data about your glucose management over time, and it is more sensitive than an A1C test. While an A1C determines your average blood sugar over two to three months, it does not offer information about the amount of time spent in the high, low, or target glucose range.

Although TIR is a relatively new measurement since the introduction of CGMs, recent research indicates that a higher TIR is associated with fewer diabetic complications.

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Different Types of CGMs

In the United States, several different CGM devices are available on the market. Which one is right for you will depend on the severity of your diabetes, your doctor’s recommendations, and your insurance coverage.

The two types of CGMs are real-time monitors and intermittently scanned monitors. They each perform the same function, but how you receive the glucose measurements will vary.

Real-time monitors will continually send measurement data to your receiver, allowing you to simply pick up the device and see your stored glucose data at any time. These devices have the added benefit of alerting you of high or low glucose readings, which can help prevent emergencies and give you extra peace of mind.

Intermittently scanned CGMs will only send measurement data to your receiver when you tell it to, usually by waving your receiving device over the transmitter. These devices are convenient, easy to use, and affordable, but they do have limitations:

• They do not send alerts for high or low glucose readings.
• The user needs to remember to transmit data, or it will be lost after 8 hours.

Each CGM device will have slightly different care instructions, like how frequently the sensor should be changed, if the device requires calibration with finger-stick glucose, and how long the sensor needs to warm up before it can begin taking measurements.

We recommend referring to this table to compare the functions and limitations of each device currently available in the US.

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Insurance Coverage

CGMs are great tools for managing diabetes, but they can be quite expensive. Luckily, most private insurance companies will cover CGMs for qualifying individuals, but they may only cover certain brands. It is important to check with your insurance company before purchasing a CGM to ensure the device and supplies (sensors and transmitters) are covered.

Many CGM companies have financial assistance programs in place to help reduce out-of-pocket costs for these devices.

As of August 2021, Medicare offers CGM coverage for both Type 1 and Type 2 diabetics who meet the following qualifications:

• Has diabetes mellitus
• Is treated with three or more daily administrations of insulin or a continuous subcutaneous insulin infusion (CSII) pump
• The insulin treatment regimen requires frequent adjustment based on blood glucose results.

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Additional Sources

Beck, R., et al. Validation of Time in Range as an Outcome Measure for Diabetes Clinical Trials. Diabetes Care. Published March 1, 2019

Cleveland Clinic. Continuous Glucose Monitoring. Reviewed August 7, 2021.