Insulin, Oh Insulin, Where For Art Thou, Insulin?

I can’t do it.

I simply just can’t do it.

I can’t bear to think that I’m throwing away as much insulin as I am with every cartridge change with Tandem’s insulin pump. It just doesn’t feel right. Not sure what I’m talking about? Let me give you a run-down.

With any competitor pump out there, you can fill the cartridge and probably waste an average of 10 to 15 units filling the tubing and site during set up. From there, you can simply run the pump down to no insulin at all if you’d like, and only be losing that 10-15 units. Over a month (if you change out every 3 days), you’re looking at a grand total of 100 to 150 units per month that you’re losing due to the space in the tubing that needs to be filled.

With *my* Tandem t:slim pump, because it’s made with a bag-design, the pump can’t read all of the units that are placed in the pump. (Emphasis on MY because apparently this is different for others. I must have gotten a dud or something) Take for instance, last night. I filled the cartridge with 160 units. The pump recognized only 115 units of that. That is a difference of 45 units that will not be usable unless after I use the cartridge, I draw it back out and re-use it in the next cartridge (which is TOTALLY not recommended). But if you were to follow everything by the letter, I am wasting a massive average if 45-55u per cartridge. That doesn’t even account for the extra 10 units that it takes to fill the tubing on top of the already standard 10-15 units. So, overall, 55-60 u per change out… every three days. That’s 550-600u per month. That’s a half of a bottle of insulin or more per month that I’m throwing in the trash can, never to be used. Just since starting back on it, in ONE week, I’m down a half-vial. I’ve NEVER used that much that fast on any other pump. I knew when I started on the t:slim that it seemed that I was using a lot more insulin, but I never sat down to actually do the math.

While I love the pump and how it works, and yes, I feel obligated to use it because it was just paid for last year, I also don’t think my insurance would appreciate the fact that I’m literally throwing out half of what they paid for. And at ~$206.99 for Novolog (I may or may not have called my local CVS to find out the cash-pay price….), I’m throwing out roughly $103.49 to $124.19 per VIAL. On the conservative side, that’s $100 per vial, and at two vials per month, that’s $200 per month… that’s a whopping $2400 per year! (verses the insulin waste of a traditional pump, that would be roughly 100-150 units per month, with more going to actually being used, that would make one vial (for me) last 24 days verses 14 days, so maybe 1.25 vials per month being used with about $26-$39 per month in insulin cost being wasted in the tubing… $312 to $468 per year. Head spinning yet? Mine is.)





Ain’t no body got time MONEY for that….

I don’t know about you, but if I were flipping the bill for someone to have life-saving medication and knowing that they were throwing out half of it because of how the delivery-device worked? I’d be pretty pissed off. That’s about $2,000 more per year in insulin cost to use this pump over another one. And yes, most people have insurance to cover this, but think about it! What if you didn’t??

As much as I love Tandem and their nice, lovely, reports, and the wonderful touch-screen, quick-to-use insulin pump, I can’t fathom that a pump that is supposed to be so “green” creates so much waste in an area that is so dear to us. Batteries are much cheaper than insulin, and can be recycled. Insulin can’t.

So, it is with heavy heart that I will not be using the t:slim pump again until they resolve this. I know they want to work with me to fix the other issues I had like the random highs and things, but until they fix how it reads the amount of insulin that’s in the pump, I can’t feel right in knowing I throw out that amount of insulin just for the luxury of using this pump.

(Just so we are clear – all of this is based off of experience I have had personally with the Tandem pump. As I have learned, every pump that comes from them can work differently (my first one calculated insulin even worse than this one). What I have said here is my experience and mine alone. If you have better luck with it, good for you. My thoughts here are also based on using the pump as instructed in the user manual as well as how I was taught. Any tips/tricks/reclaiming/ or reusing is not considered in what I have calculated.)



Filed under dblog, Diabetes

31 responses to “Insulin, Oh Insulin, Where For Art Thou, Insulin?

  1. I usually reclaim from my old cartridge to the new, it has’t been a problem for me to do that. I wait till the indication says less than 10U and can reclaim about 20U total.

    • Sarah

      I don’t reclaim the insulin to reuse it as I feel it’s been degraded sitting in the plastic. I know others that do, but I don’t feel safe doing it. Also, this post is written as if you were following instructions as written, with no tips, tricks, or anything of the sort. I don’t know how you end up reclaiming only 20 units, as with every cartridge I have ever changed out, I pull out what’s left out of curiosity and I have 40-50 units every time. It seems to be a trend that those of you who almost or completely fill the cartridge have better luck with the way it’s calculating the insulin in the cartridge, but I don’t need to fill it for a 3 day use, so I only put in 150-160, which may be where the problem is coming in at.

