5. Maintenance Mode: When You're Successfully Looping

When everything goes well and your APS is running, it can feel like you’re flying. If you’re like me, you may get to the point where you wake up in the mornings and only “remember” to check what your BG levels were overnight after you’ve worked your way through reading your email and checking your phone. When you feel like your APS is working well for you and everything clicks, it seems like diabetes is on autopilot compared to the old manual way of doing all of that work.

However, there are still some critical diabetes-related behaviors required for closed looping. After all, when flying, even on auto- pilot mode there’s still a pilot in the cockpit of the plane. Similarly, you’re still in charge of your body, even with an APS on hand.

Some of the basic maintenance behaviors you may be used to if you’re a long-time pump or CGM user. However, don’t be surprised if even long-time pump and CGM users have behaviors that could (and maybe should) be changed when looping.

Pump site hygiene

For example, the length of time you wear your insulin pump site in your body. You may have a habit of wearing your sites for X days. Some people “do ok” wearing them longer than the sites are designed for. However, with a closed loop, it may show you that “doing ok” in manual mode was really not doing as well as you thought, but it was masked by the noise of all the other chaos of manual diabetes mode. With a closed loop, you may have data to show that your pump sites are effective for 2-3 days rather than 4-5-6-etc. With so much other noise taken care of by an APS, the “weak link” remaining in the system (how insulin is delivered into your body) can become more apparent.

CGM sensor lifetimes and calibration hygiene

Additionally, changing and calibrating your CGM sensors (or validating their calibrations) is also a crucial behavior. Many people choose to “restart” and reuse their CGM sensors for a longer period of time. Some of that is out of necessity due to the cost of the sensors, especially if they are self-funded for CGM sensors and must pay cash out of pocket for them. However, many people who start looping, even if they’re self- funded, may find that they no longer want to stretch their sensors as far. The sensor can become less accurate over time. Your diabetes may vary (YDMV), and you do you, but if you’re currently in the camp of restarting sensors 3-4 times, I wouldn't be surprised if you slowly cut back on the number of “restarts” you do for each sensor. When a sensor gets to be near the end of its life, it can have periods of missing data (where you can’t loop), as well as jumpy data. The jumpy CGM data point can cause your APS to oscillate and sometimes overshoot. At best, it can just be annoying. At worst, false and inaccurate data can cause you to get insulin when you didn’t need it - or not get insulin when you did need it.

Remember that your APS is mathematically driven. It takes data in, makes a decision, and sends a command out. If the data in (CGM data in particular) is inaccurate, that therefore influences its calculations, predictions, and decisions.

In most modern APS, you may have a choice of a calibration-free CGM device. It may come factory calibrated. You may want to test and validate your sensors at first to determine if you trust them for automating your insulin delivery uncalibrated. If in doubt, you may want to keep a meter on hand to check your BGs, even with a “calibration-free” CGM. You may also decide the benefits of a more accurate CGM are worth calibrating your CGM periodically.


It’s essential to have a monitoring system in place, no matter which APS you choose. You should still have CGM alarms that work (and will wake you up if needed), with hyperglycemia and hypoglycemia settings, regardless of whether you’re looping or not. However, ideally your APS will also alert you as to whether you are in automated mode or not. This is important for knowing that you’re off “autopilot” and are back in manual diabetes mode.

Body recalibration may occur

Don’t be surprised if you find yourself feeling differently after the first few weeks on an APS. I don’t just mean more well-rested and awake from all the extra sleep you’re likely getting! As you spend more time in range, and less time fluctuating between being high and low, your body will begin recalibrating to this “new normal”.

It’s common to find that the symptoms you might get for a “really high” BG (whatever that might have been for you) might now occur at “moderate high” BG levels. Similarly, some people with hypoglycemia unawareness may find themselves becoming aware of different levels of hypoglycemia, even if they didn’t experience any symptoms before.

This may continue to change over months and years. Think of it as the “boiling frog” analogy, but for your body. When you try to stick a frog in boiling water, it hops out. It’s hot! However, if the frog is in normal temperature water and it eventually warms up to boiling, the frog is less likely to notice the change in temperature.

Similarly, when your body (if you have type 1 like I do) began to be less and less able to produce insulin, it didn’t happen all in one day (most likely). You gradually over time had less and less insulin, and you may have been accustomed to feeling a little bit “off” or “bad” over time until you reached the tipping point or had specific symptoms that caused you to get diagnosed.

So in reverse, as your BGs spend more time in range, your body will get re-accustomed to spending more time in range, and less time in the extreme ends of the blood glucose level spectrum. You’ll also have fewer sharp swings back and forth from the extremes, and so your body will get used to that.

The good news is, you’re having better days and overall better outcomes and likely quality of life. But yes, it is common to feel “worse” at different levels and experience symptoms of hypo- and hyperglycemia differently than before. It’s not just you!

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