CGM Medtronic Practical Tools

Now that I’ve used this thing for a few months (Medtronic 502 w/ CGMS Sensor) I have a few observations, not all of them positive, and would like to find if others are getting the same results.
First, I had to fight Blue Cross for the system, they declined repeatedly. When I made the final appeals out of their system, the state of California overruled their declination. I’m happy it worked out, but it became essential when I no longer could feel the lows.

Unfortunately the system is not really accurate, but provides only approximations under the best of circumstances. It is a tremendous improvement over the 15-20 times I was testing daily. My fingers have permanent pin holes everywhere. I know, we all do.
Most of the solvable accuracy problems in my experience seem to be caused by 2 factors:

  1. The sensor readings lag behind the meter readings by as much as 3/4 hour. This is acceptable, but means the warnings for your lows come to late. The solution, for me, is to set the warning higher (around 80) and keep track on an ongoing basis of whether you are going up or down.
    2.The warning beeping alone isn’t enough because the CGMS is simply not accurate.
    Accuracy is a big problem all the time. But if your initial calibration is off, you can’t fix it buy adding input. Start over.
    Your initial input can be off because you screw up and put in the wrong number, but more often you are trying to calibrate when your sugar is low, high, or in the process or rapid change. Any of these conditions will really screw up the first calibration. Unfortunately adding more meter data does not seem to help. I don’t know for sure, but it appears adding more data just causes the meter to average what has been input. Each addition brings it closer, but if you start way off, it does not fix the problem.
    You can fix it most effectively by getting your sugar under control, then telling the meter you have a new sensor. As others have noted, you don’t have to wait 2 hours when you trick your meter into stating over. When you start over the calibration begins with a clean slate.
    If you begin the calibration with blood sugars between 100 and 180, the meter operates with results amazingly close to those of your meter, but are still time delayed. Often this gap is as low as 10-12 minutes.
    If you calibrate when your blood sugar is below 80, or above 250, the system will read wildly inaccurately until you clear and start over. Also, if you calibrate, for example, when your sugar is at 80, and then immediately eat and take insulin, you greatly confuse the sensor. Sometimes it figures it out, but often you make a mess. It really does work best to start over, and stop trying to fix it. Often the 3 days is gone while you fight with the meter. Then you find bliss when you start the new sensor period. Don’t endure the agony. It does not seem to save on sensor life. And you are not a failure because you give up and start over. You own the darn meter, it doesn’t own you. REALLY.
    Keep in mind that the meter testing is required every 12 hours (I know, we all thought the finger sticks were a thing of the past), and extreme sugar levels, low or high, will also screw up your future accuracy. Fortunately update high or lows do not seem to throw the sensor off by as great an amount. If you input a 350 though (because you forgot a bolus or ate pizza and guessed wrong, either skip the 12 hour data (understanding this will cause trouble) or just start over as a new sensor when things get straightened out. Once you input a 350 or higher, you can forget the readings ever returning to anything close to accurate.
    So this is my input. It may be wildly inaccurate for you, but it’s what I’ve encountered in trying to figure out how to make this thing work.
    So do I like it? Absolutely. Even though it can be wildly inaccurate , when calibrated properly, it works reasonably well. While I can’t rely on it to accurately warn me of lows until its often to late, if the calibration is set right and the alarm goes off at 80, I know to check. If I see it is trending down and I get the 80 alarm, I check with the meter. Often I’m at 50 or 60, and still coherent enough to do something about it before I become the belligerent ■■■■■■■ who refuses help. And if the warning is wrong (or is right and it is just below 80), that’s great. I don’t mind finding I don’t have a problem if the darn thing keeps me from embarrassing and dangerous lows. And my friends and kids greatly appreciate not having to deal with me “in trouble” as often.
    Other comments.
  2. I love the Nexcare waterproof abrasion cover sold at Walmart. They are relatively inexpensive and much more flexible, removable and durable than the things Minimed sells (IV3000 by smith and nephew). It takes a little practice not to destroy them taking them out of the package, but it actually works just like the directions say if you take the time to read them. If not, you’ll figure it out after you wad up the first two taking them out of the package. You can guess how I did it.
    By the way, I don’t like the ones Nexcare sells with the bandage pad in the middle. You may prefer them if you don’t like having to peel the sucker off your sensor, but I find the ones without the bandage area stick better and last longer.
  3. I don’t know how the other posters here get 21 days out of sensors. I’m lucky to get 6-7 days before I get the “Lost Sensor” message, and no amount of new sensor starts or “Find Lost Sensor” attempts work anymore. Is there a secret I haven’t found yet? Please tell me.
  4. I hate the sensor warning beep. It is a generic electronic sound used for everything from warning of cell phone batteries dying to trucks backing up. It is in the sound range where anyone with mild hearing problems can’t hear it. You will discover people telling you you are beeping everywhere. And I find I don’t always feel the vibration since I’m a belt wearer. Has any one figured out a way to change the tone the way you can with cell phones. I’d love a distinctive tone. Something like a screamed “Your blood sugar is low and you are going to pass out” would be just fine. So if there is a techie out there who can advise, it would be greatly appreciated.

