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  • Writer's pictureSheri Colberg, PhD

Follow-Up on Hybrid Closed Loop Systems: My Experience with Looping




In a recent article, I talked about the newest management rage for people with type 1 diabetes called hybrid closed loop systems (HCL). To reiterate my thoughts, the biggest issues with using such a system are that the decisions for insulin dosing rely on continuous glucose monitoring (CGM) readings and coordinated delivery of insulin using a pump via a small plastic catheter under your skin. A recent point in case is the inaccuracy of my CGM overnight last night. It was within the first 24 hours of a new G7 sensor, a time when readings can vary widely. I woke up to an alarm for an “urgent low” at 2:00 AM (it said my glucose was 48 mg/dL), but my blood glucose meter read 83 mg/dL.


What’s more, you still have to fairly accurately estimate the carbohydrate content of your meals and snacks for most HCL systems, along with your insulin sensitivity factor and carb ratios. It’s also a challenge to get insulin levels in your body low enough during exercise in many cases if you don’t plan it out well in advance and make appropriate insulin regimen changes.


After being frustrated with the accuracy (and lasting ability) of my CGM sensors (Dexcom G7), I still decided to try them out with the Omnipod Dash tubeless pump (rather than the newer Omnipod 5 pump) because I knew it was possible to create an HCL with those two devices (the G7 sensors are not yet FDA-approved to work with Omnipod 5). I really wanted to see if I could set up the DIY loop and better manage my blood glucose, even with the devices’ limitations.


The first challenge was becoming an “Apple Developer” to set up the DIY “looping” app using a browser so that it would work on my iPhone. That level of coding is way above my knowledge level, so I found an excellent video online that walked me through all the steps to create the Loop app on my iPhone that coordinates the HCL system with a Dexcom G7 sensor and Omnipod Dash pump. Although it wasn’t too hard to work through, it still took me about 4 hours total over a couple of days to get it set up.


When going back on an insulin pump after taking a pump “vacation” since 2001, I knew there would be a big learning curve to simply pumping again, and I was correct. I used the Omnipod for 12 days without closing the loop to get a better handle on my settings. You still have to be smarter than your pump to come up with basal rate settings, along with carb ratios (the number of carbs covered by a unit of insulin) and insulin sensitivity factors (or ISF, the expected drop in blood glucose from a unit of insulin). I consulted with others to see what theirs are (although mine are very different) to get an idea of whether what I thought those settings should be for me was even feasible. I have updated them several times since starting on the pump. Initially, my time in range (TIR, aiming at 70 to 180 mg/dL) was worse compared to multiple daily injections (MDI) because my pump’s basal rates were covering less of my food intake than when I was using Tresiba to cover my basal needs. Plus, I needed larger boluses to cover anything above my basal needs.


I made all the insulin dosing decisions for my pump for almost two weeks before I went ahead and closed the loop, meaning that I allowed the algorithm (on my phone app) to make changes to both my basal and my bolus insulin dosing based on my entered basal rates, carb ratios, and ISF. On the closed loop, my TIR increased about where I was on MDI (~87%), but about a week into looping, the HCL system gave me way too much insulin two meals in a row (post-dinner and around breakfast the next day), resulting in some really bad lows. In retrospect, I think it just couldn’t adequately compensate for my high insulin sensitivity and usual exercise patterns.


After those very uncomfortable lows, I thought about closing the loop at night only—as the HCL system is excellent at preventing overnight lows that I was often chasing with additional food when using Tresiba, particularly after very active days—and do open looping during the day. I finally compromised by choosing the app setting that allows the algorithm to adjust my basal rates at all times but not give me any boluses. I review the system’s bolus recommendations and change the dosing to compensate for my physical activities (such as walking my puppy post-breakfast most days). I was surprised to see that doing it this way has worked really well for me: no lows at night and a TIR of 95-96% (higher than I was getting with a full open loop or injections) after less than a week of trying it out.


So, based on just my own experiences with this particular “DIY looping” HCL system, I have concluded the following:

  • Having a closed loop at night with the proper settings to avoid all lows (and highs) makes this whole system worth trying. (I’m sleeping better and eating way less at night.)

  • Going back on a pump after using injections for over two decades required a huge learning curve to return to pumping, even bigger than I anticipated.

  • My very low insulin dosing (16-18 units daily) may be making it harder for me to come up with appropriate carb ratios and ISFs for all times of day and night that are applicable every day.

  • I exercise so much—and in different ways and at varying times on subsequent days—that it works better for me to make my own insulin-dosing decisions for meals and correction boluses. That way, I can better adjust for hourly and daily changes in my ISF (which are almost impossible for me to program in without having to change them constantly).

  • Using preset temporary basal rates and higher target blood glucose levels helps with planned (and even unplanned) exercise but is not foolproof for preventing lows.

  • At present, I doubt I will ever feel comfortable going completely closed-loop.


Again, your mileage may vary on an HCL system, and you will want to be open to trying different settings, making adjustments, and benefiting from the full closed-loop system capabilities. After a few weeks, I also tried using a different insulin in my pump (Lyumjev) to see how that works, and I actually like it better than Humalog for pumping (but not for MDI). Like all things related to diabetes management when you are dependent on insulin, it takes trial and error and what works for one person is not likely to work the same way for someone else. Just keep trying until you find what works best for you.

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