      • I think part of my results is when I wait till I have <10U left according to the screen. When I filled early a few weeks ago, it said I had 28U left, but I did get more like 40U out.

  2. Patty


    I don’t know how true this is, as the t:slim is the only pump in my house, but I would recommend an experiment.

    I know it’s not easy with Medtronic since the reservoir is filled so differently, but if there was a way to measure the units left in your insulin vial using the BD syringe provided by Tandem and put that same exact amount of insulin into your Medtronic pump – see if there is a difference in units available to use.

    I know my wording is confusing, but what I have been told is that Animas and Medtronic label their reservoirs with “usable units” and Tandem uses a BD syringe that measures in actual units and, as you know, the t:slim then reflects usable units when it is filled.

    Word is that they really aren’t that different and that all pumps have unusable insulin in them – it’s just that the t:slim’s is more evident because you see the change from syringe to pump.

    • Sarah

      Thank you for your comment. I will try the experiment, but I do know there’s not nearly the same amount left in my Medtronic pump cartridge as what I pull out of the t:slim cartridge when I’m done, just by looking at the volume of it.

      • Patty

        I’m not really talking about leftover insulin. I’m saying that the actual measurements are different. You think you are loading 200 units because that’s what the reservoir markings say, but if you drew that same volume of insulin up into a Tandem syringe, the syringe would say that you just loaded 220 units (or at least something different than 200).

        Maybe you could try it with water and see.

      • Sarah

        I actually just did this with insulin because I was setting up my Medtronic pump just to see. I videoed it (you can watch it here: ). I filled the syringe with 180u and then injected it into the MedT reservoir. It filled to the 180u line as well. So I don’t think the measurements are off, and if they are, it’s not that big of a difference.. and certainly not 20 units. But I appreciate the idea. It set part of my questioning to rest.

      • Patty

        Interesting. I’d always heard differently. Well, there goes that theory . . .

  3. What is confusing me, when I’m done with the cartridge I reclaim what’s left. It’s usually about 10 (give or take) units in the BD syringe (when the pump says that it is “0”). There is always insulin left in every system’s tubing, so that’s a null point. With 10 units left….how does that come to 45 units of un-usable insulin?

    With the design of the “bag” in the cartridge, it can not determine the exact amount that is present in the cartridge when first filled (something to do with the pressure). That is why it defaults to 240+ units (I always fill with 300 units). As it is used, the amount left in the cartridge adjusts to a more accurate reading. Otherwise, when you reclaimed the remaining insulin, you would get around 45 units. I almost always get about 10 units. That is typical of other insulin pumps.

    Not that I am trying to disagree with what you computed, but it’s mathematically incorrect. When I first got my t:slim I felt the same way. I am an accountant so I usually go right to the actual numbers and they will tell the picture. I recorded every bolus amount and accounted for the basal insulin during one entire cartridge use (all this information is in the history section on the pump). The total insulin used was 280 units. There was still insulin left in the tubing and I didn’t measure the unclaimed insulin left in the cartridge. So it actually does leave the same amount of insulin as other pumps do.

    The one thing that has changed for me is that I actually use less insulin with the way the pump delivers it. I have lowered my basal rates considerably (again, using less insulin). I have steadier bgs and my A1C has gone from 8.4 to 7.2!

    I just wanted to give you another perspective on the T:Slim. If you do the same “test” with your pump, I am sure you will find that it functions much the same as other pumps do when it comes to un-usable insulin (mostly the insulin left in the tubing, which has more to do with the length of the tubing).

    If you do the same and count how many units were used to bolus and what was used during basal delivery, you will find that it’s much closer to what you filled the cartridge with than you thought. I hope this helps!!

    • Sarah

      Thank you for your comment. I understand that my math may not match up to yours. Where I’m getting the 45-55 units is coming from the amount that I have personally pulled out of almost every cartridge I have ever used with this pump, and that’s running it down to 0 on the pump. (I only fill them with 150-160u at the time) The extra 10 I’m figuring is the extra it takes to fill the tubing because of the design of the pigtail. The same tubing can be filled using different pump with only 10-15 units, so why does it take 20-25 with my t:slim? doesn’t make sense. I don’t understand why it seems I’m the only one having this much insulin loss with this pump, because I’m doing everything as I’m told to do it.

