If you have difficult to control diabetes on insulin therapy—or if you’ve had troublesome drops in blood glucose—your doctor may have suggested using a continuous glucose monitor. This monitor can reveal minute-to-minute fluctuations in blood glucose.
While anyone with diabetes can benefit from the information that CGMs can reveal, they are expensive devices so insurance companies may not always pay for them. In general, they are considered most appropriate for:
Besides the convenience of not having to prick your finger, a CGM gives you insights into how your metabolism is functioning that were previously impossible to know. You can see what happens to your blood glucose levels while you are asleep (in some people, they drop a lot lower than they ever realized). You can see how long it takes after you eat for your glucose to spike, what the maximum glucose is after the meal, and how long it takes to return to baseline. You can see how different foods spike your blood sugar level, giving you great biofeedback that will help you make healthier choices. With a CGM, you can generate reports that give great detail about your blood sugar control that go beyond what you learn from an A1C test (see image below). A new statistic invented since the advent of CGMs, called time in range, many eventually replace the A1C as the most important metric for assessing how well diabetes is being controlled.
These monitors are attached to a small sensor placed beneath the skin of the person’s abdomen, arm, or upper buttocks. On top of the skin sits a transmitter, which relays information to a wireless receiver.
Every 5 minutes, the sensor measures the glucose level of the tissue just beneath the skin . The transmitter sends the reading to a hand-held device known as a receiver. Nowadays, your cellphone can serve as the receiver (though dedicated receivers are still made). You can see the results on the receiver’s screen, and download the information.
The monitors provide a huge amount of information but this information reflects the amount of glucose in the fluid just under the skin, rather than the amount of glucose in the blood. As a result, this means that the results are not as accurate as fingerstick glucose meters, and there can be a small lag in the continuous glucose monitor readings. Some CGMs need to be calibrated with results from a finger stick glucose reading multiple times throughout the day. However, a some of the newer CGMs do not require fingerstick blood glucose calibration.
Currently available CGMs as of 2020
“Flash” or intermittent CGMs provide readings on demand by waving a receiver over a sensor that is usually worn on the arm. This type of device is not quite as advanced as those mentioned above (since you have to scan the device to get the reading). However, the advantage of of this type of CGM is that it is much less expensive, and even without insurance can be purchased for about $75 a month. There is only one flash CGM, and it’s called the Freestyle Libre.
A device called Eversense is now available that is implanted under the skin on the back of your arm. The implantation is a quick procedure done in your doctor’s office, and it has to be changed out every 90 days. It is expected that this device will eventually be able to be implanted for up to a year at a time in the future, but this is still in development.