No Correlation

I am a new CGMS (Medtronic) user. I have successfully set my sensor up. It transmitts data to my pump with no issues. I calibrate it well within the recommended timelines (6 hours after the first calibration and 12 hours thereafter). I get pretty decent correlation for the first half hour or so, but no real correlation after that. My readings are as close as 40 mg/dl and as far off as 150 mg/dl. Neither is useful, even for trend data. And the descrepancy goes either way. I’ve had CGMS readings saying I was 130 after a meal and a finger stick that was 245. Ouch! I wanted the CGMS to catch these undiscovered highs in the first place. I’ve also had CGMS readings at 110, felt low, tested and my finger stick was 55. No good!

I have gone so far as to ensure I have no active insulin or converting carbs for the full 2 hours that the new sensor is starting and certainly when I calibrate. My ISIG values are typicaly around 12 (give or take a few points). I don’t know enough about how these operate to know if this is a problem, but I’m wondering because the testor is expected to produce ISIG values between 24 and 29. Also, anyone know what’s going on in that 2 hour period when you start a new sensor?

It looks like others had similar issues from the ‘120 point difference…’ thread, but the issues ultimately cleared. What fixed it for you?

I would really like this to work. Any pointers?

Not sure what I’m doing differently, other than perhaps getting better at my calibration and/or my expectations are better, but this thing seems to be working pretty well now. I think part of my problem was that I had some unexplained lows that were wreaking havoc with the monitor as I struggled to maintain my sugars, although i still don’t know the root cause of the lows, I seem to be through that now. Also, and I see this mentoned in other locations, there’s a definate lag in results. for me, it seems to be about 20 minutes.

My early thoughts on this…

  1. It provides great trending information.
  2. It will tend to catch a wayward trend faster than I normally would because I generally test no sooner than every 2 hours. So, even if this lags my actual BGs by 20 minutes, this is still catching soaring and dropping BGs 140 minutes before I would (with the exception of lows that I catch symptomatically).
  3. It definately doesn’t replace finger sticks, but I expect as I get more comfortable with it, it will mitagate a few for me. It still takes 2-3 calibrations per day (which require finger sticks). I’d still do a finger stick before meals. And I’d stick with finger sticks when you expect the potential for quck changes (e.g. during strenuous exercise).
  4. If you’re fluxuating wildly, this device will have troubles. Because if the lag time, you’ll probably think it’s way off, but upon close analysis with your Endo, you might be able to use the data to stabilize things.

So, if you’re contemplating one of these, at this early stage for me, I’m quite pleased with the way mine is functioning, but you have to keep your expectations in check. It’s a great tool, but it’s not the answer to replacing finger sticks (at least not yet).

I have found that it is very important that the sensor has enough interstitual fluid flowing around it to get a good ISIG. This means there must be enough fatty tissue at the site you are using. There is a 5 minute “wetting” period before turning the sensor on but I find that several hours actually works much better (for me). After the first callibration the next is due within 6 hours and I find that within four hours works better. I get better, closer correlation if I callibrate 3-4 times daily instead of just 2.

So glad that the CGMS is working better for you now. I felt like there was more of a learning curve with the CGMS than there was with the pump. Its a great tool but certainly not foolproof yet.

Donna is on to something. when you are callibrating look at the graff If you have been farily stable for the last 20 to 50 min.s that is the best time to callibrate. Have experanced some of the problems you have and can trace it back to callibrating while BG is changing. Great trend spotter.

Is your ISIG better than it was? An ISIG of 12 is good if your blood sugar is 100, is low enough that I’d pull the sensor if my blood sugar was 200.

At a bg of 80-120, I want ISIG times fifteen to be greater than my BG.

I have the Medtronic CGMS too. It is a loaner given to me by my endo on Friday, Sept. 5. I have to return it on Friday, Sept. 12. I have used it for 6 days and more than 90% of the time the CGM numbers differ from my meter numbers by 20-100 points. I thing I should be getting better results after 6 days. I use a Free Style meter ansd I trust it without question. I doubt that I would ever trust the CGM I am using. I have a friend who uses the Free Style Navigator CGMS. He is having fantastic results. I wish I could use one like his. My endo does not support any pumps or CGM’s except Minimed. I guess I will turn in my CGM tomorrow and forget about using one in the future. I am discouraged. I had high hopes for good results.

I’ve been on my MM cgm for a month now and I LOVE IT!! Even though I’m experiencing most of the challenges mentioned elsewhere (wide ranges, the learning curve issues, lag time etc…) I’ve made sure I KEEP MY EXPECTATIONS IN CHECK. I watch the graph regularly to see what the arrows are doing. Am I rising slowly or quickly? Test and do a tiny coverage if needed…am I dropping the same? Test again and if needed do a temp basal rate or eat a snack…

I will keep up on using this fabulous little mate, knowing that the company will keep improving it. I can’t wait for my next A1C!! [Who just wrote that???!!!]