Is Continuous Glucose Monitoring for You?

The medical field is always searching for innovative ways to improve the lives of patients. When it comes to advancing diabetes care, there is no question that continuous glucose monitoring is one of the major developments in the last two decades.

From the early 1900s to the mid-1960s, the only option for blood sugar monitoring for people with diabetes was to test their urine for sugar. This method was less than ideal, to say the least, as it involved either heating up the urine or adding a reagent tablet (similar to an Alka-Seltzer) to the urine. Patients would then watch the color change and match this to a chart showing if the sugar was high or low.

In the 1960s, a fingerstick test for blood sugar became available, but only for use in a physician’s office. It was not until the 1980s that home blood sugar meters came to market, allowing people the ability to more accurately and more easily check their blood sugars at home. Blood sugar testing daily or multiple times a day (depending on the type of diabetes) became the standard of care.

The scientific community did not stop there, as they knew a fingerstick glucose reading represented only a point in time and did not tell the whole story. In the early 2000s, the first continuous glucose monitor, or CGM, came to market. By 2016, the accuracy of these sensors was so good that the U.S. Food and Drug Administration (FDA) approved continuous glucose readings to replace fingerstick blood sugar testing altogether.

CGMs are small devices worn on the body, typically on the abdomen or back of the arm, that monitor the interstitial glucose every 1 to 5 minutes. To understand interstitial glucose, think about a blood vessel underneath the skin. The vessel is surrounded by fluid called the interstitium. When sugar is in the bloodstream, it moves from the blood vessel into the interstitial fluid, where it is detected by a tiny sensor (see the diagram below). The sensor sends the reading to the glucose monitor’s transmitter, which then sends it to the patient’s receiver or their smartphone.

With CGM, people living with diabetes always know what their blood sugar is. There are also features on the device that tell the patient if their blood sugar is trending high or if they are headed for a dangerously low sugar. Alarms can be set to alert the person to these events so they can make informed decisions. For example, if the person’s blood sugar hits 70 mg/dL or less, an alarm will go off so that the person knows to eat or drink a small amount of sugar before they drop any lower.

Everyone! Data support the use of CGM for essentially everyone with diabetes—including type 1 and type 2 as well as prediabetes. CGM is even being studied in people without diabetes, such as athletes.

If you have type 2 diabetes, even without needing insulin, CGM can be very beneficial. With these devices, for the first time in history people really understand how their body responds to what they eat. If you eat a doughnut, you can look directly at your smartphone and watch the blood sugar spike. This can lead to major lifestyle changes for individuals living with diabetes.

In general, CGMs are covered by commercial insurance plans for people with diabetes. Medicare and Medicaid have continued to expand coverage of CGMs based on how compelling the data is to support their use in improving diabetes management and reducing potentially life-threatening low blood sugar events. If you are not sure whether CGM will be covered, check with your plan.

The table below gives a comparison of some of the available CGMs in the U.S.

Calibration refers to whether the device needs to be reset with periodic fingerstick blood sugar measurements. Some models require this and some do not. For instance, with Medtronic Guardian 3, the patient needs to check fingerstick sugars two to three times per day, whereas Dexcom G6 and Freestyle Libre sensors do not require this.

The mean absolute relative difference (MARD) is a number indicating how accurate the sensor is as a percentage. The lower the MARD, the more accurate the sensor. In general, a CGM company needs to show a MARD less than 10% for the device to be approved.

CGMs all have variable wear times after which the sensor needs to be changed. These vary from seven days up to six months (in the case of the Eversense E3, which is implanted underneath the skin every six months.) All can be changed yourself except the Eversense, which is changed in a physician’s office.

Interfering substances refers to medications or substances that could interfere with the performance of the sensor.

Unique features of each model are included in the table. For example, Dexcom G6 communicates with Tandem and Omnipod insulin pumps to form hybrid closed loop insulin delivery systems. Libre 3 is tiny, the size of a penny, and unlike previous versions does not require any scanning for the blood sugar reading to appear. Medtronic Guardian 3 talks to its own insulin pump. Eversense E3 is implantable.

One of the best features shared by all the CGMs is the ability to share your blood sugar data with friends, family, and physician offices. You could be on the East Coast and your loved one on the West Coast, and they could simply look at their smartphone to see your blood sugar readings.