Tandem: is there concensus on reusing or extending life of cartridges, sensors?

Tandem t:Slim x2.
Although the documentation for sets, cartridges, Dexcom G6 sensor have defined times frames to be changed at defined intervals, in pursuit of financial savings, are users religiously following those guidelines?
It was a shock to me that t:slim cart with Humulog insulin is 48hrs.
That is a very short timeframe to have to replace a cartridge!
(I realize there is an element of “legal declaration, protect the company” statement about the use of the product, even though the product will be effective longer that 48hrs); it’s a CYA statement.

Of course I am eager to get the lowest cost of use for the technology, without jeopardizing my numbers using product that should have been changed out 2, 4, 19 days ago!
I see lots of effort to extend the G6 Sensor beyond the 10days.

What are people finding in terms of reuse (cartridges), or extending use of G6 sensors beyond the recommended time frame and maintaining their best control? I’m 17units away before my 1st cartridge is depleted, and looking for some user experience.

I can only comment on cartridges, but for me I find the insulin is fine even after 4 -5 days without changing it out. But other people have reported less effectiveness in their insulin after 48 hours. This suggests that it varies from person to person.

I suggest just try it. Start with 3 days, then 4, then 5 … etc. If you don’t find your BG sky rocketting, then its a good sign that you should be ok - but repeat monitoring several times before you conclude this.

Also, I’m not sure which insulin you are using, but some insulin like apirdra doesn’t work well on the tslim. The insulin solidifies around the 48 hour mark hence will start causing occlusions. I have since switched to novorapid when I transitioned to the tslim pump.

I completely fill the cartridge with Insulin (Novalog) and use until depleted regardless of time. Insulin is a pretty durable drug.

No issues with my control.

Thankyou for those replies.
I’m running Humalog. I was dumbfounded, blindsided by my CDE who advised me of the tendancy of Humalog to become “denatured in plastic” after 72hrs, recommending change cartridge with the set: 3 day cycle. So only load a 3day supply of insulin in the tslim cartridge, seems like such a waste of space for the 3ml cart. I certainly was not doing that with Animas & the 2ml carts, & Humalog last month!


“Denatured in plastic” is a pretty broad claim. Aren’t insulin pens made of plastic? And can’t Humalog live in a pen until it’s expiration date?

Now I don’t know exactly which plastic is used for either the fluid contact portion of a pen or the “plastic bag” inside a t:slim cartridge, but something smells fishy to me about this claim.

I run t:slim infusion sets and cartridges routinely for four days with Humalog and have never seen a problem.

Stay safe!


That is a legitimate concern with Humalog for SOME people, but not most. You will often see battles rage about this because happy Humalog users don’t believe the one person who speaks out. I have no idea how the same insulin, in the same pump, can behave differently for people… But it does. The only thing I can say is try for yourself and find out.

I use Novalog, so can’t comment directly. I’m one of the people who sucks the extra insulin out of the cartridge to use in the next one, though. Theoretically, I’ve got a minute portion of insulin from my first ever cartridge still floating about. LOL I can’t say I’ve noticed any problem with denatured insulin or occlusions.

I actually do change my cartridge with each infusion set (unless I’m just replacing one that got ripped off). Mostly because I’m OCD and hate accumulating extra cartridges. They’re one of the things my insurance covers 100%, so it’s of no consequence. MANY people do reuse them, though. If you choose to do so, just be aware that you risk more occlusions and reduced insulin efficacy. You may also never see a single problem.

I have been filling my tandem cartridge with 200-250 units (Novolog). Lasts 4-5 days. I change it when down to <20. I change infusion set 3-4 days, which may or may not correspond with cartridge day.

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@MM1, Ty. What insulin type are you using, for those ~ 250u?
I had always filled my Animas 2ml cart, & never had occulsions.
However, the 6-7day time frame, may have been the cause of swings, I just never conected the dots.
I do know, if I had over bolused, even at day 7, on an almost empty cartridge, the insulin was still capable of driving me to into hypoglycemia.

