Dexcom and Tandem Link

A little about me I have been a type 1 diabetic for 48 years. My a1c is 6.3 and is around that for a long time.
I have recently changed endocrinologist’s and he thinks I should go on the pump. Specifically the Tandem with control IQ. I am a little hesitant.
I don’t have a great deal of confidence in the dexcom. I had a few sensor that were absolutely horrible. For the most part when I test the reading on the CGM against the glucometer they are most times more than 20% different. Sometimes they are spot on.

I know they should never be exact because the readings come from a different place. My concern is with the pump taking information from the dexcom what happens if the dexcom is seriously wrong.

The reason for the endocrinologist wanting me on the pump is to be in range more. I have low most days and wake up with highs.

Any and all comments or suggestions would be much appreciated.

Thank you

Hi, Stewart, and welcome to TypeOneNation!

I was wondering why your new endo wanted to change anything— a 48-yr history with T1D and an A1c that’s generally around 6.3% sounds a lot like it ain’t broke so don’t fix it — but if you’re both low and high pretty much daily, then I definitively get it. The emphasis these days is on “time in range” more than anything else for exactly that reason: to avoid damaging lows and highs as much as possible. Which raises the question: how low are your lows, and how high your highs? And if you’re willing to share, what is your current dosing regimen? If the lows and highs are consistent, it might be possible to tweak what you’re doing to correct them. Or it might not — there are limits to what injections can do versus a pump — which may very well be why your new endo is recommending a pump in the first place.

As for experience with the Dexcom, we’ve been using it for almost two years now (my daughter was diagnosed six years ago, and used finger sticks and injections for the first four), and it works great for us. You’re right about there being an error rate and a time lag, but the FDA is confident enough to permit dosing decisions off of the Dexcom alone, which goes a long way in my book. (For decades, every CGM on the market required a fingerstick before dosing insulin, and for us, that meant it just wasn’t worth the hassle.)

On pumps, we used Tandem for awhile, and Control IQ is brilliant, but unfortunately the Tandem infusion sites kept failing for us, so we went back to Omnipod, which my daughter loves. And someday, Omnipod will get approval for a hybrid closed-loop automated insulin delivery like Control IQ, and then we’ll be even happier. But lots of people love Tandem, too.

Are there specific questions you have or things you’re wondering about?


Thank you very much for responding. Over the years I have been somewhat resistant to go on the pump. I am probably one of the rare person that really doesn’t mind injections and since I had good control there was no reason to do it. I don’t use a pen I still use needles. Which from what I hear is extremely rare but I am used to what I am used to.

I take 57 units of tresiba at night and a shot before each meal. My carb ratio is 1:2 being 1unit insulin to 2 g carbs for breakfast and lunch. Dinner is 1:1.5.

I still have blood sugar awareness which helps a lot. My Lowes can go as low as 65. I tend to treat at 85 but the sugar does still drop until the treatment takes effect. The big problem right now is I am waking up with high sugars. I’m the 225 to 300 range.

The main reason the endocrinologist is recommending the pump is time in range. I have had other endocrinologist recommend the pump of the years and they could not give me a good enough reason to go on it.

I understand that the FDA says about the dexcom. I usually do let the number on the dexcom be what I use to make a decision but not always.

Here is my main concern if the dexcom is way off and it has been the pump will make a wrong decision which can cause problems.
I know very well what dka is and don’t want to do through that.

One last thing. My motto is I don’t let down diabetes stop me from living life. If I want to eat something I do and I take the appropriate insulin. If that shortens my life so be it. I want to enjoy life and not live in fear or worry.

Thanks again for responding. I hope this gives you some insight into me.

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Hi @Hertz4319 . Many Tandem users take advantage of on of the loops between their pump and Dexcom; basal IQ corrects to prevent lows, while Conttol IQ corrects to prevent both lows and highs. That’s assuming that the correct background settings are in place in the pump - in addition to Basal rates and carb ratios which may vary based on time of day, there are correction factors and weight. I know that must sound overwhelming. I’ve been pumping for about 25 years and just started on control iq last year. Prior to that I used Dexcom to keep an eye on my numbers - in my case they’re typically very close to a fingerstick - and made adjustments manually: if I was high I could do a manual bolus, and if I was low I could stop insulin delivery.
I think it’s good and important to know how to “go old school” so if you’re considering a pump I would recommend doing things manually for a while - at least a few months - before switching to BIQ or CIQ, and you could use fingersticks in lieu of Dexcom.
The key is having good basal and bolus settings in place whether or not you use a loop - it may take some time to find out just what settings work, and you may need more than one during the day - I myself have 5. Your doctor will start you off with a rate to start with a a baseline (they use a formula) and you’ll work with them to tweak things from there. Changes will be necessary from time to time, and as you become more experienced you’ll be able to tweak them on your own but do work closely with your doctor as you’re learning.
I’ve been pumping for a while and love it but not everyone does. Some people prefer injections, and say they do better on them. If you’re not sure you really want to use a pump, or feel very strongly about staying on shots, perhaps some changes in your insulin type/s and/or schedule would help with the highs and lows. Some people absolutely positively cannot get good control without a pump; others use them because of personal preference. If you have a choice and aren’t enthusiastic about pumping, try exhausting your current options with shots before you make a commitment to pumping.
Here’s a link to an upcoming presentation on upcoming technology. I don’t know how far down the pike they are - maybe they’ll announce that at the meeting.

