Dexcom and Tandem Link

Stewart @Hertz4319 as we all know, there isn’t a single piece of technology or medicine - diabetes related or otherwise - that is suitable for every one. Perhaps, given your experience with Dexcom, you might be better off waiting for a future sensor availability; such as the Dexcom G7 [if Dexcom ever gets around to submitting it for approval] or the Abbott Libra 3.

Now for my curiosity. How do you go about calculating “extremely inaccurate”? I know individual comparisons between CGM and fingerstick can vary significantly depending on your activity during the previous few hours and your accuracy of pricking a finger and getting a “good” drop of blood, or heaven forbid, dare to use an alcohol wipe instead of washing as instructions provide. How does your lab-test HbA1c value compare with the 90 day GMI on your Clarity report? Depending on your red blood cell turnover rate, these values should be similar. Although my lab A1c is often between 0.2 and 0.5% lower than the GMI [my red blood cell count is consistently low] I consider the calculated GMI to be a fairly good key to the accuracy of the G6 sensor.

Based on my input and values, the device automatically calculates and proactively submits insulin w/o me lifting a finger. I then find my % of “time in range” to be almost 100% over the past 24 hours. This excites me because it truly behaves like a natural pancreas. I’m 54 years old. I remember what it was like before I was diagnosed at 12 yrs old :slight_smile:

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How much adjustments have you made? How many basal rates do you have? Also we were diagnosed about the same I was about 1 month shy of 12.

Hi Dennis,
The wild inaccuracies is when the CGM says 60 and I don’t feel 60 and the glucometer say 120. I still feel my sugars. I still wake up at night if my sugar drops. Sometimes before the CGM alarm. With regards to the GMI and A1C it is maybe .01 off. I have to be honest. I think my AIC is because of my lows. My time in range varies from 64% to 85%. That is the only reason for me to get the pump.

I just started with a new endocrinologist and he is great. His office staff is another matter. So I have an appointment towards the end of September with someone new. I will definitely discuss this with him.

I called tandem today and found out if I go through insurance which I will they has a 30 day return policy.

Remember, if CGM is not level, CGM & meter can be miles apart.

I could certainly be wrong but I feel like you’re trying to find reasons to get a pump while wisely evaluating possible issues with Dexcom. My bizarre rationale aside, when you first posted you described yourself as hesitant to switch to a pump - at least combined with BIQ/CIQ. I don’t want to push you over a cliff but off you’re on the fence keep in mind: even if Dexcom is accurate enough to suit you, there are many factors that go into making the loop successful. Yesterday I got an alert that I was 55⬇️ (fingerstick was 65) because I had neglected to turn on Exercise mode and my trip to the store did a number on my numbers; then there are times when I turn on exercise mode and forget to turn it off. And from.time to time basal rates may need to be adjusted because the body’s needs change.
Don’t get me wrong - I have no regrets about my pump, my Dexcom or CIQ - I’m grateful to have them and many people on the forum boast incredible time in range and greatly improved A1Cs. But I’m sure I don’t need to tell you there’s still work involved and if you don’t go into it with enthusiasm you may find it a hassle.
Since your concern is with the Dexcom there is another CGM you could try - the Freestyle Libre2. It does not have all the bells and whistles of Dexcom - it doesn’t connect to the pump and you have to swipe to see your readings - but the Freestyle2 has alerts that sound even without swiping. For some people body physiology seems to interfere with sensor accuracy; if Dexcom is problematic for you, it might be worth trying this one. Also Freestyle lasts 14 days, is less expensive than Dexcom, and is available with rx at many pharmacies. Just a thought.

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Hi J,

I am not sure what you mean by the CGM being level.

It means the number reported by the CGM is less than plus or minus 2.5 for the previous 30 minutes.

| Hertz4319 Stewart
August 27 |

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Hi J,

I am not sure what you mean by the CGM being level.

@wadawabbit , keep in mind 55 & 65 are considered accurate by Dexcom standards. Plus or minus 20md/dL when under 85 & 20% over 85


Thank you for your response. I have really enjoyed all the response and it has thought me alot. I had an endocrinologist that didn’t really push the pump. Her theory was you still need to take your glucometer and insulin, etc always with you in case the pump fails. I agreed with her.

What has me really thinking about the pump is being able to stay in range longer. That gives me a true reason to try it. I went to a new endocrinologist and he said with a pump I could be longer in range. That is worth it to me to go on the pump. So I had to stop with my new endocrinologist because of his office staff. I have a new appointment in the middle of September. I am planning on going on the pump.

I know it will take time to get used and will need more work . I am okay with that. I spoke to tandem and they have a 30 day return policy. I like there are safety mechanisms in the pump.

Thanks, I know. I just mentioned it to indicate I did a comparison.

Good to know. What matters is that you’re comfortable with your choice and trust your devices.

