A continuous glucose monitoring system, or CGM, is part of the new “cutting edge” treatment options for patients with diabetes.

A CGM is an FDA-approved device that records a series of blood glucose readings throughout the day. These devices can provide up to 300 blood glucose readings in a day for three to seven days at a time, depending on the type of CGM you are using. 

The wonderful thing about CGMs is that they can be a useful tool to help troubleshoot blood sugar fluctuations that cannot be found with just routine finger stick monitoring. You don’t want to do a finger stick every five minutes, but your CGM can get readings continuously without skipping a beat. 

Sound easy? Well, not so fast, there is some preparation involved if you or your healthcare team decide that using a CGM would be best for you.

The important thing about using a CGM is to remember that these devices are not a “connect and go” solution. They require work on the part of the patient to make sure that they are being used correctly.

To avoid frustration, remember to learn all you can about any treatment plan before you start it. Your healthcare team can provide training, and may often include professionals that work with the company that makes your CGM. Pay careful attention to these sessions and always keep the customer service number for your new device close at hand in case you encounter a problem!

First, you will see that CGMs have a sensor electrode that gets inserted in the skin similar to how an insulin pump is used. Typically, these sensors are inserted into fatty areas such as the abdomen, buttocks, thighs, lower back, or arms. Most people use the abdomen because it seems to be the most comfortable spot. You want to avoid using the same spot too often to avoid irritation, and avoid areas of the body that you may bend a lot and irritate your site.

All CGMs require calibration with finger stick blood sugars at various intervals. This is to make sure your monitor is providing you with the most accurate results possible.

For example, the DexCom Seven requires calibration two hours after activation, and every twelve hours thereafter. The FreeStyle Navigator needs calibration ten hours after activation and every one to three days thereafter.  New models are being introduced into the market, so make sure you check the instructions specifically for your brand of CGM. Most manufacturers will advise you to calibrate your CGM at times when blood sugars are not fluctuating rapidly, such as right after eating or after brisk exercise for example.  

It is also important to note that sensor reading are generally supposed to be within 20 percent of finger stick values. They are NOT expected to be identical! This is because the sensor is reading interstitial fluid and your blood glucose meter reads blood plasma. The interstitial readings sometimes lag behind your finger stick readings a bit. The CGM is not totally replacing finger sticks, it is helping to identify trends so that you can get a better handle on possible problem areas, such as hypoglycemia during sleep, etc.