CGM Continues to Elicit Strong Opinions


By: dhtest

In our June/July 2009 issue, we published a letter from reader Sheila Payne, who wrote that we had been far too positive about continuous glucose monitoring (CGM) in our June/July article Get the Facts on Continuous Glucose Monitoring. Her letter provoked a stack of letters from people who believe that the benefits of CGM substantially outweigh its negatives.  To let you in on the debate, we are reprinting Ms. Payne’s thought-provoking letter here, followed by two equally thoughtful responses from readers.

Note: These letters were written by Diabetes Health readers who are not medical professionals. This article neither advises a particular course of action nor endorses continuous glucose monitoring as the best solution for you. We deeply appreciate our readers’ personal contributions, but urge you to contact your CGM company with any questions or concerns about your own CGM.

Don Muchow wrote:

Sheila Payne’s letter about her son’s bad experiences with CGMs left me feeling that the balance of opinion about their effectiveness has once again been knocked out of whack.  True, the technology is in its early stages, and some people, like Ms. Payne, have had negative experiences.  But my own experience has been relatively positive, and I would encourage others who are using, or are contemplating using, CGMs to consider both their positives and their negatives equally.

I feel compelled to correct some errors in Ms. Payne’s letter.  First, it’s not true that you can’t calibrate after you have exercised or when you have active insulin on board.  Even if the manufacturer’s literature says that- which I doubt-my experience has been that the devices will calibrate as long as the “sugar curve” is flat.  As far as “not calibrating too close to the last calibration,” yes, the manufacturer says that it’s possible to over-calibrate the device.  But in practice, it’s almost impossible to do.

I use a Medtronic, the same CGM that Ms. Payne tested.  The device has never shut down in the middle of the night unless it was out of enzyme or low on power.  And it has been as reliable at night as during the day.  In fact, mine has warned me about lows that I would otherwise have slept through!

As far as the device shutting down-yes, it is possible to get a “weak signal” if you are overweight and the sensor and transmitter are on opposite sides of your body, if you are in a building with wireless security devices, if you are in the shower and the device is on the counter, if the device has become partially dislodged, etc.  But the system won’t shut down unless the sensor has been off or out of range for quite a long time. In practice, this has happened to me exactly once in the last year-and-a-half.  If my computer crashed only that often, I’d be pretty darn happy.

The manufacturer makes no guarantee that the sensors will work past three days, and they tell you that CGM is not a substitute for metering.  That’s true.  My personal experience has been, however, that the sensors are good for about five days, which isn’t bad.  After that, several things can go wrong. The device can get stuck on one reading despite glucose actually going up, and readings can vary wildly up and down or be artificially high or low.  But that’s why they say to change the sensor, and that’s why we have glucose meters!

The point of calibrating, in fact, is to remove transient inaccuracies/false readings via a weighted regression of data.  The vendors tell you not to calibrate when your sugar is rapidly changing because there is too much change in the slope of the curve, and a linear regression on such a curve is inherently inaccurate.  You can, however, calibrate if your sugar “curve” is flat and high or flat and low. Given that you have to calibrate only twice a day, it’s not that inconvenient to find a time when your sugar is flat. In fact, the CGM system has helped flatten my sugar curve because I now tend to do “micro-bolus” corrections more often.

As far as irritation at the site and the size of the sensor, I agree.  The introducer needle is large and somewhat painful.  But I’ve seen worse. Things I don’t like: the fact that sometimes the sensor doesn’t go in all the way and I have to push the needle; the fact that you can puncture a blood vessel; the fact that insurance is just starting to cover the devices; and the fact that the dressings don’t really stick after a 10K run.  But you know… that’s life.

I truly, truly sympathize with Ms. Payne’s frustration.  It took me quite a while to get used to my CGM system.  But she seems to imply that only manufacturers or magazines paid by them have anything positive to say about CGM. As the saying goes, one exception breaks the rule. I’ve used the Medtronic system for a year-and-a-half with no major issues, and I suspect that there are many more exceptions like me.


Hillary Liber wrote:

I agree that there is a lot more to CGM use and management than one article can reveal, and I empathize with the problems that Sheila and her son had while learning to use a CGM.  However, I would like to share with you a bit more of “the rest of the story.”