Thats it. I have no expertise. I’m an estate planning lawyer, for heaven sakes. And I’d love to hear whether others have similar experiences of suggestions.
Phil Christian

I have been using my CGMSfor about 2 months now. I am unlike most, and find unless I am going up or down very quickly,the sensor is quite accurate–within 4-8untis–sometimes right on—I get this much discrepency bewtween strips if I test twice (or three times if am not so sure of the reading).

If I run way up(200+)in can take a few hours for the sensor to settle back down…seems to recover faster after a low (<70)

I have been abek to tweak my basals and square wave to get a steadier (a bit higher) BG–pumping insulin said to kill the lows first and then work on titrating down the numbers.

Having had a very bad couple of weeks that included bad insdsul in and a leaky resevoir (wet inside the resevoir chamber–it made it through the 2nd O ring), I can handle a few weeks at being @ an average of 140 instaed of 120…the horrid lows are for the most part gone–a sneak one now and then…

I also am unfortuante in that I cannot go longer than 3 days with a sensor–not becaue I can’t get themto restart…I can…but my body does NOT like the sensor itself being in more than 3 days…period!

So change every three days I must…hopefully as they improve the sensors this will change.

I set my pump/cgms to vibrate—so it only alarms if I miss the vibrate…doesn’thappen very often

I have been fine with the IV3000–I thougth nexcare was made by the same people to make tagaderm–which does not like me much?

You don’t remove the sensor!!! You remove the transmitter. You also don’t tell it to find a lost sensor; you tell it that you’re starting a new sensor.

To get past day 7-8 you need to remove the transmitter and charge it. Once it has been charged tell the pump to find lost sensor. It will then continue to work very well, probably even better than when you first inserted it.
I would also agree that if you are looking for the CGM to be your new blood meter then you are going to be disappointed. The best results show up as trends on the Carelink website. I run my numbers within the green zone most of the time and when you look at my numbers over 3 months they are spot on with my A1c.

Thanks I corrected my mistake!!! It now reads transmitter. Dave

We have been using the MM CGM since November. We loved it then, now well… lets put it this way. This morning, my daughters blood sugars are stabalized all night long. I do a calibration at 5:20 this morning with a blood sugar 116. At 7:20, she is alarming and CGM says 52, ouch. Finger stick is 113.

I am so, so tired of the false readings.

Many times CGM is not budging over 235, and my daughters blood sugars are 310.

We are very careful when calibrating. I calibrate around 5 am. Then again around 4:15 pm. Then again around 11 pm when I go to bed. There is no active insulin. Blood sugars are with in normal range.

Did I mention I am tired of false readings. ARRRggggggg.

I find that the sensors do not do well with high BGs. I woke up this morning with a BG of 263 and the sensor was 104. The overnight graph was a totally straight line. Of course I got a calibration error when I entered the BG but the sensor had been in for awhile (I forget how long, maybe 11 days) and was ready to get pulled anyway.

The overnight flatlining really annoys me. I have a weird schedule and eat dinner after 9:00pm, sometimes closer to 10pm. Sometimes I want a snack before bed. Lately, no matter what I have I wake up high. I generally wake once or twice during the night (for no reason, except maybe my annoying cat) and always test if I wake up. I know I’m not going low & rebounding. My body has all of a sudden decided I can’t eat after dinner. Even a piece of light string cheese will send me high. The sensors never catch them. During the night is when I’d really like to be able to rely on it.

