BG spike after infusion set change

I have used Medtronics pumps for 20 years and have recently moved to Tandem TSlim. My TIR is usually in the upper 80’s.
I am finding more often that after an infusion set change my BG spikes to around 250. If I wait it out, giving multiple boluses and on a rare occasion give an injection, typically after 3 hours it will return to normal.
I have tried changing the infusion set to check for a kink in the cannula and there never is one?
Any thoughts?

I wear a Medtronic pump and what you describe happens to me routinely when I start a new infusion site. It’s frustrating and I have no idea why it happens. I’m in auto mode 98% of the time. It has nothing to do with carbs, because I haven’t eaten any and I’m not having anxiety. So……I hope someone will chime in with some ideas.

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Dee- Do you wait it out or change the infusion set? Do you ever have a delayed spike, 12 hours after insertion?


Hello @edmundo this happens to me quite often with a set change (I use Medtronic quicksets) my observation is as follows: a set change for me causes irritation at the local site. This irritation can result in histamine. When I have this irritation/local inflammation/histamine reaction I have a lapse in insulin absorption. Which presents as a rise in blood sugar (a spike).

I can usually reduce the inflammation with a hot shower. If I change a set and THEN take a hot shower, I do not have a spike.

I can also reduce inflammation by mild exercise such as a walk.

Try these things and see if it affects the spike and how long the spike lasts. I also do a set change bolus of 2 units, which I can set in Medtronic as a “cannula fill” so it doesn’t count as iob. Tandem might have a cannula fill setting.

I can also have a bad set where I cannot resolve the high blood sugar or I get an occlusion alarm and I just change the set.

Good luck.


@edmundo, Most of the time it happens within a couple of hours, but normally resolves, though likely due to me doing a correction bolus. I don”t think mine would go on for 12 hours, even if I let it resolve itself.

Joe has some good ideas. I might try the shower suggestion. Normally, if near site change time, I remove the old one before I take the shower….hmmm……I can’t say I’ve noticed a difference. I’ll pay closer attention.

@edmundo @HighHopes , I used to have elevated BGL after changing my Medtronic infusion set - I believe it was caused by my body rejecting the set and becoming inflamed. Like @joe, I added a little more insulin, I forget now how much, to the cannula fill operation.

This can also be done with the t-Slim. Tandem has three pre-set cannula amounts based on the most commonly used infusion sets; there is also a “custom” cannula option where a user can add another preset button. Good luck experimenting to find what works for you.

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I recalled seeing another post on this topic a little while ago. Here’s the link - I hope it’s helpful:

This morning I changed my infusion set and didn’t take any special measures….no shower….no massage….and BG stayed at 120. The rest of the day, it’s been between 98-116. So……lol. Idk.


Might you have recently had a large bolus delivered in the ‘old’ cannula ?
If so, do not immediately remove the old cannula when inserting a new one as sometimes the insulin can leak out through the ‘hole’.
My technique is; when I’m collecting the new supplies, to get out the solvent and leave it in my bathroom to remind me to remove the old cannula at a later time. It works for me.

Same here. It’s one of the things that doesn’t seem to go away.

I have the same problem when I change my Omnipod five pod. My endocrinologist has given me Afrezza, which is an inhaled insulin, which works very nicely if I’m rising after a pod change.

My son and I, both tslim users, have had this issue. I have added a step to the change that seems to help. When the fill cartridge starts, I tap the cartridge/ pump to move any air bubbles up and out. You can see small bubbles come out. I then flick at the tube connector, watching for those bubbles to push all the way thru and out. My theory is there are air bubbles working their way out at the start of a new site and this step has helped with our sugars.

Hope this helps.

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I too have this issue. Frustrating how random it is. I am on a Medtronic pump with the Quick Set cannulas.
Of the people that stated they get irritation, do you actually feel the irritation? I don’t feel any irritation. I thought it interesting about the person that stated a short walk helps. I do notice mine gets better once I do exercise. Treadmill for 30 minutes, spin class for 45 minutes. Biking over an hour. Once I have activity, it comes down. I haven’t ever changed the cannula. I just keep giving insulin.