Hi @Hertz4319 welcome to Type One Nation. I hear you. The only thing I can offer is that hypo unawareness gets worse with age. Your doctor is trying to give you the option to prevent a low you might not be aware of. I am a highly trained engineer with a specialty in controls. All CGM suffer both accuracy and timing which can show up as differences between a CGM reading and a finger stick reading. If you have to choose between the two, choose the finger stick.

The programming in pumps tend to be conservative. Which works in your favor. Also, tslim offers basal IQ which only limits insulin when you are low or trending low. This may be of use to you.

Congratulations on mastering MDI. No one is going to make you change. MDI works for plenty of people. The only real reason I pump is because long acting insulin doesn’t work well for me, and I like being able to change my mind and go from couch potato mode to active mode by turning off my basal. That’s it.

The G6 is the most accurate sensor I have used but the first 12 hours I simply ignore it, because it reads inaccurately low during the first bit.

Cheers. Welcome. And I hope you find this forum interesting and informative. :shamrock:


Hi @Hertz4319, I am almost as long term as you, and I understand your concerns. As you have experienced, you can have a great A1C and still have very fluctuating blood sugars. With a tool like Tandem+Dexcom, you can reduce those fluctuations. The benefit for many of us is better sleep, and just feeling better in general. I pumped for about 18 years, then went on DIY Loop for 1 1/2 years, and now I’ve been on Tandem/Dexcom for almost 1 1/2 years. My A1C on pump was around 7.2, on Loop around 6.4, and on Tandem 6.1. Yes, Dexcom varies, but if you test from time to time and when you feel “off,” it won’t be a problem. There’s a learning curve with AID systems like Loop and Tandem, but IMO it’s worth it. Also, a great benefit of T+D is you think about your diabetes a LOT less. It has made my life with T1D much easier. If T+D doesn’t create a financial hardship, I’d recommend trying it. I’d also recommend you check out a couple of the Tandemb/Dexcom/CIQ user groups on Facebook. Best wishes for the decision that’s right for you!

Thank you all for replying. This is exactly why I put this post out there. Like I said originally I don’t mind MDI. I am so use to it. The only reason I can see fore to change is more time on range. I am not a techie by any means but I can learn anything I put my mind to. I have been on the glucometer for almost forty years and thought that was a game changer. I have been on the G6 for about 2 years and over all I really liked it when it works.

I like reading in all the brochures if in doubt test on a glucometer. I think that say a lot.
I know no one can make me do anything. It is always my final decision.

Again thank you for all your input. I really do appreciate it.

@Hertz4319 Hi Stewart and welcome to the JDRF TypeOneNation Forum! Here you will find many thoughts and some excellent tips for managing diabetes offered by people who are experiencing diabetes the way you are; I don’t offer professional medical advice, only what I’ve encountered during the decades of my life with diabetes.

First off, a pump, any of the many types you could use, is not for everyone - some people have better diabetes management without using a pump, Personally, I used needle injections for 47 years before starting with my first of four infusion pumps. My primary reason for a pump was to cut-back from the 2,000 injections per year to the 330 infusion set implantations. Footnote here: Control IQ with the Dexcom G6 & Tandem t-Slim x2 is awesome for me with Time-In-Range [TUR] above 90% on the international 70 - 180 mg/dl scale.

Like you, my HbA1c was for years quite acceptable always in the range of 5.7 to 6.4, but as your doctor told you it does not reflect the more important TIR. Even though I was in the party that developed what has now become called HbA1c in 1974, I now can see its primary weakness. I thought everything was really going well for me with years of acceptable A1c averages until I analyzed my horrid Standard Deviation [SD] - calculated from my 8 daily finger-sticks. I imagine that is what you and your doctor are seeing and the recommendation for you to begin pump and CGM.

