CGM Continues to Elicit Strong Opinions

In our last 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. But her opinion 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.

Sheila Payne wrote:
I read your article about CGMs and felt that you left out three-quarters of the facts. You basically only gave the positives. You touched on the “fact” that CGM is expensive and requires a “commitment,” but that was far too light.

My son has tried two different CGMs, and the result was the same in both cases. The first one he tried was the Medtronic Real-Time System. I bought the new pump, and he tried it for eight weeks. I begged them to take it back. I will say that Medtronic tried to work out the bugs with him, but there were just too many issues. The second attempt was DexCom. The issues were the same.

The CGM companies want you to calibrate twice a day at least, but you can’t calibrate if you have just eaten, have dropped or risen more than 40 points in 20 minutes, have just exercised, or have active insulin on board. Type 1 people have very little time when one of these issues is not in play. Also, you don’t want to calibrate too close to the last calibration.

My son’s CGM would be off as many as 100 points at times. If you try to recalibrate when it is that far off, it shuts down and you have to begin the whole start-up process again. That can be quite involved-especially when it shuts off in the middle of the night. Unfortunately, my son’s CGM was least reliable at night. According to the Medtronic helpline person, that was because my son was sleeping on it. Well, most people don’t sleep standing up. After a few nights with the CGM, however, my son and I were doing a little sleeping standing up-because it kept us busy even during the night.

The CGM gave lots of false alarms. The monitor would lose contact with the pump. The sites did not usually last longer than two days before they would start having trouble. Once a site did last six days, but it was not problem-free. My son thought the sites were uncomfortable, and there was pain involved in the insertion. If the CGM had worked, the pain would have been worth it, but it didn’t work. The sites for the CGM do not heal as well as the sites for the insulin pump. It is hard to have enough sites for both the pump and the CGM when the healing process is longer for the CGM. My son was doing more finger sticks than ever, and his A1c went up.

I have been told that many people have had great success with CGMs-by magazine articles, doctors, and the companies that make them. But I have never met a real person who uses one and feels any differently than we do. At this point, my son will not even consider trying another one.

As Paul Harvey use to say-“That is the rest of the story.”  I feel that these are important facts, and they should have been included in your article.


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 what used to be called “brittle diabetes.” My blood sugars would fluctuate wildly, even when I was 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, as two of my friends have died in the past few years.

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.

Just as when a patient is diagnosed, when there are major changes in health or lifestyle, or when any new device or treatment is introduced, there is a “learning curve” to CGM.  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. There are even others who wear it just so that they can help us!  They understand ALL the problems and are both sympathetic and wise.  There is undoubtedly someone on call who has experienced the same problem you are having. If you ask around enough, you will get help.

3) Don’t accept scripted answers.  One day I called six times.  When I reached the fifth person and he asked me what insulin I was using (after he looked at the record at my insistence), I said, “The same insulin I was using when I called a half-hour ago. Obviously you are not an experienced user and are reading from a script. I’d like to speak to your supervisor.” 

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.  If I feel that a representative does not have the ability to help me, I tell the person so (nicely).  And if he or she won’t get me another person, I hang up and call back.

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 (for Minimed, it’s 72 hours; I think it’s seven days for Dexcom), insist on getting a replacement sensor. If a service person refuses to do this, ask for a supervisor and politely but firmly state your case.  You pay good money (or your insurance company does) for this device and its equipment, so be sure that you get what you paid for.  You will be sent a new sensor within a couple of days, as well as a canister and prepaid envelope in which to return the bad sensor. (Never throw away a sensor if you feel it did not work properly.)

Now, as to 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.  

When you go to your sensor status screen, you will see a reading that says ISIG: a number of at least 2.00.  Before entering any calibration, look at the ISIG.  If you do not follow the ISIG parameters, you will get a CAL ERROR message, so don’t enter a number until you check the ISIG.

To use the ISIG, first check your BG. Then divide that nu
ber by 10. The ISIG can be anywhere from ½ of that number to twice that number in order to calibrate. Ideally, your ISIG will be 10 when your BG is 100. However, with a BG of 100, the ISIG can vary from 5.0 to 20.00, and you can still calibrate.

You NEED to learn this computation to use a Minimed CGM. All the rest of the rules they give you are just guidelines. THIS is the real rule! I have consistently broken all the other rules Sheila mentioned and have even calibrated while a bolus was in progress, but only because I used the ISIG rule.

For those who are not math geniuses, here’s an example of how to do it: Check your BG (250). Divide that number by 10 (25).  The ISIG can be ½ of that number (12.50) through twice that number (50) in order to calibrate.

B) Start up rules: These rules are the ones that you should be following. You MUST wait at least one minute (I usually wait longer to be safe) between each step.  Here’s what I do:

Remove the transmitter and sensor. 

Turn off the sensor feature on the pump. (Press “Sensor,” “Settings,” “Edit Settings,” and “Off.”)

Clean the transmitter with alcohol to remove adhesive, sweat, dirt, etc. 

Insert the transmitter in the charger.  Make sure it starts blinking.

The rest of this process is best begun first thing in the morning after a drink of water.  You need water to make this work, and you need time to make it work.  If you start too late in the day, you may still be struggling at bed time.

Insert the NEW sensor with the inserter, at the correct angle and while standing.  Be sure it is held down well before you move one inch! I usually hold it down with easily removable paper tape until I attach the transmitter and put on the IV 3000.

Charge the transmitter UNTIL the charger light stops blinking: not just 10 minutes as they often say, but until the light stops-usually ½ hour, maybe longer.  

Remove the transmitter from the charger. Watch to be sure that the transmitter light blinks (six times on mine).

Wait one to two minutes after the transmitter stops blinking. Then, and only then, attach the transmitter to the sensor.  Be sure they attach firmly and click. Press on the sensor and the transmitter and be sure that the transmitter blinks again.

When you are sure that you are “well connected,” tape down the sensor and transmitter with IV-3000. I sometimes use two patches to be sure it’s down tight and won’t move when I exercise, sleep, etc. This is very important, I have found, especially if you don’t want it to stop reading and then have to re-start.

Wait another one to two minutes.  Then start the sensor.

Drink a LOT of water from the beginning (when you disconnect) through the first day of start up.  The more fluid you have in your body, the faster that the sensor will “wet” and start reading accurately.

Turn the sensor feature on your pump back to “ON” and try not to hold your breath.  At this point, it may take anywhere from one to six hours for it to really get started.  Your ISIG will fluctuate until the sensor is ready, and it may give you any number of alarms (sensor error, weak signal, bad sensor). Just turn the alarm off.  Even if you get a “bad sensor” alarm, just disarm it and restart.

Call Minimed for help if necessary, but don’t remove the sensor. Never remove a sensor (unless it’s supposed to be done) until a Minimed rep tells you to do so and tells you that they will replace it.

When you get the “Meter BG Now,” check the ISIG and do a finger stick. If they coincide (see item B above), then enter the BG. If not, turn off the alarm and wait until the two readings coincide according to the mathematical formula.  

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 type 1 diabetic? 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.  I don’t have any good answers for anyone with site problems.  Obviously, we need to find ways to use less conventional sites.  But as someone who cannot fasten her bra behind her back, I have a hard time using sites that I can’t see.  And many sites that other people use are unavailable to me because they bruise too easily or react allergically.

I have only one piece of advice on site issues: antibiotic ointment (Neosporin, bacitracin, or store brand).  As soon as I remove a sensor or infusion set, I apply the ointment to the site.  And after every shower, I apply the ointment to my entire site area and make sure to cover every “dot” of a past site in sight! 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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