My Take on the Continuous Glucose Monitor

A few months ago while talking to my diabetes educator about my difficulties tracking nighttime trends, she mentioned the words "continuous glucose monitor". Most diabetics rely on multiple daily blood sugar tests, but for an increasing number, continuous glucose monitors supplement blood sugar test to provide a more accurate picture of blood sugar trends.

Continuous glucose monitor systems, which I'll call from now on CGMS, measure the glucose levels of subcutaneous (under-the-skin) tissue and automatically convert these numbers their blood sugar equivalents. The sensor is inserted just like an insulin pump canula, and takes a glucose reading every 10 seconds. The average 5-minute blood sugar equivalent is transmitted to a pager-sized "monitor", which displays graphs of blood sugar trends over various time increments ranging from 1 hour to 24 hoursdepending on the CGMS model. 

There are currently four FDA-approved CGMS: two produced by Medtronic, and one each from Dexcom and Abbott. According to the FDA, the sensor should be changedMinimed Guardian CGMS every three to seven days, depending on the model. Additionally, users must calibrate (enter a finger test blood sugar reading into the monitor) the sensor once every six to 12 hours depending on the model.

No matter which sensor you choose, you cannot take insulin or treat lows based on sensor readings. In other words, sensors are helpful in identifying long-term trends, such as nighttime blood sugars and post-meal spikes, but not accurate enough to program into your pump to take insulin for food.

My diabetes educator was clear with me about the purpose of CGMS: they do not replace manual blood sugar tests, and for many, do not even reduce the number of daily blood sugar tests. I have found, however, that the innovative 24-hour blood sugar graph provides trends that help me in both the long-term and short term.

In the short term, I use the CGMS' information to prepare myself for exercise. Next to the blood sugar graph, the sensor displays arrows indicating if the blood sugar is falling, rising, or staying steady. Before I exercise, I'll wait 15 minutes or have an extra snack if my CGMS tells me my blood sugar is 120 and falling.

In the long term, I can compare trends in my blood sugar to see if I need to change my doses. For example, if one day my blood sugar climbs from 70 to 140 within two hours and the next day from 130 to 200 during the same time increment, even though the ending blood sugars are different, I'll be able to recognize that I might need to examine my dosages.

In addition, my CGMS reminds me not to neglect my diabetes care. A 24/7 blood sugar graph is great incentive to keep on top of my carb-counting and testing.

Lastly, CGMS can be programmed to alert users to high and low blood sugar. However, the sensor readings are about 20 minutes behind actual blood sugar readings, so by the time the sensor alerts users to a blood sugar of 65, he or she had already reached for the glucose tabs. As I've said before, the CGMS is more useful in identifying trends.