Best Steps for Calibrating Medtronic CGM

My biggest pet peeve is when Medtronic’s CGM is badmouthed and hated on. Unfortunately, I take it personally. I have had amazing results with Medtronic’s sensors and I believe most of the outcomes are a direct result from user inputs*. See this post on how I extend my sensors past 6 days.

Very often, I see on instagram that people are simply not calibrating correctly, or not at optimal times. So of course, the sensor will not be accurate. It’s only as accurate as the inputs.

Here’s how I calibrate, which is based on Medtronic’s guidelines:
  1. Step 1: Active Insulin. It doesn’t make sense to calibrate when insulin is still active in your system, as your blood sugar is more than likely moving faster than the sensor can keep up with. Based on my own body, insulin has an impact on my blood sugars for 3 hours. So my last dose needs to be more than 3 hours in the past. Make sure you know your active insulin time and adjust accordingly.
  2. Step 2: Food Impact. This depends on what I last ate, of course, but generally, three hours is okay, unless it’s a high fat meal. Again, it doesn’t make sense to calibrate when there is something actively playing with your blood sugars, so make sure your last meal was 3+ hours in the past.
  3. Step 3: Exercise. Just like food and insulin, exercise can impact blood sugars.
  4. Step 4: As long as the above are in order, I consider calibrating. But I check my current graph and ensure that my blood sugar has been stable for at least 30 minutes prior to calibration.
  5. Step 5: Nearly 3-4 times per day I calibrate following the rules above. If a calibration is needed, but not optimal, I simply wait. Of course this is an inconvenience, but it is necessary for accuracy.

The most important thing to remember, is that accuracy can only happen when the CGM is calibrated correctly. This means, you shouldn’t have insulin on board, food swinging your blood sugars, or recent exercise. When arrows are present, representing a fast change in BG, a calibration is definitely not optimal. Your blood sugar should be stable, flat.

In addition, I make sure that I do not bolus or eat at the same time my CGM is calibrating. Why? Glucose tabs, for example, have nearly an immediate effect on blood sugars. And Fiasp, a new insulin that works 2x as fast as Novolog/Novorapid, could theoretically effect my BGs before my CGM is finished calibrating. Calibration takes between 10-15 minutes. Honestly though, this might be my over-thoughtfulness speaking!

Before you know it, you’ll have a ton of CGM unicorns!

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*Of course I do not actually believe that all sensors are perfect and work 100% like they should. It’s just that too many people complain about their sensors than what would deem FDA acceptable 🙂 If the sensors really were as bad as some people make them out to be, they would have never received the approvals that they have. Rant over.

2 Comments

  1. I just entered a clinical trial on the G670 (Apr 2018) so am new to the Medtronic sensor after being on dexcom G5 and Omnipod. I have to admit that I find inserting, taping and calibrating this sensor quite baffling but will follow your very good guidelines. Oddly enough, I never had to go through such gyrations when calibrating the G5 – all one had to do was not calibrate when there were up/down arrows and follow the G5 recommended high and low variation ranges. Medtronic doesn’t seem to provide such variation ranges that I can find. Regardless – thanks for the great info. I will give it a try as I will be going on automode next week and want to be confident of the CGM readings.

    Liked by 1 person

    1. Hi Jim. I hope you’re acclimating well to your new pump and CGM combo. I will honestly say that I don’t think Medtronic is quite as finical as I maybe made it seem. I wrote this post so that people experience full accuracy with their Medtronic CGM, as MANY calibrate at ridiculous times and expect accuracy. I’m sure if you had good experiences with Dexcom, you’ll do just fine with Medtronic 🙂

      Like

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