      • I agree it seems like you are losing more insulin than some of the rest of us. This makes me sad. As a fellow t:slimmer I want you to love your t:slim and be as excited as I am about my own. What sets are you using and how long is the tubing? I use Insets with 23″ tubing and it only takes me a total of 16-18 units to fill the pigtail AND the tubing. If I (occasionally) use 43″ tubing it takes more like 22 units. I know you said to Jenny that many of us who fill the cartridge up seem to get better insulin use out of our cartridges and that may be true. I fill mine – and I don’t go by the ‘change in 3 days’ recommendation. I do for sets, but not for the cartridge. I don’t reclaim insulin from my cartridges, but I have occasionally drawn it out just to see what I get. It’s usually only about 10 units. Like I said, I’m sad you are having such bad luck with your pump and wonder why that is. Initially my reaction would be to say ‘bad cartridges’ but I’m sure that in all the time you’ve had the pump you’ve used many different lot numbers of cartridges. The other thing I’d say is ‘bad pump’ but I know yours has already been replaced once. Now I’m at a loss. I hope Tandem can figure this out so that you, and others who might have this issue, can feel more confident in using their t:slims – and figure out why this ISN’T an issue for other people. It is strange!


    • Gidget

      I totally get it Sarah! All I can tell you is that with my Medtronic pump ALL insulin is used except for what is left in the tubing. I’m okay with the Medtronic pump saying it is empty if It is going to continue to let me use the insulin. With the t:slim I don’t have that option because if it says it is empty I can’t continue to deliver it!!! I refuse to go against what Tandem says and reclaim the insulin and add it to more insulin and then wonder if the high blood sugar that I have is a result of bad insulin! I have had 3 t:slims now and the pump has never calibrated right on any of them. I always have at least 50 units left in the cartridge when the pump says zero!! At the end of the day all I want to do is use the insulin and not throw it away!

  4. Gidget

    I wish my pump only had 20 units left in it when it says it is empty. My t:slim always has at least 50 units in the cartridge when the pump says it is empty! Always!! Every time I have talked to Tandem about the wasted insulin they have been adamant about not reclaiming the insulin. It is not recommended. The wasted insulin really bothers me too!!

  5. Sarah,

    If you would place a call to the other pump companies, you will find that the syringes used to fill their pumps are ” adjusted” to compensate for the approximately 20 unit difference in what you put into the pump. The t:slim syringe is medically accurate. For example, when you fill another pump’s syringe with what reads 200u, you’re actually loading 220u.

    Give them a call; they are required to tell you this. Essentially all pumps waste about the same amount of insulin.

    • Sarah

      I have to disagree with you based on the differences in actual insulin I see at the end of a different pump’s cartridge verses what I have pulled personally out of a t:slim cartridge. I know that’s what we’ve been told that it’s medically accurate, but I’ve seen the difference myself, and I stand by what I have said.

      • To be fair – as an ex-Medtronic user – I know you can pump another 20u through a Medtronic pump AFTER the pump says you have no units left. T:slim won’t let you do that – when you hit 0 all delivery stops and you must do a change out.


      • Gidget

        At least you can still deliver the insulin and it isn’t wasted.

    • Sarah

      If you would like to see it, I did a video tonight of filling the syringe that comes with the t:slim cartridges with 180u and then using that syringe to fill the MedT reservoir that I have. Once filled with what the syringe had, it also measured 180u, so I personally don’t believe there is a 20u difference between the two.

  6. Mary

    The only way I know of to not “waste” any insulin is to go back to the manual syringe method, remember that?
    And I suspect if ACA does not get repealed, we probably will be back on syringes because that will be all we can afford!

  7. Liz

    I am in complete agreement with you, Sarah. Awhile back, I kept track of how many units I put in, how many the pump then told me I had & how much I was able to pull out of the cartridge after the t:slim said zero. The amount the pump calculated was always off by between 20-30 units compared to what I put in, & I would draw roughly that amount out of the cartridge when changing it. It killed me to waste that much insulin, when there are so many people that are in need…

  8. Gary

    No you are not the only one. I get so stressed over money.

  9. Eva

    Hi Sarah,

    I have the same problem! I just found your blog and this entry because I googled for “tandem insulin loss”. I got my t:slim only on Jan. 3rd, and it is my first pump. Every time I fill the cartridge, there are 40 to 45 units lost. I need 21 units to fill the tubing and prime the cannula, so there are still 19 to 24 units lost that I can’t use. I only fill the cartridge with 120 units at the moment, so maybe this problem is indeed worse when you don’t fill the cartridge up? Can you enlighten me as to how to reclaim the unused insulin (even though I know you are not supposed to do it)?
    I only got aware of this problem today, and will call Tandem right away and see what they say.
    Thank you so much for blogging about this!

    • Sometimes, before going to work etc, I do a change out early. I put the filling syringe into the white membrane and draw out insulin. Nets me usually about 30U. Then I pull that out, draw air in and inject the air into the vial of insulin just until I get to the insulin in the syringe already, then drawing new insulin up for a proper fill. I do not inject the older insulin into the vial,

  10. Kurt

    I just got a Tslim and have a similar experience, it won’t recognize a load more than 240u and I use about 100-120 a day. When I load 300, it says 230-240, and when it gets to 0 and stops pumping, there are 50 units in the reservoir.