I have had a Minimed CGM for over one year, and I have done three trials with various Dexcom devices.  There is no question that these devices are far from perfect and that the technology has a long way to go before it becomes more user-friendly.  Even in its current incarnation, however, a CGM is still a very useful device.  It just takes a LOT of hard work and time, and there is a LONG learning curve.

What I Get from CGM

Almost from the moment of my diagnosis, I have had “brittle diabetes.” My blood sugars fluctuate wildly, even when I am a “perfectly compliant” patient-eating and exercising in a consistent fashion from day to day, taking ten finger sticks and almost as many injections daily, etc. Even after completely mastering the Minimed Paradigm pump, utilizing its special features, and going through the two-week adjusting process every six months, I was still roaming wildly between 30 and 450.  

Out of curiosity (and desperation), I got involved with several studies of the Dexcom CGM. I could see the value of the device, but could also see that it was a LOT of work.  I decided to begin the (one-year-long) fight with insurance to procure a CGM, and I ended up with the Minimed Paradigm CGM device in June 2008.

At that time, I had a very reasonable A1c of 6.3%.  That was a false comfort, however, because I was having serious (below 45) lows almost daily. These extreme lows compensated for my extreme highs, so that my average looked artificially good.  Furthermore, I was having to test up to 15 times each day. I was afraid to do anything (drive, exercise, walk a few blocks from home, or travel by myself) without being certain that I was high enough (which generally meant too high!). More often than anyone would like, I was becoming so low that I could not treat myself.  Although I was always fortunate enough to have someone with me at those times, I was terrified that one day I would be alone and would die from hypoglycemia.

After working on getting rid of the lows for the first six months of CGM, my A1c jumped to 7.2%. But now I felt safe, and I even traveled cross-country on my own!  Since then, I’ve been working on getting rid of the highs, and my recent A1c was 6.5%. I feel very much “on the road” to stability.  This is the WORTH of CGM to me.

What It Took For Me To Learn CGM

I knew from my trial experiences that CGM is not easy to use and that it would not be a panacea for all my diabetes problems.  All I wanted was to feel safe when on my own.  But even that was a difficult goal to achieve.

I must admit that the learning curve for CGM is very long.  But there ARE ways to utilize the “system” to make it easier. I would like to share my insights and experiences with those struggling to make CGM work.

  1. Use the 24-hour helpline. I never used Dexcom’s helpline, but Minimed’s service is spectacular.  Don’t hesitate to call with even the silliest question-and definitely call when there is a serious question.
  2. Don’t accept the first technician you reach on the phone if that person is not helpful to you.  Ask to speak to a supervisor, or just hang up and call again.  There are many VERY competent representatives, many of whom have diabetes and wear the CGM for their own health management. 
  3. Don’t accept scripted answers.  Ask to speak to a supervisor if necessary.
  4. Trust your instincts. If it doesn’t sound right to you, there’s a good chance it’s not.  At this point, one year out, I know a lot more about CGM than many of the people whom I call for help.   
  5. DEMAND to receive what you are entitled to, including a replacement sensor.  If a sensor does not read within the first 24 hours, has not given accurate readings, or has failed before the guaranteed time of use, insist on getting a replacement sensor.

Addressing Sheila’s son’s specific problems

A) Calibration times:  If you follow all the rules that you get on the phone, you can NEVER calibrate-Sheila is right-on with that. (I was told even more rules than Sheila shared because I called so many times and got so many different people.) However, I finally connected with someone who treated me as the intelligent user that I am and explained how the calibration process works for Minimed specifically.

B) Start-up rules: There are specific start-up rules for every CGM. I recommend that you wait at least one minute (I usually wait longer to be safe) between each step.  (Enter 6334 in the Search box at to read the detailed version of Liber’s letter.)

C) Start-up times: I was told that it takes two hours from insertion of the sensor to first calibration. Yeah, right! Just as everyone’s diabetes is different, so is everyone’s response to any device.  I find that it takes a long time for my body to provide the amount of fluid to a sensor for proper calibration-sometimes six hours.  That’s why I ALWAYS start this process first thing in the morning. I don’t want to be up all night!

