What’s a CGM

September 29, 2018
Est. Reading: 3 minutes
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Continuous Glucose Monitor (CGM) makes information about glucose levels readily available to diabetics for treatment decisions. CGM devices are FDA-approved systems that automatically take readings at 5- to 15-minute intervals. What happens next can be life-changing.

Managing diabetes, or other conditions that require knowledge of glucose levels, can be a complicated matter. Carrying glucose monitors, test strips, and lancets as part of the daily kit get old – fast. Pricking your fingers to take readings twenty times a day or more when glucose levels are fluctuating widely can leave fingertips feeling like they will bleed on demand. For babies who cannot tell an adult how they feel and for kids who are active and focused on the game or the fun, there is often no clear signal that a severe and serious low is imminent. For adults who have a long history of diabetes, it is also very likely that they are no longer aware of the signs that should interrupt their activity or awaken them in the night.

Continuous Glucose Monitors (CGMs) make use of technology that provides a solution to the glucose-reading part of the problems by automatically taking readings every five to fifteen minutes and acting on those readings in a variety of ways. Some of these FDA-approved devices make those reading available to the person wearing the device and the people assigned to track those readings through their phones or receivers.

The Dexcom G6 is one such system. It does not just track “glucose levels.” It will also sound an alarm when levels are rising rapidly, falling rapidly, or approaching dangerously low levels. It’s also thrilling for diabetics because it does not require calibration with finger-prick glucose readings.

Other CGMs take the readings but do not provide readouts unless “asked.” They also do not provide alarms. They are read when a device is held near them. The FreeStyle Libre is one such device. Whether a device is needed and which is preferable depends upon the situation. 

CGMs, do not, as a matter of fact, record blood glucose levels. These devices are worn on the stomach, upper buttocks, arms, thigh, or another area of the body that has fat and muscle present. The fluid these measure is the interstitial fluid that surrounds tissue cells beneath the skin. This fluid results from glucose that moves from your blood vessels and capillaries first. As a result, the reading on the CGM rarely matches the readings on a glucose meter because they are measuring two different things.

There is generally about a fifteen minute lag between the blood-stick reading and the CGM reading, especially during a time when levels are rising or falling. Add to this the allowable margin for error of about 20% on both devices, and you see that trying to make a match is both impractical and frustrating.

The value of the CGM is that it is measuring a fluid that reflects the blood glucose levels because it is derived from those levels. The trends are the valuable part of the information recorded because they show what your glucose is doing – rising, falling, approaching a dangerously low level. They also allow people wearing these devices to see the way their bodies are reacting to their level of exertion and/or the foods they are choosing. After wearing a device for a few weeks, most people report they have been able to use their insulin in conjunction with the readings to make a meaningful change in their A1C.

~ gina


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