Medtronic 780G Insulin Pump showing CGM Graph

How to Deal with a Wonky Medtronic Guardian 4 Sensor

Hello dear readers of “Insulin Pump Life” ?

I’ve written often about how pleased I am with my Medtronic Minimed 780G Insulin Pump. It has far fewer alarms than the older model, the 670G, and does a great job of keeping me in range. However, last night was one of those rare instances where my Medtronic Guardian Sensor (CGM) decided to rebel against my slumber. I thought I’d share my experience and some troubleshooting tips that might come in handy if you ever find yourself in a similar situation.

The 2am Wake-up Call

I usually prefer to “marinate” my sensor; placing it under the skin the night before it’s set to start actively monitoring. This gives the sensor some time to stabilize. But life is unpredictable, and my sensor had a different plan—it quit early.

Marinating is not an official recommendation, but it’s something I learned from the Medtronic Support Group on Facebook to help improve the sensor’s reading on day 1. You just put the new sensor in before you’re ready to use it. You keep the transmitter connected to the old sensor during this time period. The main downside is that the new sensor isn’t waterproof when it’s not attached to the transmitter, so this forbids showering while marinating.

So, I had to put in a new sensor without the luxury of marinating it. All seemed fine, until a rude wake-up call in the middle of the night, courtesy of an urgent low alarm indicating that my blood sugar was “below 50.”

See the above photo of my insulin pump. This graph shows the sudden drop when the false low occurred, and the missing part of the graph is when the sensor wasn’t working.

A False Low

Although I felt fine, alarms like these induce anxiety. First things first, I checked my blood glucose levels with a traditional blood glucose test—it was around 120mg/dL. Perfectly fine. I then attempted to calibrate the sensor, but it refused to accept the calibration and asked me to try again in 15 minutes. Trusting the advice of the ever-reliable Facebook Medtronic Support group, I knew what had to be done. (I re-read Facebook posts about the sensor not working and searched for the same “unable to calibrate” error message.)

Key Findings

  • Calibration Failsafe: If you aren’t able to calibrate your sensor, don’t fret. Turn off the sensor and plan to enable it later—maybe in the morning or a few hours from then. A 15-minute wait may not always cut it. The downside is being in manual mode during this time period. If you need to, work with your healthcare team to get good manual mode settings. Also, you’ll be without a CGM reading while you wait — so you may want to test frequently, and if trending low, have a little something to prevent a low.
  • The Wonky Period: The first 8-12 hours are crucial; sensors can be notoriously “wonky” during this time. If you have the opportunity, always marinate the sensor. It can save you a lot of trouble.
  • Blood Glucose Test: When in doubt, check the accuracy with a traditional blood glucose test, especially if the readings don’t align with how you’re feeling.

After turning off the sensor and going into manual mode, I waited until morning to enable it again. Once re-enabled, it needed a calibration. Thankfully, it complied this time and went back into smart guard mode, working flawlessly since.

Medtronic 780G Insulin Pump on the Device Settings screen showing Sensor enabled
Disable Sensor via Settings => Device Settings. Calibration is required after enabling sensor, but there’s no additional warm up period. You can enable/disable as needed.

The Aftermath: The Importance of Sleep Quality

The disruption may have been brief, but its impact was not. I found it difficult to fall back asleep and was plagued with nightmares about diabetes when I finally did manage to drift off.

Medtronic and other insulin pump manufacturers need to continue improving sensor accuracy, especially during the first 12 hours post-insertion. Whether that’s by making “marinating” a standard practice or finding another solution, the importance of undisturbed sleep cannot be overstated.

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In Conclusion

Living with an insulin pump is far from predictable, but knowing how to troubleshoot sensor issues can make life a bit easier. Always remember to check the facts, stay calm, and consult the hive mind of support groups—you’re not alone in this journey. Here’s to more peaceful nights and accurate sensors.

Sweet dreams, everyone!

About the Author

Lin May has a decade of experience living with LADA diabetes and is the author of Success with LADA Diabetes: Achieving Optimal Health with Diet, Exercise, and Insulin. She is dedicated to helping others learn about diabetes.

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