Tandem pump - BG stays high for too long before coming down

Tandem T slim: I believe this was discussed before but I have problems with BG going up after eating as expected but staying up for hours before budging downwards. There is enough “insulin on board” so it shouldn’t require a further bolus. It seems to hit a plateau and stay there.

Coming down from the high is more difficult then preventing it in the first place, because we become insulin resistant when high. Also remember, Control-IQ can only auto-bolus 60% of your calculated correction (which is probably inaccurate to begin with given the insulin resistance when high). It sounds to me like you’re not pre-bolusing enough in the first place, but it could be a different setting that needs tweaked. You might need more insulin, or you might just need to bolus sooner before your meal.

It’s normal to have to tweak settings. How do you know you have enough IOB if you’re stuck up in the clouds?

Things you can experiment with that will make Control-IQ more aggressive at bringing down/preventing highs. Listed in no particular order, and your problem might be a combination of more than one of the following:

1 Decrease your insulin:carb ratio. This will give you more insulin up front.

  1. You should be taking your bolus at least 15 minutes before your meal, but you might need even more time than that so your insulin is working before your ingested carbs are spiking.

  2. Inside Control-IQ settings, increase the Total Daily Dose setting. This is one of the parameters that allows the software to change basal rates more aggressively.

  3. Also in the control-iq settings, you can increase your weight. The maximum value is 307 lbs. This is another parameter that sets basal limits.

  4. Inside the timed settings of your personal profiles, you can decrease your correction value (example: changing from 1:50 to 1:47, and consistently trying small changes). This is a big setting for making Control-IQ respond faster, BUT if you make that number too small, it will take you on a wild roller coaster ride, over-correcting at both sides of the spectrum. It can actually drive you into a hypo and rebound into something above target if that setting is TOO low.

  5. Have you tried basal testing yet? It’s possible your root basal settings need tweaked, especially if you’re moving on from a pump with a less accurate delivery mechanism. The syringe-style reservoir pumps are notorious for not delivering exactly what you tell it to.

  6. Even if your basal rates are correct, you can choose to intentionally set them high in timed segments after meals, and trust Control-IQ to suspend any extra insulin you won’t need. Only try this if you’re sure you’ve got the correction factor dialed in to suit your needs, though, as this is the setting that will prevent your hypos from over-insulin delivery. I do this in two hour timed segments after the times I’m most likely to eat (8-10 am and 4:30-6:30 pm, I rarely eat lunch). It allows the pump to be more aggressive at handling post-prandial spikes.

  7. You can also try keeping it in sleep mode all the time, which targets a narrow range of 110-120. But this is a love it or hate it option. I really think this option only works well for people who have good bolusing habits established with this particular pump and have figured out optimal settings, otherwise the pump will seem like it’s misbehaving. You probably don’t have your settings dialed in enough for this one yet, but you could certainly try…


Wait, I just saw the Canada in your name. You’re not using Control-IQ, are you???

In that case, then ignore the Control-IQ specific advice. Sorry for presuming too much, but this is common complaint when making the switch to the T: slim with Control-IQ.

If you’re not using Control-IQ, then I would focus on basal rates, getting your pre-bolus timing down, and maybe needing to lower your insulin:carb ratio (don’t do this if you do eventually come back down to target on your own without adding a correction bolus later).

I had this exact issue when I started tandem and dexcom.
The way I resolved it was to decrease my sensitivity factor. Since control iq depends on that number , it is a double whammy. Your meal bolus is lower than it should be and your corrections and basal are also too low.
On my Minimed pump I was set for 35 on my sensitivity.
I have mine at 25 now and I don’t have the stubborn highs anymore.
My total daily insulin had not changed by much either. Only a few units more. Because I’m not playing catch up on high sugars so often.
Talk to your doctor first, but that’s what worked for me.
My a1c was running mid 6s on Minimed. It went to 5.7 with dexcom. Recently I got. 4.9 and. 5.2. With the dex- tslim so I’m really happy with it now that my settings are good
I also lowered my sensitivity more than I needed to because I wanted lower sugars at night which also helps.

I also had a similar problem recently. I can’t say for sure I have absolutely gotten rid of it but I found pre bolusing helped a large part. The lovely folks on this forum made me realise this in the below thread.

Basically, I’m on novorapid so I wait 20 minutes after bolusing before eating. I use 6mmol (108 mg) as my benchmark. If my sugar is higher than this at bolus time, I wait longer before eating. If lower, I my wait is slightly shorter.

I also started playing with my extended bolus. So I would bolus 80% now and the rest 20% over 2 hours. Helps a bit.

Yes I am in Canada. I have adjusted basal rates, usually have prebolus around 15 to 20 minutes. I will try the insulin:carb ratio.
Thanks for your reply.

The ratio only changes the bolus. The sensitivity is what makes all the difference I think

For Control-IQ, yes, totally agree with that. But the OP is in Canada. They don’t have Control-IQ yet.

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