The actual reservoir is glass. The Asante Snap pump, which I used for about 4 months before the company cratered, used Novolog pen reservoirs, which was actually a pretty cool idea—easy to just plug it into the pump, and there was no limit to reservoir duration due to “denaturing,” though you still had to switch sites every 3 days. That said, I’m not that confident about the denaturing thing in plastic reservoirs anyway. I’ve actually been going four days on a single plastic reservoir, sometimes a bit longer, because I’ve recently lost quite a bit of weight, so my daily usage is way down, but haven’t changed my habit as to how much I put in the reservoir. And I haven’t noticed any issues.

Your question about sensors. I use a G6 and every time I try to reuse a sensor I get an ERROR message. I often find the site has “dried” up. No more blood. I see on YouTube folks are extending the sensor life but I have not found that to be so. Good luck.

I am still too scared to extend my G6 because of the amount of sensor inaccuracy that I see and the fear that might get worse. Perhaps I am just being a chicken, but I feel like I see a high amount of sensor inaccuracy on G6. I’ve prob been on G6 long enough, that its time to try extending…just to see what happens.


I wonder if insulin “lifespan” in a pump has to do with occupation (do they work in a warmer environment) or just metabolism (I am ALWAYS hot). I do not use a pump…yet. It was just delivered to my home a week ago and I won’t be home until Christmas to get my training…so no actual experience to offer.

With newer tandem and medtronic pumps the insulin is adjusted as your bg changes (from cgms). So even if some degradation in insulin, the pump would adapt delivery.

Most of time my pump/insulin is “room” temperature. Occasionally at night I roll on top of pump and it feels much warmer, closer to body temp. But have not noticed any problems.

Your experience may vary, and following 3 day pump fill may work better for you.

Which pump are you getting?
Tandem has training videos online, which I watched for my training. But had also used pump for 25 years. So did not do in person training. Met with endo (online) to review startup settings, if needed changes from prior pump, and endo reviewed my first couple weeks using T:Connect data and sent me some suggestions.

I opted for a Tandem pump. I got the Dexcom CGM in April knowing a pump was in my future. My pump was delivered 2 weeks ago to my home in NY but I am in California on a job assignment. I won’t be home until Christmas Eve. So, pump 2021 it is!

My endo says I have to go to a 3 hour training but they won’t set it up for when I go home the end of December because I am in California and they feel that NY is going to add Cali to the list of states that must quarantine for 14 days upon arrival. That leaves me in limbo. This has been endo limbo 2020 for me.

Sorry to hear of limitations they are imposing. Is this is your first pump ?

I’d still recommend reviewing the online videos and asking questions here in the interim so you get up to speed quickly once you are back in NY.

Yes. This is my first pump. My new PMD placed me on Lantus last year because my A1C was over 11. I went to a new endo Feb this year and she changed everything. I am on three different injectable meds and lots of injections (6-8 daily).

Thanks, I do ask questions and use this site to try to find info.

I’m currently working on trying to get my Dexcom to work with an android phone that is not compatible. I am not tech savvy and am struggling with it. I just bought a new phone Saturday. Brought the list of compatible devices with me and the guy showed me what he had in stock that he said was on the list. I got back to my hotel room…not compatible.

@SusanS: agreed with @MM1, enjoy the suite of training videos on the Tandem site, as well as a host of Tandem YouTubers. Great information.
When you get home to NY, and if required start the 14days isolation, crack open the box, USB charge up your new pump, and start playing! It is just an electronic device, play around, get to know your new best friend. When you do get the mandatory training, if you’re currently on a pump, you could have your settings already ported over to your t:slim before class begins. You’ll be fine! :+1:-Peace.

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@Susan, your phone and Dexcom, you’re having exactly the challenge I asked about here, and got the solution here! What is the phone manufacturer ( Samsung, LG, iPhone ? ), and model ( Samsung S20, LG K8, …? ). The advice given in this thread (Looking for examples not-supported SmartPhones working with Dexcom G6 application), to get a software that will run on a non-support device, resolved the challenge for me.