Dave … I know a regional director of the JDRF in Canada. She has told me that an implantable pump and CGM will be available in the next 2 years. I can’t wait to see that become available.

The CGM can’t be 100% accurate, it doesn’t measure the levels in your blood. I have been told you need to continue to use your meter and test your bg throughout the day. I went to a Pump Session at the Diabetes Clinic the other day and the Medtronic rep was basically telling everyone that they just had to use their meter twice a day to calibrate and that was that. I think it is terrible to give people false hope like that since this is really just the beginning of CGM and it is not something we can rely on 100%.

I had a great CGMS trainer from MiniMed who was actually ON the CGMS and pump. So that was a big plus. She helped us figure out all the little quirks to the CGMS that you only get if you are actually on it. :slight_smile:
One thing she told us is that the CGMS is most accurate when you are in range (100 to 200). After that, it can be off because when you blood sugars are high, or low, they often fall or rise at a VERY fast level and the CGMS can’t keep up since it is not reading your blood, but the fluids.
She recommended setting the CGMS low level at 80. And that works for me. Often times I am closer to 60 when the alarm goes off, but still okay enough to take care of my self.
Also, she told us not to calibrate if the levels are that far off. At least not right then. Example, your CGMS reads 210 and your “high” alarm goes off. You test in at 293. DO NOT calibrate. Treat your high and wait. Most of the time it is just catching itself up and needs a little time to regulate itself. Same thing with lows.
She also said not to calibrate when the arrows are showing on the pump. Because that denotes a rapid rise of fall of blood sugar, so your meter reading is probably not going to be the same as the CGMS and it would not do any good to calibrate. It would actually make your CGMS be wrong and may take a day to get it evened back out.
As for the lost sensor, that’s your battery running out. I usually can get to seven days before my battery dies and I have to recharge. That’s when I change to sensor, but if you want to keep it in, take the transmitter off and charge it and then do “start new sensor”.
Sadly, I have no answers for you for the alarm. What’s there is there. But I do like the fact that when I’m sleeping it beeps and if you don’t get it, it turns really shrill and loud and starts vibrating to. That’s what it takes to wake me up. :slight_smile:
I have had great luck with CGMS and wear one almost always. The most I take off is a day in between sensors and that is rare. I find it to be accurate about 75% of the time. The rest of the times are with lows or highs, which is to be expected.
My suggestion to those on CGMS that have had problems is to contact someone who has it and has had success with it and ask them what to do instead of just a regular trainer. They only know what the book tells them. Those of us who use it successfully know all the little tricks.

I’m on day 3 of being a new CBG sensor user. I appreciate your witty telling of the good, bad and the ugly of being “Sensored”. I am already discovering some of the frustrations you mentioned to be true to my newby experience. Bottom line so far is that I am enjoying having the sensor confirm what I have intuited all along. Fast falling BG feels rotten and now is easier to step in a bit earlier than I normally would to fix the problem.
Thanks for sharing.

I have been using the sensor and I find it very accurate. At times it reads the same value as the meter. Usually it shows a 20 % difference with the meter.

Hi, Phil. Lots of useful stuff which you posted.
I have used the Dexcom+ for over two years (not the same unit). My Endo. has told me more than once that neither the CGM nor the home glucose test is accurate. In fact, the dude refuses to even say which is closer.
This is my 60th year with T1 and, especially in my later years, have always tried to keep glucose numbers at a reasonable level. Because of this, hypoglycemia was all too frequent prior to my getting the CGM, particularily during sleep time. If it were not for my take charge wife of 44 years, I'd be long dead.
Since I began the CGM system I have not had one low sugar (of any concequence) event. To say my wife is pleased with the CGM is an enormous understatement.
When after seven days I see the hour glass symbol indicating sensor time is expiring, I immediately stop the sensor, wait two hours and then calibrate again. This gives me two more days at which time I change to a new sensor even though the hour glass has yet to reappear. This works for me and I figure I probably get a month worth of free sensors by the end of the year.
I set my alerts at 80mg/dl and 200mg/dl. My last A1Ch was 6.3.
Back in 1954, after being diagnosed, many of my parents generation felt I would not live to a ripe age. That was the prevailing feeling of those times. I quickly learned to dispise sympathy.
They, of coarse, were unaware of the great lady I would be fortunate enough to later marry.
Please keep in touch,