As for trust, my trust for the accuracy of my Dexcom G6 is higher than my trust for any BG Meter [BGM] - and laboratory and FDA agree with me. BGM can achieve a FDA 510(k) certification by the manufacturer presenting data showing the meter achieves the 15% / +/- 15 mg/dl accuracy range most of the time. The “iCGM” [note the lower case “i”] is the only device with FDA Approval for insulin dosing. The iCGM designation was created by The FDA to identify the Dexcom G6, the only device at that time to achieve the rating. I would only compare my CGM reading with a BGM reading when I know the “history” which includes glucose trending, last insulin dose, activity including food and stress factors. The 20% wiggle factor between finger-stick meter and G6 is the sum of differences from lab of 5% for the G6 plus the 15% for a BGM. An “FDA Approval” requires independent analysis under supervision of the FDA; there are at least two other companies with products under this analysis.

My suggestion? Give the Dexcom G6 another try. Use the Dexcom Clarity to collect and for you to observe where your BGL travels during the course of the day over a period of time. Seeing this information may help you [and doctor] assess if an insulin pump MAY be a wise choice.


Thank you very much. Just so you know I am not giving up on the dexcom at all. I really like dexcom and clarity is a great name for the software, since does give clarity to the readings. Like I stated my concern is what happens with the pump when the CGM is totally not accurate which has happened on occasion.

I am sorry if I gave the wrong impression. I truly believe the first greatest invention was the glucose meter. The second for me is the dexcom. Hopefully the third is the pump.

Again thank you for all the information. I appreciate it.

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My belief, and experience using the CIQ algorithm for 19 months, is that the algorithm has sufficient built in cross-checks and safety feature to prevent harm. You can do a search of reports sent to FDA.

The “most severe” malfunction I’ve experienced has been the result of compression lows during sleep - what I had to deal with was all insulin delivery suspended when CIQ detected sensor malfunction.

Keep in mind that correction bolus is only 60% of the amount calculated by subtracting Target from current BGL, dividing the result by YOUR ISF; this prevents over correction. There also is a minimum time period required between Automatic Bolus and no bolus can exceed the max size you program in your pump. You also must program a basal insulin maximum.

Included in the basic CGM set-up of the pump is your customary total insulin usage and your weight. These two factors place a limit on the amount of insulin that CIQ can influence during a 24 hour period. There are significant safety features built into, and tested, the Control IQ. Of course a User could bypass some of the safety features by entering incorrect Profile data - notably ISF - but why deliberately try to hurt oneself.

A second suggestion: don’t venture into CIQ if you are not comfortable with the tools.

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Thank you very much. Your post is very very informative and the information I need.

Hi Dennis,

I have seen a lot of your posts. I know you have been a diabetic for a very long time. Just wondering if you don’t mind do you have an complications? Thank you.

Complications caused by diabetes? Stewart @Hertz4319 , I think blaming diabetes is over-rated in the blame category used to find a scapegoat.

I’ve got a few issues that people attribute to diabetes, but looking at my family history diabetes might not be the factor - such as I’ve lived 20 years longer than my father lived. But all this should be discussed in under a different Topic - I don’t want to hi-jack your original subject line.

The one health issue I can directly attribute to many years of non-care or not caring about managing diabetes is retinopathy - in 1966 I was diagnosed with prolific retinopathy and told I’d be totally blind within two years. I found an ophthalmologist, Dr. Lloyd M. Aiello in Boston, who who had some way-out theory for treatment and wanted someone on whom he could experiment. Long story short, by the next year American Optical had modified a weapon-grade Ruby LASER which was used on me and a few other people - rest is history. That was the first of my many “donation of my body and mind” that lead to making life with diabetes much better than tolerable.

Hello Stewert. I have been a type 1 for over 42 years now. Every year or so my endo asks me if I want to switch to a pump. I always respond know. I use the Freestyle Libre 14 day and it works perfectly for me. The endo and I know what carb ratios to use for each meal, how much long term insulin to take at 11 pm. I have no issues. My last A1C was 6.3 and I have been as low as 5.8. If you exercise, take your insulin, and watch what you eat. You should be fine. You’ll hear it from both sides. Do what works best for you and your lifestyle.


Hi Geoffrey,

Thank you for replying. I understand exactly what you are saying. I up until now I have been agreeing with you. As you know A1C is only one indicator of how your control. Now with the CGM’S a new benchmark I’d time in range. That would be the ONLY reason for me to go on the pump. Like you over the years it has been suggested me but I could never get a good enough reason to go with the. Even though it would probably improve my time in range and I am still not sure what I am going to do and I am okay with that.

