Need advice on starting new sensor sessions

Hi Everyone,
I’ve been using Dexcom G6 and Tandem T:slim pump for several years now but recently have had a run of sensor calibration issues after I start a new sensor session. I’ve called Dexcom and Tandem to try and sort out best practices for starting a sensor and whether you should end session, enter code and start session on the pump first or on the G6 first, or on both? It seems like no matter what I do I end up having to calibrate right after a start-up or once a day for 10 days. I’ve received advice to wait at least 10 minutes after ending a session before starting a new one. At this point I’m so confused that I feel like I’m back to square one when I first used this technology. Any advice? Thank you.

1 Like

according to Tandem, if you start the sensor with the code on your phone you do NOT have to enter it on the pump (use “skip”)

I have heard others complain that if they start the sensor on the phone and use the “photo” QR code method, they they experience this calibration thing. I always use the QR code, never had an issue, but I have heard other people’s outcomes can be different.

how about you try to start the sensor on a phone, and manually enter the code instead of the QR code. .Then on the pump you start the sensor and hit “Skip” when it asks for the code. You didn’t say what you are dong now so if that’s exactly what you are doing now then sorry to reiterate. good luck.

Diane @DFBB, I have been using the t-Slim and G6 for CIQ since it became available and have not ever had a “calibration issue”.

In that the t-Slim pump is the principal receiver for CGM values, and the phone is classified “secondary”, because there can be only one designated “receiver”. I always use the pump to start each new sensor session; the phone catches up after a few minutes. And I’ve never been asked to calibrate; actually, Dexcom advises to not attempt a calibration within the first 12-24 hours.

A [there may be other reasons] reason the phone and pump do not start immediately together is that their signals are not often simultaneous. Someday when your glucose levels are changing rapidly such as when an up or down arrow is present, put your pump and phone side-by-side and watch the SG values - you may see one of the one of the values change up to 5 minutes before the other. As another aside, during the 4 years I’ve the G6 I haven’t needed to calibrate a dozen sensors. Basically, and statistically, the reading sent by a G6 is more accurate than any fingerstick BG; so I hesitate using a less accurate reading to calibrate the more accurate sensor.

Thank you both. Just to be sure that I understand, if I start a new sensor session on pump do I first stop it on the pump as well? I think I’ve been jumping around too much between pump and phone and have created more confusion for myself. Now, I’ve been stopping sensor on the phone and then the pump, starting it on phone, entering code, then going to pump, starting but skipping code. I think this is my problem?

Diane @DFBB, are you putting on a new sensor before the existing one expires, of do you wait for the old to expire?

Except for unusual times, like earlier this month when I needed to slide “gracefully” into an MRI tube, I let the old sensor expire normally on my pump. My phone usually beeps while I’m preparing the new sensor telling me to “replace sensor” - I rarely need to ask either device to stop. A few times I’ve noticed the phone didn’t immediately recognize the new sensor - but it always did within 10 minutes without me needing to do anything - and it recognized the elapsed warm-up time correctly.

full disclosure @DFBB I am only reading the tandem manual because I like their new tiny pump. - I’d go with @Dennis solution which is (paraphrasing) start, stop and enter the code on the pump. A follow-up @dennis, is what do you do with the phone? I’ve jump started an existing session on my phone but I started that session on my phone? now I’m confused =)

1 Like

I have generally stopped the sensor a few minutes before it expires, so I am going to try and wait until I get the alert that it has expired before changing it. Next time around I’m going to try and do everything on pump and let the phone catch up. Phew, who would have thought changing sensors and transmitters are confusing. Thank you all for your advice.


I agree with Dennis. I have always replaced our daughter’s sensor using the Tandem pump. When I stop the session on the pump, I also stop the session on our daughter’s phone (although maybe that hasn’t been necessary). Other than that, I do nothing with the phone. It always catches up with the pump.

