CGMS - What is it?

Ask our CDE

CGMS - What is it?


I keep hearing about CGMS.  First, what does this stand for? Secondly, how does it work?


CGMS stands for  "Continuous Glucose Monitoring System."  CGMS or continuous monitoring of your blood sugar is made possible by a “sensor“ placed subcutaneously (under your skin) in the interstitial tissue. This is done with a needle and an insertion device. The needle is removed and the sensor is left inside the interstitial tissue. These systems have three components, a sensor which is similar to an infusion set for pumps, a transmitter which is attached to the sensor and a receiver which receives the data (your blood sugars) wirelessly from the transmitter.The benefit of continuous glucose monitoring systems is to provide us with more data than ever before. If you currently check your blood sugar 4 times per day, you may think that is a lot but in the whole picture of a 24 hour day, it is not much information.

The CGM systems provide a blood sugar every 5 minutes or with one system, every minute. That is a lot of numbers and may really help you to evaluate what is going on and certainly helps your healthcare provider to see where you may need adjustments to your regimen. Another benefit is that this system allows you to set alerts to let you know if your blood glucose is getting too low or too high. I have seen a lot of people in our practice who no longer feel their low blood sugars. This can obviously be dangerous if you are low and are getting ready to drive yourself somewhere in your car. Some of my patients have had their driver’s licenses taken away because of accidents they have had because of low blood sugar. It would be difficult to stick your finger every 5 minutes to get that much data. That being said, it is important to understand that CGM systems DO NOT take away the need for fingersticks. If you get an alarm letting you know your glucose is high or low you have to confirm it with a fingerstick. These systems again represent sugar levels in our interstitial tissue which is not exactly the same as the fingerstick blood. There is a “lag” time. It may be 10-20%. You cannot expect to get the exact same number every time from your meter and the CGM. But it is helpful with trends over time. Also with all the systems currently available, you have to calibrate the devices with a fingerstick. So again, these systems rely on fingersticks and do not take away the need to check your blood sugar. The other issue to keep in mind is that this is fairly new technology and it should only get better with time. For those of you that are old enough, remember the first blood sugar meters? They were huge and took a lot of blood and at least 2 minutes to get a result. Now our meters take tiny amounts of blood and we get results in seconds. These systems too will improve with time. Also currently, a lot of insurance companies are not paying for these systems. They cost roughly $1000.00 for the “starter “kit and anywhere from $200-$300 per month for supplies. As with the first blood glucose monitors, this should change with time as well.

There are currently 3 systems available on the market. They are the Medtronic “Real time” MiniLink which goes with or is used in conjunction with the Medtronic pump or the Guardian which is for individuals not using pump therapy, The Dexcom “7” by Dexcom and the Navigator by Abbot. These products have been on the market for different lengths of time but no more than approximately 2 years. You can see what each system looks like by either pulling up the company’s website or googling continuous glucose monitoring systems. I have worn all 3 and even at least 2 at a time for comparison and for presentations. Talk about feeling like a bionic woman with a pump on and two other things attached to me! So that is the first thing to think about. These systems are attached to you and you wear them 24/7 for the life of the sensor which is anywhere from 3 -7 days.  Each system has some type of insertion device to get the sensor into your interstitial tissue. Then there is an initiation time where the sensor is finding its home in your interstitial tissue. This means that you do not get any data for a period of 2 -10 hours depending on the system.  Also the companies will tell you that the first 24 hours are unstable as far as the BG numbers go. Again, confirm numbers with a fingerstick. Once the initiation period is over, you should start getting numbers on the receiver which look like a cell phone or pager and can be kept in a pocket or a purse, most need to be within 6 feet from you.

In general, the pros to these systems are the amount of data we get. The ability to see what is going blood sugar wise for so many hours and see where adjustments are needed. And the alerts that can tell us if our blood sugars are headed down or up, so that we are able to take corrective action. If you are getting fairly reliable data, it can decrease the number of times you need to fingerstick. I must say it is pretty cool to be able to push a button and see what my BG is at any time! The cons are (1) that currently not all insurance companies are paying for them, (2) it’s another “thing” attached to you, and (3) the numbers may be “off” greater than 10-20% which can be hugely frustrating!! I think the good news with all of this is that technology is just getting better and improving our lives living with diabetes. The future is bright!