As long there is a safety net I am.

wake up with highs. This is probably with the base insulin

I take lantus before bed

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Hi Stewart,
Sorry if your questions have already been answered, but I thought I’d share my two cents, since I just began the Tandem pump in January (after 20 years with the Medtronic pump).
Many people with the Tandem and dexcom use the Control-IQ feature to let the pump decide what insulin to give, etc. I don’t. I have found the Dexcom G6 to be far more accurate than the G5 (and much better than Medtronic’s system, by the way), but it sometimes indicates a low when I am maybe 95 or so. So I don’t trust it completely. Perhaps you could do the same: use the pump and the Dexcom (it is nice to see everything on one screen–super helpful for me!), but not go on Control IQ.
By the way, I am almost 70, have had diabetes since age 13, and have been on an insulin pump for the past 21 years. My A1C is 5.4.
I strongly recommend a pump, because it gives you so much better control in the little things. It is so easy to give myself an extra bolus, etc. I wish I had made the decision to go to a pump years earlier than I did, but I simply didn’t trust it completely. Now I do.
So I would be enthusiastic about following your endo’s advice about the pump, but personally I do not use the automatic Control IQ system, since the Dexcom readings can be wrong.

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Thank you very very much. I really appreciate your advice. It makes perfect sense to me. You really addressed my main concern. I will give you this example to back up what you said. This morning my CGM went off. Telling me my sugar was 71. I didn’t feel 71 and I have gotten into the habit good or bad of testing on my glucometer. My glucometer was 98. So I didn’t need to treat.

I do have one question for you. If you don’t mind. Why do you think you get more control from a pump then just giving injections?Especially since you don’t use control IQ.

Thank you Stewart.

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@Hertz4319 , @toddbeall

Gentlemen, in the last two messages the separation of CGM to meter has reared its ugly head again. Keep in mind several points:
[1] the accuracy of CGM-meter is ±20% for values over 80mg/dL according to these two articles from Dexcom:
Dexcom CGM vs Meter accuracy.

Is CGM Accurate:

[2] the issue of compression lows can also confuse the issue. Additionally, if the safety of CIQ throttles back insulin to a full STOP, G6-CGM takes extra time to re-configure itself, the BG goes up above the starting level of the CGM reported when the compression low began. This adds confusion to the interpretation of data. In the Tandem world all of this is covered with proper training in reading and understanding the data from Tandem’s integrated display software t:Connect.
Here is what I have collected about compression lows including a professional journal article.
BACKGROUND : Compression lows are caused by the person’s body pressing against the mattress, pinning the CGM sensor/transmitter (CGM) between the person’s body and the mattress during sleep. First, the interstitial fluid (IF) is the fluid around body cells. Most of the time IF is in constant motion and exchanged with fluid in the blood vessels call plasma or serum. During this exchange, IF glucose is enriched and cellular waste products are removed from the IF all over the body.

THE PROBLEM : When a person is in sound sleep and is mashing the CGM into the mattress, the IF is also mashed. It is this mashing or compressing of the IF that causes the IF not to exchange as it normally does. Since the cells around the CGM sensor wire continue to consume (eat) the glucose available in the IF of the compressed area around the sensor wire the glucose in the area drops.

OBSERVATION : It is this low reading in the CGM data seen as a nearly level data graph and then a sudden drop in the CGM report of the glucose level that constitutes the COMPRESSION LOW. Because it is a low reported by the CGM brought about by the pressure on the CGM, the term COMPRESSION LOW has been offered in pumping circles. Because the Compression Low is a low glucose only in the area of the CGM, a finger stick performed in response to a LOW alarm will show NORMAL. The variation between the finger stick and the CGM data leads to frustration and bewilderment, believing technology is the source of the error.

The next observation is the blood sugar measured by the CGM will return to a value near where the CGM line was before the drop in CGM value. The near level line, the drop & alarm, the finger stick of different reading, and the return to the near pre-alarm value is the full picture of the COMPRESSION LOW.

To additionally confound the facts, if an insulin pump decreases or stops insulin delivery during the compression low, the CGM report after the LOW may be higher than the CGM reported before the LOW episode.Proceed accordingly.

Here is a link to Susceptibility of Interstitial Continuous Glucose Monitor Performance to Sleeping Position

Stewart, feel free to ask more.

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Hi J,

Thank you very much for all the information. The only thing is I don’t have compression lows. I have the sensor on my stomach and sleep on my back. I start off on my side. Currently I switched the sensor on my arm because of what I read here and over all the CGM is more in line with the glucometer. Of course it has only been in my arm two days. Thank you again for all the information. I love learning all about this.

@987jaj thank you so much for your research into and explanation of compression lows. Now and then I suggest someone consider those as a possible contributor to issues they are having, and I try to explain but don’t do nearly as good and thorough a job as you have here.
I was wondering if you might consider copying what you just wrote into a topic on Compression Low? It would be an easy way for people to find the info and research you just provided without searching through different threads, and starting it as a new topic would place the info right at the top.
Thanks either way, and again thank you for the helpful information.

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