    I am OK with a loss to fill the line and a small loss in the pump. But when the pump says it is dry and I can pull 50 units out with a syringe, something must be wrong.

    I wouldn’t say the medtronic doesn’t waste some insulin. The reservoir necks at the top, you never get that neck out unless you pull some air trying to recaim. I bet it’s 20 units.

    It’s not a show stopper for me, but it is nuts, because Insulin is EXPENSIVE.

    I guarantee that without insurance I would reclaim and recycle all this stuff to the greatest extent possible.

  11. Debbie

    I”m having the same experience as the OP. I filled with 100 units, the pump rigistered 40u. so now after a day and a half, it’s telling me I have ‘low insulin’ because I have the low insulin alarm set at 20…where did the extra 60 units of insulin go??? it’s crazy!!

  12. Dustin

    So I have had this exact problem since day 1 of using this pump. I put 210 units in the reservoir and I load the cartridge and fill the tubing and I have 165 units left that the pump recognizes. Now here is the other odd thing. I fill the tubing that was 25.1 units with every other pump (Cleo 90 43″ tubing) and it takes 28-30 units to fill it with the T-slim.

    I did a cartridge change tonight doing the same thing I have always done and at the end it read 60 units. WHAT?!?!?!?! I go through the whole process again this time wasting the 10 units I must “fill the tubing” with before I can stop filling and it says 100 units? that is still 50 missing units.

    I have contacted Tandem many many many times and I’ve gotten several different stories. None of them add up (pun intended). I have been told to fill the cartridge slower, I have been told that the reservoir measures differently (it doesn’t because I, like you, tested that theory and it was exactly the same), and I have been told they “just don’t know” where that extra insulin is going.

    I also love my touch screen and rechargeable battery but between the “water resistance” that isn’t, and the wasted insulin and the 5 broken belt clips, I will not be using this pump anymore either.

    Hopefully in the future they will put some R&D into fixing the functionality first and then focusing on the extra conveniences.

  13. Amy D

    I know this is an older thread, but I have to chime in. I love my T:slim, got it in October 2014. However, what drives me absolutely crazy is the fact the cartridge bag MUST have at least 50 units to work. I understand that’s not a lot for a lot of people, but for me, that would get me by on at least 2 days no problem. I have been in situations 3 times now where I thought I had enough to fill a new cartridge and tubing and AFTER priming the tubing -so wasting at least 10-18 units, it tells me it must have 50 units when I may have 48 let’s say. That is incredibly frustrating and dangerous because it would work to get anyone at least by until they can get access to a new vial of insulin. It is a major issue to me, one which makes me THINK at least about switching pumps yet again at the end of the 4 years. Will not go to Minimed tho.

    • Sarah

      I’m in the same boat as you. I use roughly 25-30u per day. It bothers me that it wastes so much. 😦

      • Amy D

        Wasting is bad- yes. But in this instance I’m talking about the safety and practicality of not being able to even use the pump if only 20-49 units are counted for after priming.

  14. Pamela

    I’m deciding between staying with minimal and going with t-slim. I’ve been using it almost a week and have wasted a great deal of insulin. I had one usage issue where one day the pump was working fine delivering insulin and the next night it wasn’t. I ended up after several “false” deliveries of insulin going back to a syringes until I had time to call support. When I disconnected nothing was coming out. The connecting plastic at the end of the pump had plenty of insulin though. I might put off getting a new pump and cgm until more bugs are figured out.

  15. Jim C

    I have been using the T-slim for about 6 months, I’m an engineer and have had the same concern with my T-slim, I have experimented filling with slightly different volume 175 to 215 units, I need about 150 for a 3-day use. I have noticed with my pump it recognizes only two fill increments at this range, 120 and 180 units. Given those I have minimized waste to 35 units by only filling with what it takes for the pump to recognize 180 units in the reservoir, for my pump it takes 215 units. The most waste generated in this range was when I filled the reservoir with 200 and it only recognized 120 wasting 80 units. During my pump training I was told about the 35 units of wasted insulin, what she didn’t say was that’s the minimum amount wasted. The problem in my opinion is the pump doesn’t have the ability to accurately know the amount of insulin loaded into the reservoir like a typical plunger location driven pump. It seems to me the loaded insulin volume could be entered by the user through the touch screen during the cartridge load procedure although I’m sure there’s some sort of liability issue with that method being used. I am happy with my T-slim but also bothered by the wasted insulin.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s