IIS/CGM insertion site scarring increased or decreased by duration of site use

I have T1D and just read the paper “Preserving skin integrity with chronic device use in diabetes” after searching for an answer to a question I have. First off its a great paper for anyone who hasn’t read it. Not enough is being done to look at how chronic device use can eventually force someone to stop using devices. I have noticed insulin pooling up in sites close to previous infusion/cgm scars and sometimes significant inaccuracies in CGM readings. A person only has so much surface area to scar up so theoretically each person has a max number of infusion/cgm sites even with perfect rotation. I alway assumed that every insertion causes scarring disregarding the duration of the infusion/cgm set use. I switched to u200 insulin to increase the therapeutic lifespan of cgm/iis therapy for me with significant success. But recently I have been told that extending site use can cause increased scarring per site. This has lead me to wonder whether the solution is more frequent or less frequent changing of the sites. Do you have any information on this question? I unfortunately just switched endocrinologists and my new one is convinced that u200 is causing both the pooling, scarring, and confusion the pump closed loop algorithm.

1 Like

I will read this paper later today, thank you.
For others here’s a link:

My personal experience is obvious irritation if I extend an infusion site past 3 days.


I don’t se why u200 would do worse than u100 if you just cut your rates in half on your pump. Do youse a lot of insulin? Because I figured out that each site can absorb no more than 150 units of humalog . I use somewhere in the 40s per day so normally I am under this , but sometimes I go over and sure enough my site will crap out. I have started using a small injection of lantus every morning in order to ensure I don’t over use my sites, I’ve tried a lot of different volumes, but 5 units seems to be the best, and it prevents DKA if I have my set come out or stop working just that little bit of insulin does make a difference. I was considering using u200 insulin if and when I switch o the mobi pump if it is ever released. It is supposed to hold 200 units, but my tslim that is supposed to hold 300 really only holds 250 at least that’s the most I’ve ever been able to put in it. I was hoping the lower volume would also make the sites last longer, but after reading your post, I’m not sure


I normally fit 300 in my tslim. I switched over to omnipod last week. I normally use about 80 units a day

How did u figure out the site can hold up 150 units. By trial and error?

I stopped using insulin pumps for this exact reason. Now I give ALL my skin over to cgm and just do injections. I found pumps for myself were gadgets for gadgets sake, rather than bettering my control or for easier living. With twice daily lantus, plus bolus doses all in 1 unit or under I can save my skin for cgm as it’s use has a far higher utility than my pumps, saving all my skin real estate just for cgm now

Yes i. Noticed on days when I gave more insulin, it crapped out sooner and when I started looking at the data, I was able to see I was changing my sites after about 150 units no matter how many days had passed. I altered my diet and also started augmenting with a very small lantus dose. Now I almost never go over 150 in 3 days. But I think it’s an individual think. I’ve heard people who pump 300 units in 3 days and don’t seem to have absorption issues ,but I also have allergy to the adhesive so it makes my sites more inflamed, so there might be more than one variable going on here.


I use about 21u/day and my sites begin to fail at 2.5 days - no matter which insulin I use. (Tho Lyumjev eventually needs a daily site change, so I just use small injections now when high). I’m going to focus more closely on sites that can go to 3 days to see if they are the ones that leave a 1/4tsp size lump under the skin.
Thanks for bringing this up.

Does iis = insulin infusion sites?

I’ve used insulin pumps for 35 years now and have concluded that insulin infusion sites are degraded by the amount of insulin infused and the time the set is left in service. The more insulin that’s infused, the greater the damage to the tissue. I think your idea to switch to U200 insulin is a good one. I would not, however, push the site duration beyond 72 hours. If you use a steel cannula, I would reduce the duration to 48 hours.

CGM sites, it’s been my experience, don’t cause much site irritation and heal rapidly.


When I was first DXD in the '60s I was taught to inject insulin in my thighs. After a year I began to have atrophy and sucken areas on both thighs, so I started injecting more in my arms and abdomen. It took 1.5 years to get those areas looking normal. But then again, back then needles were 23-27 guage. When I started MDI in 1980s I never had an issue.

My educated guess is that with pumps it is inflammation and infiltration of granulocytes forming a thickened dense area, and causing issues with pooling/loss of insulin sensitivity. None the less, it seems that it takes a couple of years for those areas to recover.

I do not think it is the insulin causing the issue, but rather the buffer that is used; e.g., Lumyjev is in a citrate buffer and will cause pain after a couple of hours (as someone mentioned above). And then the plastic used for the infusion site also will cause inflammation. So, it is a combination of the buffer and the canula.

The inflammatory response is what causes the damage. I change out sites every 2-3 days to avoid it, even if the site seems good. And even then, you can still have a bad site/blocked/bent infusion.


1 Like

What is u200 vs u100?

Normal insulin concentration is u100, or 100 units per mL.

If there are 200 units per mL, that’s u200 insulin.


Does it say 100 or 200 on the label? I never knew this.

It will show x00 units per milliliter or u x00. X = 1, 2, 3 or 4. U40 seems to be limited to veterinary us, but u80 is still available. It all relates to the concentration. Some people with very high insulin resistance will use u400. The syringes are different for each concentration if I remember correctly.

1 Like

It would say U-100 on vial.

U-200 would likely only be available in cartridge, and pre-filled. Cartridge must be used in correct pen that will dose correct amount based on units of insulin.

I have never used pens, and get vials of U100 novolog to load into my pump. I have U100 syringes for backup in case of pump failure.

1 Like

As far as I am aware, anything other than 100 is fairly uncommon. (for people anyway)