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This case is interesting to me because of my patient’s fear of hypoglycemia, and as a result she became a fearful boluser. Even on a hybrid closed-loop system, she did not enter her carbohydrates with meals, and if it were not for the Tandem Control-IQ algorithm, her control would have been much, much worse. The other issue I found interesting is how her pump settings (insulin sensitivity factor, the insulin-to-carb ratio, and the basal rate) could have been adjusted better to help her time in range, despite being a fearful boluser.
The Patient
Jasmine is a 50-year-old woman with a 20-year history of type 1 diabetes. She uses a Dexcom G7 CGM and a Tandem Control-IQ insulin pump.
The Problem
Long before she was on any pump, she had several severe hypoglycemic episodes and she became extremely fearful of bolusing before meals. As you can see from her Control-IQ download, her time in range is only 32% with 0% below target, and 68% above 180 mg/dL.
What’s interesting is when you look at how her insulin is given (below), 42% (or 13 units per day) is given as a basal infusion, and 44% (or 13.4 units) is given as an autocorrection by Control-IQ. Only 13% (or 4 units a day) on average are given when Jasmine enters carbs and the system gives her a bolus.
If you look at her data in more detail, you can see that on Wednesday, January 17th she does very well in the fasting state overnight, indicating that her basal rate and sensitivity factors are set correctly. But she eats three meals a day without entering carbs and giving herself a bolus.
The Tandem Control-IQ algorithm increases her basal rate – as shown by the red circle – and you can see from the white dots with the blue squares around them indicated by the arrow that Control-IQ is working very hard giving her over nine autocorrections per day on average. It keeps the post-meal blood sugars at bay despite her eating a meal without blousing on her own.
This pattern continues day after day.
The Solution
Because Jasmine is someone who is afraid to bolus, we decided to make her pump settings more aggressive:
- We improved her insulin sensitivity factor from 1:60 to 1:45, meaning the algorithm will give her more insulin to achieve her goal of 110 mg/dL
- We also changed her insulin-to-carb ratio to 1:15 (1 unit of insulin for every 15g of carbs) for when she does bolus. Her previous insulin-to-carb ratio was 1:20
We wanted to encourage her to really try to bolus, so we asked her to try to enter carbs with her biggest meal of the day as a starting point. When she sees the improvement in her postprandial blood sugars on her own, hopefully she’ll consider giving herself more boluses.
The Takeaway
The overall lesson here is that hybrid closed-loop systems like the Tandem Control-IQ are called hybrid closed-loop for a reason – you still have to enter boluses (by entering carbs) for meals. They have modulating basal rates (in this case the basal rates went up tremendously) but when the algorithm predicts that the basal rate is not enough to control the postprandial blood sugar, it will give an autocorrection bolus in addition. In this case, Control-IQ did a pretty good job, considering Jasmine was not blousing for meals at all, and she did not restrict her carbohydrates.
The key for this patient though will be to alleviate her fear of hypoglycemia, which may involve seeing a diabetes therapist like Dr. Bill Polonsky or Susan Guzman at the Behavioral Diabetes Institute.
This is me too although my TIR is about 85% ( but my CGM is set higher at night because I hate nighttime lows! I am on Dexcom G6 and had a bad Omnipod experience so I’m not on a pump (71 years old & T1/T2 for about 25 years). I recently went to CeQur Simplicity insulin patch so I can deliver a 2 unit bolts as needed. This has been perfect for my needs. I catch the highs quicker & plan better for meals. Never quite perfect but much better.
That’s awesome! Sounds like you found the system that works well for your needs.
This is me, except that I don’t use a pump. Yesterday, my b.g. was firmly ensconced in the red zone (around 15 mmol), with no sign of it dropping, according to my Freestyle Libre 2 sensor. So, I gave myself 2 units of trurapi. My b.g. dropped quickly to 2.7 mmol, and I panicked. That’s so close to coma range. So, I started eating candy (without enjoying it). It took around 45 minutes for my b.g. level to return to the green zone, but then it spiked to 22. I’m so afraid of hypos! I’m a low carber (between 10 and 20 per meal, plus low carb snacks like nuts). Bolusing 1 unit per 20 g isn’t sufficient for me though. My plan is to more closely monitor my intake of carbs and try to bolus 1 unit per 15 g. Doing so right before a meal doesn’t prevent spikes though. I’ve been told to not bolus 10-15 minutes before a meal with trurapi. Any suggestions? (THANKS SO MUCH IN ADVANCE FROM A CANADIAN FAN.)
You should avoid giving yourself boluses – like of two units – because with a pen it’s not as accurate, and if you only need two units you can just skip it and follow your blood sugars. Its very hard to get tight control on multiple daily injections. I know you don’t want a pump, but you should not rule it out because they’re getting better and better.
Very good read! I am a Type 1 on the Tandem Mobi and use the G7. I had an esophagectomy to cure my esophageal cancer in 2022. Because of the surgery, I never know exactly how much I can eat at a time, and if I dropped low, my options became limited, as I really couldn’t always eat additional carbs. So, as you can imagine, I too had an issue with pre-meal bolusing. Thankfully, my endo is super patient and has worked with me to develop a very similar approach. We tightened my ISF and I pre-bolus for 1/2 of what I’m going to eat. Then, if I eat it all, I bolus to cover the rest. Also, if I’m having a bad day with being able to eat, I pre-bolus for 1/4. This has worked well so far – this new plan started in December. I’m so thankful for the Tandem Control IQ and endos who care about their patients!