If it has been two hours since insertion and you have not had a BG that can be entered to match the ISIG, call Minimed and put them on alert.  Even though it might take four to six hours, you should get it into their records that there might be a problem later in the day. (Remember Rules 1 to 5 above. If someone doesn’t understand what you are talking about or makes you answer 20 questions before listening to you, ask to speak to someone else.  Your TIME is VALUABLE!)

D) Alarms: Because there is a lag time of 10 to 30 minutes (yeah, I know they say 15, but we know better!) between your finger stick and your CGM, set your alarms accordingly.

To start, most people set their high at 200 and their low at 80, but that might not be appropriate for you.  For me, having my low at 80 assures me that I won’t drop below 45 or 50 when the CGM begins to alarm.  As you get more experienced with the CGM, you can chose alarm points more appropriate for you personally. Then you will have fewer false alarms.

E) Night alarms:  I am a notoriously light and restless sleeper, but what I really care about at night is that I don’t get too low. Consequently, I leave that alarm functioning 24/7.

However, I do turn off my “high” alarm (or set it at a much higher number) when sleeping.  Also, I attach the pump to my nightclothes so that it always remains on the same side of my body as the sensor.

As Sheila’s son experienced, when your body gets between pump and sensor, it often gets a weak signal. I have found that it is OK to sleep on the sensor as long as you are also sleeping on the pump-so just keep them together!  Also, check the tape before you go to sleep. If it’s loose, put on another adhesive patch. They are expensive, but they make a world of difference. (If you have problems with the adhesive on the IV300, try another one. That’s the only one that I can use, so I mention it often!)

F) Weak signal: Whenever you disconnect your pump to shower, swim, etc., be sure you turn off the sensor feature. Then when you reconnect, turn on the sensor feature and click “Sensor,” “Start Sensor,” and “Reconnect Old Sensor.”  It may or may not ask for a new calibration, but at least you will avoid the entire start-up process.

G. Site problems:  Well, isn’t this the perennial problem of every person with type 1? I have very fragile, easily bruised, allergic, and derma-graphic skin. This means that I am a poster child for site problems. And besides the insulin site and the CGM site, I take three or four injections a day. Many sites that other people use are unavailable to me because they bruise too easily or react allergically. As soon as I remove a sensor or infusion set, I apply antibiotic ointment to the site.  And after every shower, I apply the ointment to my entire site area and make sure to cover every “dot” from past sites. Although it doesn’t get rid of the reaction problem, at least the sites heal more quickly for reuse.  One other thing that works for me is to dedicate a certain area for each “activity”: insertion, sensor, and injection.  That way, I know what is causing a problem and what is healing.

H. Finger sticks: Yes, there are days when I do more finger sticks with a CGM than without it. For me, however, it is worth it.  I haven’t passed out once since I got my CGM, and I’m even getting my highs under control. Two weeks ago I printed out my daily sensor overlay, and I had NO BGs below 55 and only one erratic high excursion. All my little graphs were in my target zone! Having a CGM is about better control. But good things come to those who WORK and wait for results patiently.  

I.  Changes in A1c: The last problem Sheila Payne raised was about A1c’s.  As I mentioned above, an A1c is an average. You may get a better average between your 40s and 400s than between your 70s and 200s, but you will be MUCH healthier in the long run if you control those highs and lows.Finally, I want to say this to Sheila Payne’s son, and to everyone struggling with managing diabetes. With or without a CGM, this is a CRUMMY disease! I want to strangle every person who responds to learning that I’m diabetic with a comment like “At least it’s not cancer” or whatever other disease they dread. People who do not have diabetes do not have a clue about how difficult it is to live with this disease.  

I’m sure that there are some people who find it easy to manage their diabetes. However, I have learned from talking to people at conferences, seminars, and doctors’ offices that most of us struggle all the time, or at least most of the time.  We’d love to believe that all the work we do and all the suffering we have will make us “all better” one day. But as of this writing, there is no cure for diabetes.  We will have it for the rest of our lives.  So don’t tell us it’s no big deal. It’s a great big deal. 

Therefore, Sheila and son-bravo to you both.  Bravo to you for trying. Bravo to you for your successes. And bravo to you for enduring your failures. I pray that you have greater ease in the future and that one day we can all celebrate the end of this disease together, for ourselves, our kids, and future generations!



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