Frequent occlusions with Novolog in pump

I have occlusions while using Novolog in my Tandem t:slim with TruSteel infusion sets. When I use Humalog, there are no occlusions. I have searched for a reason for this so I would have an explanation or a solution but there is nothing that I can find with a search engine. My doctor is not helping, as if I’m the only person with this problem so it must be in my mind. I have talked to Tandem and they’ve never heard anyone complain about this… Does anyone have any advice? My insurance doesn’t cover Humalog so I can’t just change a prescription.

Both have always worked fine for me. The only thing I can suggest is that you tell your doctor you would like to try to get an override on your insurance. Companies may make exceptions for medical necessity, and although your doctor doesn’t “get it” the fact remains - it’s not working for you.
As one of my managers used to say, What gets measured, gets changed - so show your doctor the occlusion alarms you’ve gotten, resulting high readings, etc. - they will need that to make your case.
BTW, are you getting alerts, or are you assuming there an occlusion because your numbers are going up? Most people can use either Novolog or Humalog without detecting any difference, but some people cannot switch between the two. If that’s the case your insurance should cover the one that works for you once you document it.

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I’ve been getting the very loud alarms in the pump. It always happens around 12 AM - 3 AM instead of during daylight hours. Yesterday it started at about 5 AM and a few more times through the day where I would change the infusion set. I changed to Humalog at the last alarm and haven’t had another alarm since then.

Thank you for clarifying. Sometimes I like to suggest something “just in case.” Interesting that it happens during the same timeframe - I wonder if you might be lying in such a way that it bends the cannula? A longshot I know but I like to throw out crazy ideas.


I try to insert them in a spot that won’t be compressed during sleep. I check the trusteel every time I pull them out and the cannula is never bent.
I just got a callback from Tandem and they said the insulin in the vial may at fault and to try a fresh one the next time. I’ve never thought about that. I keep all the insulin in the fridge and didn’t think that could possibly be the problem. That will be in a couple of days so if it works I won’t have to go through the trouble of writing a letter for medical necessity and hope it gets approved. Do insurance companies deny those usually or give you what you request without difficulty?
Thanks for the idea and I’ll let you know if the fresh Novolog works out.

The times my doctor has had to request an override for medical necessity have been when insurance choose as their formulary an insulin that was not approved for pump use(!). So those overrides were pretty simple. I don’t know that they usually are but I hope so.
Have you ever tried the “soft cannula” sets?

I started using this pump with the AutoSoft XC and after a short time found I am allergic to the plastic cannula.
Sounds like an override won’t be a struggle. That’s a relief.

Terry @wadawabbit, I too immediately thought that the issue might be the result of your sleep position in that it appears to happen only when you are sleeping - @wadawabbit. Years ago, several members of the Medalist Group reported Humalog “crystallizing” in Minimed pumps, but not Novolog.

I was told way back when to never fill my pump with cold, refrigerated insulin. To always allow analog insulin to stand room temperature for at least a day before injecting or filling pump.


That’s what is confusing. I read that Novolog didn’t crystalize easily and Humalog does but it’s behaving oppositely in my body. I always make sure the insulin is room temp.
The Tandem customer service person said that insulin will crystalize if there’s something wrong with it.
I thought I was doing everything correctly but this makes me feel like I’ve got a lot to learn.
Thank you all for being here to help.

I can not think of a reason it would be the pump or the insulin. I have used Novolog and Humalog with Medtronic pumps and never had that issue. It has to be the infusion set or the manner you are inserting it. Can you try a different type of infusion set with t:slim?

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I’m allergic to the plastic cannula so I can only use the steel one.
Tandem went through all their troubleshooting twice with me and talked among themselves about this and, so far, there is no known solution.
I tested the two infusion sets I used yesterday that caused occlusion alarms and one of them was blocked and with the other cannula, insulin dripped through and wasn’t blocked.
Tandem mentioned that the pump could be at fault but told me to try with fresh Novolog insulin that hadn’t been opened yet.

@Dennis thank you for that information. I don’t recall ever hearing about Humalog crystallizing - very interesting! We never stop learning!

@gtanse I’m sorry to hear about your allergy to the plastic cannulas. I’ve only ever used them and never even tried the steel - it just sounded uncomfortable although people who use them say they’re not (I do still wonder - do they feel cold under your skin in wintertime?).
It actually might be worth your while to try a new pump - since Tandem said that could be the problem you could get a replacement under warranty.
On a side note, in your first post you said your doctorsn’t helping - and thinks the problem is all in your mind. If you’re not happy with them and you don’t feel like they are listening to you and taking your needs seriously don’t be afraid to look for another. We get used to being with a particular physician, but if they aren’t taking us seriously and meeting our needs it may be time to move on. Just a thought.

I can’t feel the steel cannula after it’s inserted. I have had stinging, a few times, right after inserting. I think I may have done something wrong but it didn’t effect the function and didn’t last long.
My Endocrinologist has a non functional office staff that I have trouble communicating with so I do need to find someone else. She was the only doctor accepting new patients at the time and my PCP has given me so many referrals that It caused some fatigue but when I’m motivated by a difficulty like this, I find the strength to continue with the adventure.

I am also allergic to the plastic cannulas and have had to use Trusteel for the 14 years I have been on a pump. I am thin, and I used to sometimes get occlusions from the Trusteel needle being too close to a muscle, I think. I now slightly bend the cannula where it is attached to the tubing. I have switched back and forth between Novolog and Humalog without problems.

One of my sons is T1D and uses the Omnipod. He says he had to wait for his body to adjust to Novolog after his insurance decided to change him from Humalog. I think he had to change to a higher dosage due to hyperglycemia. He hasn’t had occlusions though. When I used Flexpens for MDI, I never had any problems with different insulins. When Novolog has to go through a cannula, it doesn’t work at all.

I don’t know the cause of your problem, however have you ever used another kind of pump? I’ve recently read about cases of people having frequent occlusions with Tandem while having had none with Medtronic. I use Novolog with Medtronic and have not had one in almost 4 years. I’m quite interested to know if many have this issue as I am considering Tandem. The reports I saw indicated that the occlusions are not rare and produce a lot of alarms during the night.

Hi @HighHopes ! I used both Humalog and Novolog when I had a Tandem pump - no problems with either (knock on wood?).

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It has been 24 hrs since I changed to a new cartridge with a fresh supply of Novolog. I don’t use a high dosage so it takes a while to use a whole vial. I don’t know how it could’ve become contaminated. This is a mystery.
I have to continue to watch for an occlusion. A few times it took a few days before occluding and a few times it was just a few hours so I’ll see if it was the insulin in the next few days.
Humalog has always been more stable for me. That’s the opposite of what I expected when I started with this pump.

Tarry @gtanse, in my life, not just in diabetes management, I most often check all areas of possible problem to be certain that I “fix” the failed area.
Have you disconnected the tubing from your trusteel and tried to do a test bolus? And did you get drops totalling the dosage you selected? This will help rule put pump malfunction and/or the possibility that you are somehow kinking your tubing.