As far as eating right and exercising. Well those are two areas I need to do the most work. Again thank you for your reply. Have a great day.


Stewart. First welcome to T1N. I am on a CIQ with G6. I understand your hesitancy about a CGM.

I have been on a pump & Dexcom for 20+ years. My experience with G6 has been outstanding. Have labs averaging 6 times per year including an A1C & serum glucose. I am known to the lab phlebotomists in my health care circle. Physicians now expect any patient with a CGM and a glucose order to have the CGM value entered in the lab glucose notes.

My CGM to glucose comparisons has been consistent for at least 2 years. In that time the variance has been 13-18 mg/dL between the CGM and the serum glucose value. This is so stable and the G6 has worked so well for me, I haven’t needed make a finger stick in almost 2 years, since 10/2019.

I don’t want to advertise, but here is what the technology will do. The pix with the 92 is a 3 hour action between CGM (G6) and CIQ throttling insulin. The second is what a week of this has done for Time In Range or TIR. Note the averge BG, Standard deviation, & % of TIR.!

Screen Shot 2021-08-22 at 23.35.27|326x500

The red lines show where I was low & CIQ throttled back the insulin and even turned the pump off to prevent a crash. As the CGM reported elevating BG, CIQ turned it back on and throttled accordingly.

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Hi J
Thank you for your comments. I really do appreciate them. I agree with you. The GMI value is very close to the ,A1C I get from the lab. My initial concern was what the pump would do if the CGM have wrong information to the pump. I have be on the G6 now for about 2 years and it has happened not often but sometimes when the sensor on the G6 IS extremely inaccurate. To me that would cause the pump to act inaccurately as well.

The comments that have been shared here have been tremendous. The main thing I have gotten out of the comments is the pump has safety protocols on it to compensate.

Currently my situation has changed a bit. I just fired my brand new endocrinologist and I have an appointment in late September with a new one. So hopefully by then I will have spoken with tandem.

Again thank you for your response I do appreciate it.


Hello Stewart. Well, I have had Type! for 42 years myself. I had been using Medtronic pump 730g and tried their closed-loop system. Hated the CGM solution. Kept the pump, but started the Dexcon CGM. REALLY like it.
Recently, three weeks ago, I moved to the Tslim utilizing the Dexcon CGM. I have been amazed. Really. I am always a bit of a skeptic and work in the tech industry. I have to say this device with the Control IQ is great. I am truly pleased.

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I hope you don’t mind me asking why are you amazed?

Hi Stewart. I started on the Tandem and Dexcom last fall, after meeting with a new endocrinologist. I had been on a Medtronic pump for two decades, but I hated (and did not at all trust) the Medtronic CGM. It was constantly wrong, and there was no way I was going to update to a closed-loop system with that, so I completely understand your fears.

I have my issues with Tandem and Dexcom - I wanted them to be the magic sauce everyone that was on it claimed they were, but they are not magic. And after years of managing my own diabetes, I know my body better than the algorithm does.

That said, it is still miles better than before I had them. A few of the Dexcom sensors had trouble getting started and I had to use fingersticks to calibrate them, but once I have about three calibrations in, they were spot on. The first 6 hours or so on a new sensor I watch carefully, then I have 10 days of not worrying. It’s never caused me to go high or low with it’s adjustments.

That said, you can toggle the Control IQ on and off at will. My overnight numbers were completely irrational. For no reason, I would wake up super high, or super low. It wasn’t connected to eating or exercise or stress, and it wasn’t predictable so I had no ability to manage it. That was the main reason my Dr wanted me on the tslim, and it has totally worked. My night numbers are amazing. I wake up nearly every morning around 105, and the overnight line is usually flat (from about 2am on, I am hovering between 100 and 130).

I do sometimes turn off the Control IQ during the day, though. I can predict what my BG will be if I am in my routine, so it is a little like just taking shots. I bolus when I eat, and if my Dexcom warns me I am high or low, or I check and see it is trending one way or another, I can adjust before I feel it.

Also, it doesn’t make huge changes. Like, if you are really high, it isn’t going to bolus a ton of insulin all at once for you. It will give you a little and increase your basal and see where it goes before giving you more. The Dexcom allows you to see what is happening and choose to adjust yourself (or test, until you are comfortable trusting it).

It is expensive if your insurance doesn’t cover 100%, so take that into account. It doesn’t make the diabetes go away, and I still can’t get things perfect. It isn’t a pancreas. But it definitely helps, gives me more information, and seems pretty trustworthy.

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