No. There is no pain or anything. It’s just temporary poor insulin absorption but it goes away most times. I have found hot (or cold) shower or exercise makes it go away very fast for me. Good luck :shamrock:

I have used pumps from three different manufacturers and have always had a severe low about 2 hours after changing sets. On my first pump I would get swelling with the soft cannulas, so I had to resort to the steel needle-type cannula. The only time I do not get this is if I had left an infusion set on too long and it was obviously clogged, so my pump kept delivering more insulin to bring the high sugar down, and that insulin should not have been counted as it was no longer effective. I have always wondered if high sugars could come from getting air bubbles in the cartridge, the air rising to the top of the pump and being delivered first. I know high sugars are a common problem for others, even though I have never had that problem.

When I got my first pump (a Minimed 504!) I was taught that large bubbles - ones big enough that you could see a space in the tubing - were problematic. So we were taught to tap the filling syringe to gather all the bubbles together, then expel them through the needle - that a few tiny champagne bubbles might remain but they were no big deal. That may not actually be the case given what some here have described - in just recounting what I was taught.

Thank you for the explanation joe!

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Karen @T1Dx2, I find avoiding bubbles entirely is better for me.

  • My process is to be certain that the cartridge is completely void of all air by purging the cartridge by sticking in the fill needle in at least two locations and then getting all air out of the loading syringe - including the needle hub.
  • Also, and very important, is never ever shake a vial of insulin and only fill with insulin that has been at room temperature for at least a full day, never use refrigerated insulin.
  • Do not push air from the syringe through insulin, keep the insulin bubble free; do not invert the vial until you are ready to draw insulin - the directions that come with pump equipment.

This happens to me quite a bit. I am on a Tandem now but I have the same problem as when I was on a Medtronic so I know it’s not the pump. (Although I find it SO MUCH easier to get air bubbles out of Tandem cartridges than Medtronic cartridges.) I talked to my doctor and she suggested it was probably poor site absorption initially.

What I do is a kind of involved, but it has worked better than anything else I’ve tried. To make it work and not ruin a site, I rotate through 6 different body locations in the same sequence. I also move the cannula site a little in each location each time to as not to over tax a single place.

I change my connection site every day. This doesn’t mean I take a site out and put a new one in every day… I leave two sites in at all times. When I am adding a new site, I take the oldest working site out and leave the newest working site in. The sequence I use goes like this:

  1. Leave the newer of the two working sites in and remove the older of the two working sites. (As mentioned.)
  2. Insert a new site and connect to it.
  3. One of two thing happens.
  • The new site works. Keep using it for 24 hours. (Skip to step 5.)
  • After 2-3 hours the new site is not functioning well. Switch back to the working site and bolus to get back to a normal blood sugar.
    There are two possibilities for sites not functioning well.
    Possibility 1. The new site was holding its own. If so, leave it in place. By ‘holding its own’ I mean my blood sugar stayed fairly level, but wouldn’t go down even with a couple small boluses. [Small meaning less than 2.5 for me.] (Go to Step 4.)
    Possibility 2. The new site was not holding its own, blood sugar just keeps increasing. In this case, I try to remove the new by the time I reach 250. That’s just a bad site IMO. I find this doesn’t happen very often. (Return to step 2.)
  1. Wait a few hours (I find 3 works for me). Switch back to the new site and use it normally. I find the new site starts working fairly well about 80% of the time. The other 20% it just continues to hold its own. Then it either starts working or it doesn’t If it doesn’t, it comes out before I go to bed and I switch back to the working site. (Go back to step 2… but not until tomorrow morning.) [I normally change sites in the morning because I don’t want to fight with a dodgy new site at night. Night time pump alarms. You know I hate 'em.]
  2. After 24 hours, switch from the working new site to the old site for 24 hours. (After that, go back to step 1.)

Like I said, it’s a little complex, but it works really well for me. You should rotate through at least 6 body sites, though. Less than that and you’ll probably wear out some of your sites.

I use tandem as well and don’t have that issue unless it’s in a bad spot (ie scar tissue, etc) which would impact any manufacturer. Since you have used Medtronic so long, you are prone to have scar tissue regardless of rotation or not. Possibly it is from that although you’re stating every single infusion set change this happens? Are you sure that there is not a mistake occurring causing bubbles in your initial basal? Are you using cold insulin? Are you priming the cartridge?