Dianne @DFBB, this morning I had a scheduled 10-day sensor activity scheduled and wanting to share with you I kept “special” alertness - here it is.

My sensor expiration notice appeared on my pump while I was still nursing a cup of coffee on the lanai and the Dexcom notice on my phone had not yet appeared. I left my phone outside and went into the kitchen - 40 feet away - and replaced and started a new sensor [touching only my pump. While grabbing a fresh coffee before going near my phone my wife wanted me to listen on the land-line speaker phone keeping me from checking Dexcom on my phone. Later when I went back outside, I looked at my mobile and the message stated 1 hour 48 minutes warm-up remaining.

This kind of confirmed that what I previously wrote, we do not need to physically “sensor start” on multiple - Putting the simple 4-digit code in on the pump updates everything - including the G6 reading on my watch - everything immediately in-sync.

1 Like

Thanks for that @Dennis it’s a bit unclear on the tandem literature.

I agree with @Dennis said and want to add

  • If you use your phone to start a sensor the pump will be updated by the Dexcom transmitter. It is easier to start new sensors using the Dexcom app than on the pump
  • When changing the Dexcom transmitter you need to complete the process of entering a transmitter serial number and starting a new sensor on one device and wait until that device successfully pairs with the new transmitter. Then only enter the new transmitter serial number on the other device.

@MarkCK reports the T:slim doesn’t say the Dexcom transmitter is expired at the end of a transmitter’s last sensor session. The Dexcom app boldly prompts to use a new transmitter.

I’ve been using the G6 & Tandem system since they became available. I’ve only had a few minor glitches with one sensor requiring recalibration at least once a day if not more. That’s been the total of my glitches since the beginning…My guess is it’s your pump. You need to talk to Tandem and get someone who actually listens and understands. Suggest you start off asking to speak to a supervisor & take names. With the amount they charge, you should be totally satisfied with their equipment. Again…Their Equipment.

In addition, you do get weekly warnings that your transmitter will soon expire, starting 3 weeks or so prior. It’s easy for me to dismiss them without reading the details as I think it’s a glucose alert.
I’ve read enough to see that the transmitter will expire soon, but couldn’t catch the details about how much time is left, and if there’s a way to retrieve it in history I haven’t found it.

Dennis, I was a little startled to read that you feel the G6 reading is “more accurate” than a fingerstick BG. I was under the impression that the BG value was the golden parameter, that the G6 provides something that is related to that, but doesn’t measure it directly, and that the BG is what we’re really concerned with.
Or did you mean the BG values varied more than the G6 values? That would be a measure of precision, which is different from accuracy.
I suspect I’m way off base here, and don’t really understand what you’re saying (WBTFT: wouldn’t be the first time :slight_smile: ).

1 Like

Keith @khjalmarj, the finger-stick meters measure glucose levels from capillary blood [unlike the more accurate lab-test using blood from a vein] and the continuous sensor reads body glucose levels from interstitial fluids - IMO, knowing the level of glucose that may be causing harm to my body cells is more important. As a point of interest, the US FDA had never Approved for insulin dosing any device before the Dexcom G6; no meters have achieved this level of accuracy.

Third party evaluation of glucose accuracy is based on MARD ratings [explaining MARD is way, way above my pay-grade, but has something to do with mean differences and is gold-standard for science folks] which compares the device readings to lab values.

@khjalmarj testing our blood at home using fingersticks first became available around the early 1980s (as best I recall - I started doing them about the time I graduated from college). Blood glucose could be tested in a lab prior to that, but that was for “professional use only” - not to mention that getting results took days and was expensive.
Since meters have been around longer than CGMs it’s not surprising that some see them as the gold standard - and they may be more accessible and less expensive for some users. But as much as I appreciate the value of “old school” technology there are advantages to the new. And if the only reason standard BG meters are considered the benchmark is that they were made first, that does beg the question “Why?” or “Is that reason good enough?”

Thank you to everyone for such great advice. I do appreciate the tips and tricks.