The Case for Continuous Glucose Monitors

Every time I attend my group meetings with my endocrinologist, there is always at least one patient who is hesitant to get on a continuous glucose monitor. Approximately four years ago, I too was one of those patients. The last thing I wanted was another device to have to carry around, another insertion site to make me look even more like a cyborg in my bikini, another beeping vibrating thing to draw attention to me in class. I stayed away for years for many of these reasons, and from what I have gathered during these group sessions, many other woman hesitate to invest in one for some of the same reasons. Four years with the Dexcom G4 has made managing my diabetes much easier, and now I can’t imagine living without it, but there still are some drawbacks. In this post I’ll take you through the benefits and limitations as well as guide you in how to effectively utilize some of the features the Dexcom comes with.

I use the Animas vibe, which combines the Dexcom G4 with the Animas Pump

Continuous Glucose Monitoring

Continuous glucose monitoring has changed the face of type 1 diabetes management. If you haven’t heard of the CGM (continuous glucose monitor), you may want to contact your endocrinologist as these are worth researching. Used well the CGM has the potential to help type ones gain tighter control over their blood glucose levels and even lower their hemoglobin A1c.

The CGM provides type 1 diabetics with the ability to monitor their blood sugars in real time. Rather than only gathering a limited number of blood sugars a day, the CGM gathers thousands of data points, updating continuously to a device (cell phone, receiver, insulin pump depending on which CGM model/company).   This allows an individual to more easily identify hypers and hypos and treat earlier, hopefully preventing extreme peaks in blood glucose.

Better yet, not only does this technology provide patients with their blood glucose in real time, but they also display trend arrows, which allow patients to view the direction in which blood glucose is trending. These arrows describe a rate of change and provide three different arrows/rates of change, allowing for more tailored treatment.

Individuals are even able to program their alerts through their device and tailor it to their own needs. For example, I set my high alert at 160 and my low alert at 80, which I find helps keep me in range, without driving me insane.

Here’s how to understand these arrows. Note that this is only for the Dexcom G5. This differs for other continuous glucose monitors.

Trend Arrows Dexcom Translation
BG not increasing or decreasing >1 mg/dL per minute
BG increasing 1-2 mg/dL per minute
BG increasing 2-3 mg/dL per minute
BG increasing >3 mg/dL per minute
BG decreasing 1-2 mg/dL per minute
BG decreasing 2-3 mg/dL per minute
BG decreasing >3 mg/dL per minute

Note: Arrows are based on average rate of change over the preceding 20-30 minutes

* Adapted from:

Pettus J, Edelman S. Recommendations for Using Real-Time Continuous Glucose Monitoring (rtCGM) Data for Insulin Adjustments in Type I Diabetes. Journal of Diabetes Science and Tecnology. 2016

Examining the Human Factor

Although these are great tools, they don’t quite take the human factor out of the equation. Currently, Minimed’s 670G hybrid closed loop insulin pump and accurate Guardian CGM, is the only FDA approved device that removes the human element. It is expected to be available in the spring of 2017. Until bionic pancreases take over the diabetes market, most of us need methods to correct and bolus utilizing these trend arrows on our CGMs.

A recent article written by Jeremy Pettus, MD and Steven Edelman, MD provides just the guide we need for effectively using those CGM arrows.

Here’s a basic summary of their suggestion for adjusting dosing utilizing trend arrows:

No adjustment.   Calculate for current BG level.
Add 50 mg/dl to current value and calculate correction
Add 75 mg/dl to current value and correct
Add 100 mg/dl to current value and correct
Subtract 50 mg/dl from current value
Subtract 75 mg/dl from current value
Subtract 100 mg/dl from current value

Now, as is pointed out in the paper, there are other factors to take into consideration including:

  1. Active insulin: when was your last dose? How long will it last? When will it peak?
  2. Meals: When did you last eat? What did you eat? Was it high in fat? How big was the portion?
  3. Exercise both prior and anticipated: What kind of exercise (aerobic, anaerobic, endurance)? Duration?
  4. Other medications that may raise blood glucose.
  5. Stress level: Stress can cause increased insulin resistance.
  6. Illness/infections: can do wacky things to your blood sugar

* Pettus J, Edelman S. Recommendations for Using Real-Time Continuous Glucose Monitoring (rtCGM) Data for Insulin Adjustments in Type I Diabetes. Journal of Diabetes Science and Tecnology. 2016.

2 Drawbacks to Continuous Glucose Monitoring

I have to mention that there are a few drawbacks to continuous glucose monitoring.

  1. Accuracy: First and foremost, it’s not always perfectly accurate at reading your blood glucose. In some cases you may be lower or higher than the monitor says. Just this evening my meter said I was 108 with a straight arrow. I felt awful, and so I checked with a finger prick and discovered that I was actually 55. It’s not a perfect system, and I find that sometimes it takes some time for my monitor to record changes in blood glucose. It is necessary to therefore always double check with a glucometer if your symptoms don’t match your CGM.
  2. Insertion: Some would disagree, but I find it extremely painful to insert. It can even be excruciating if I am unfortunate enough to hit a capillary. I have tried inserting it in multiple places and have found that some locations (the arm and the upper thigh) are less painful than others. Dexcom is supposedly developing an automatic inserter, so this may change.

Is it worth it?

You may be asking whether this is worth it. Is it worth wearing another annoying device with a separate receiver that needs to be changed every week? Is it worth the money and the pain of insertion every week?

I would say yes. As a diabetic there are over thirty different factors that can affect blood glucose at any moment in time. Testing blood glucose five to six times a day simply cannot give as accurate a picture of blood glucose trends throughout the day as thousands of blood sugars measured continuously. Continuous glucose monitoring allows for much greater control as it allows access to much more information. Access to this information allows you and your doctor to recognize certain trends such as: nighttime lows or morning highs (dawn phenomenon).

I personally cannot imagine going back to a life without my CGM. I don’t know how I would control my diabetes with just finger pricks alone. I remember when I used to have to carry a meter and test my blood sugar on a run, but now my pump alerts me even when my blood sugar begins to drop, so I can sometimes prevent those terrible workout-ending hypos.

To all you lovely woman out there afraid of the scarring, the pain, and the cyborg look: Get over it and go chat with your endocrinologist! The benefits in this case vastly outweigh the drawbacks.

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