670G & Guardian 3 Calibration: 6hrs or 12hrs?

I currently use the 670G with the Guardian 3 CGM. The instructions say 6 hours when calibrating after inserting a new sensor, and a maximum of 12 hours between calibrations after that. When I do a calibration, the time given for the next calibration is 12 hours later. But it sometimes changes, at what feels like random times, to a time that is only 6 hours later. What causes this? The only theory I can come up with is when I receive a high or low alert. Another theory might be if the numbers are more inconsistent than the pump wants them to be (although who decides the definition of inconsistent would be unknown). Does anybody know what causes it to chooses 6hrs vs 12hrs?

I have no definitive answer; however, I have the same theory as you. Sometimes, I am requested to calibrate within an hour or two of the first calibration. I believe this occurs when my first calibration uses an elevated BG.

The official answer that the number of hours is determined by three things. 1. The degree of separation between what the sensor thinks and the reading is. The further off the less time between calibrations. 2. The stability of the reading. The more stable the reading over time the more time it will allow to the next calibration. Stability is generally defined by less than 15 points + or -. 3. Fate. Yeah sometimes stuff happens. Ok the fate part is my addition to the pile.

Note: I am a Medtronic ambassador. My opinions are my own. They did not pay me to say nice things. OK, they sent me a shirt and a cup but even I am more expensive than that.

Two days ago I inserted a new sensor and waited the two hours for warm up before calibrating the sensor. Unfortunately, my finger stick came up with 291… Between 9:30 and 12:00, I was asked to calibrate 3 additional times and enter a new BG 6 Times. When my finger stick showed 169 and my sensor showed 76, I removed the sensor, recharged it,
and reinserted it as a new sensor. Everything has been working as expected until now (2 days).

Yeah, I always find it frustrating when I need to do a calibration and I end up being high or low at that time, since it basically means it would not be a good idea to use it for calibration. Sometimes if this happens I actually don’t do the calibration and treat the high or low and wait an hour (or at least half hour) before attempting to calibrate again. It may sometimes mean a little time with no numbers from the CGM, but I guess it’s better to have a little time with no numbers than a lot of time with wrong numbers.

I gave up on using the 670G/Guardian calibration schedule. If I calibrate at 5:30PM when I eat dinner, then my new “670G” alarm clock is going to wake me up 12 hours later at 5:30AM. So … I calibrate at each meal, and then once more at bedtime.

But none of that matters. Because if your BG is stable overnight, your 670G will alert you about that.

The 6 hours is mention in the Calibration section from the manual.

To calibrate, you must use a blood glucose reading from your BG meter and enter that value into your pump. The pump will accept BG meter readings between 40 mg/dL and 400 mg/dL. Your CGM system requires BG meter readings in order to provide you with SG readings. CGM does not eliminate the need for BG meter testing and calibrations are essential for optimal performance from your CGM system.

After inserting a new sensor, a calibration is needed:

  • Within 2 hours after you connect the transmitter to your sensor and start the Warm up period. Your pump will notify you with a > Calibrate now alert when it is ready for its first calibration.
  • Again within 6 hours (first day of inserting sensor only).
  • Again every 12 hours.
  • When the system detects that a calibration is needed for optimal performance.

Yes. Fate. Because the sensor become unstable when you exercise. That’s what the Medtronic rep told me. I had the sensor in my arm, just like the diagram in the manual. He explained that “I was moving my arm too much”. I didn’t make that up.

What you quote from the manual is for when you are inserting a new sensor. I am talking about all times (even after the sensor has been inserted for any amount of time). I could end up doing a calibration at 10:00 pm, and it says I won’t need to calibrate again until 10:00 am (12 hours). But then overnight it changes it’s mind and says I need to calibrate at 4:00 am (6 hours). The point I am trying to make is that what it says at one point might not be what it says later, and I am trying to figure out what determines when it changes it’s mind.

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I have never heard that one. I had mine on while swimming today and it was fine. I do use an additional top bandage. If it does become unstable you might try a Gif’s Grip bandage.

The G3 sensor has a mind of its own. Sometimes it waits 12 hours and smrtimes it requires a BG calibration after 6 hours. BG updates can be required only after 2 hours. I haven’t figured out a pattern yet. Sometimes I just enter the BG shown on my meter and enter a calibration when I return home,

Medtronic is aware of the sensor loop issue and is coming out with a fix shortly by replacing the transmitter with an upgraded one that should fix some of the issues like multiple BG’s and calibrations being required along with those being in minimum or maximum over 2 hours warnings with another BG request and this is according to one of my Medtronic Rep’s I was also told that there are 17 layers within the 670g with only 3 being currently turned on. So in the near future we can expect Bluetooth upgrades to our pumps as well as automatic uploads to Carelink. A new sensor is also coming which will almost eliminate finger sticks so I was told.


That all sounds great! Will we be receiving any kind of notification (as a current 670G, Guardian 3, and Carelink user) when they are available? Also, do you know if the new transmitter will be compatible with the 670G? Either way, thank you for that update, it is good to have something like this to look forward to, thanks!

I would think that Medtronic’s would contact all of the providers who prescribed the 670g just like those on the 630 received priority with getting the 670 and the new sensors. I was told the new sensors are designed for the 670g as a replacement for the problem with the Guardian sensors. And within the next 2 years Medtronics is suppose to be coming out with a sensor that resembles the freestyle libra and that it may only require 1 initial calibration if any at all

I guess all we can do is hope that those upgrades do come ASAP, they sound like one of the things that I’ll be thinking about every day until then (we have our sensors on all day, so I guess it just goes with there being always something there to remind me!). Thank you for the updates!

Just an FYI I am not affiliated with medtronics and I am strickly just a user like the rest of us here. My knowledge comes from a group of 670g pump users who meet with several medtronic Reps every 2 months and voice our complaints and wish’s. Some other thing in the works is an infustion set that will last 1 month before needing to be changed out. Our next Meeting which will be in February will include the engineer who came out with algorithm the 690 uses, so he will get blasted with our dislikes we all have had issues with and I hopefully will be able to pass along some more info on future forthcoming’s

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Yeah. 6 hours in the manual. The tech support rep on the phone this morning says it’s 4 hours. He was quiet when I said the manual said 6 hours. Who should I believe?

I agree that the initial setup is not as described in the manual or what tech support says on the phone. I can’t get Medtronic to acknowledge that reality differs from their statements.

Medtronic reps told me directly, “The sensor can become unstable during vigorous exercise.” He told me that if it becomes unstable during exercise – rapid changes in BG – I should replace the sensor. I said, “I exercise every day”. Silence from the other end.

Fingers crossed.

In general, it should be this:

6 hours after first calibration on new sensor, every 12 hours thereafter.
Max basal has been active for 4 hours, requires calibration.
Min basal for 3-4 hours, requires calibration

Oh, and phase of the moon.

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Has anyone in here received the new transmitter that supposedly ‘solves’ the ‘loop’ problem??? I was told by a Medtronic rep today, that they’ve been shipping.