Accuracy in pump dosing

I’m just wondering about the accuracy of insulin dosing with the different pumps. I’ve noticed there are days when my blood sugars seem way off since I’ve been on a pump. I’m able to get a new one now, and wonder if there is any difference in accuracy. Has anyone looked into this?


I had 3 Minimed’s then switched to Tandem’s T-Slim. At the time all the available pumps seemed to run neck and neck as far as bells and whistles, so with all things being equal I switched because I preferred the sleek look of the T-Slim and the fact that it could be plugged in to charge. Newer pumps now have some noticeable differences but accuracy should not be one of them given the nature of the device.
I didn’t notice any difference when I made the switch. I have found that I need to tweak my basal rates and/or carb ratios now and then, whatever pump I’m on. My basals definitely change winter and summer, and I need the occasional small tweak in between as well (non-diabetic bodies do this on their own so it’s no surprise that we have to as well).
Some people find a particular type of infusion set works better than others, and maybe that changes over time - there are silhouettes that go in at an angle vs. 90° (okay, 90° is an angle but you get my drift :wink:); some sets use soft cannulas while others are stainless steel… It would be nice if we could get a sample pack to see if one works better than the other.
Not to get personal but I find it harder to keep good control when I put on weight. It’s difficult for insulin to distribute through fat, and fat increases insulin resistance. A medical person (or someone who did better in biology than I did) can explain it better, but the best way I can describe it is to say that fat is a very irregular substance. If you’ve ever watched a medical show where they remove fatty tissue you’ve seen it’s thick in some areas and “airy” in others. It’s hard for the insulin to get through those airy areas to find tissue to circulate through, so it can’t get through the system to do its job. I’ve found that losing weight and toning up gives my insulin a more regular, efficient surface to travel through. That’s a very juvenile explanation but I hope you get the idea.
If your highs are occurring on a regular schedule every so many days you may need to change your insertion site more frequently. My CGM software shows me patterns by times of day but I didn’t noticed or think to connect highs to frequency of site change. My new endo instructed me to change my site every 3 days rather than every 7 as I had been doing, and that has helped some. Some people have found things improved even if they went from every 4 days to every 3 (what a difference a day makes).
Best wishes to you in figuring it your mystery - hope this gives you some ideas.

Time out! I feel a need to clean up a bit of confusion here (see below).

Let’s begin with the basics. There are no air spaces between the many cells in the body - except for the interior of the lungs, all of the tissues in the body are filled with either tissue cells, interstitial fluid, cerebrospinal fluid, or any of several other fluids.

When we take an insulin injection/insert an infusion set, we want the end of the needle/cannula to find the subcutaneous layer of the skin. The subcutaneous layer is “bathed” in interstitial fluid; delivery of insulin through the end of the needle/cannula into this layer ensures that the insulin will perfuse into the tissue/interstitial fluid and, then, throughout the body. If you inject insulin into a fatty tissue layer you will see no difference in insulin absorbtion. What does make a difference is if the tip of the needle/cannula comes to rest in an area of scar tissue or connective tissue - it is difficult for insulin to perfuse these tissues and, then, be absorbed from/through them.

Increases in weight can increase insulin requirements for a very, very simple reason. Our bodies use insulin according to a hierarchy that ensures fuel is and will be available “in times of ‘famine’ (so-to-speak)”. Since fatty tissue is our primary storage area for “potential energy,” our bodies “prioritize” insulin to, first, store energy in fat cells. Once fat cells are “satiated,” any remaining insulin will be used to “feed” other tissues.

Given the above “hierarchy” (i.e., feed fat cells first, then other cells get their turn) the more fat you carry on your body, the more insulin you will need to ensure “all” of your tissues are nourished. Losing weight (i.e., reducing the size, and, eventually, reducing the number of fat cells) will reduce the amount of insulin needed to nourish all of the cells in all body tissues.

Now, the above is a very simplified version of how things actually work. But, it is an adequate description to develop an understanding of the recommendation that persons who have diabetes will be well served to “shed” excess weight (i.e., fat). It doesn’t matter if the person has T1 or T2 diabetes.

I could go on about this for days, but I’ll stop here. The point is, a person who has T1 is well served to maintain a “near ideal” body weight. This makes it easier to manage insulin need over the long term.


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Thank you for clarifying things, Bill.

@pamcklein hi the simplest answer to your question is that ALL pumps on the market deliver insulin in tenths or hundreds of a unit and in my opinion ridiculously more accurate than you need.

Occlusion (partial) and the potential proximity to scar tissue or muscle tissue can mean differences in absorption which can give the impression that your pump may be doing more or less of a dose than programmed. Cheers!

Thank you all for your responses. I guess I wasn’t specific enough in my question or, maybe I was… I’m not concerned with the day-to-day fluctuations in my insulin needs. What’s going on is I’m ready for a pump upgrade and was wondering if anyone had found any difference in the reliability of their pumps before I switch brands.

Thanks for the info. i do appreciate it!

I personally have reviewed the technical specifications for Medtronic, Insulet and Tandem and find them all to be between 5x-10x more accurate in dosing than necessary… Put another way, they are all completely accurate, all reasonably reliable, and technically equivalent pumps… so pick the one you like! :slight_smile:

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Thank you all for your comments! @Joe: Your answer is what I was looking for.

I just wanted to let you all know I decided to go with the T:slim X2 since it is integrated with my Dexcom G6. I just did the training and started using it today. So far, so good. I like that I only have to carry the pump now and not have to worry about a CGM receiver as well. I’ll keep you all updated on how it is going!

Thanks again for all of your advice everyone!
Pam K.
T1D 54+ yrs and counting!