New Dexcom site, new sensor, old transmitter, wonky readings

I tried a new location for my Dexcom G6 today - my outer thigh, near my hip. I usually use my outer upper arm, and used my inner upper arm last time with no problem.

Application was fine, but I’ve been getting really wonky readings since the warm up finished 10 hours ago.

I’m in my last 20 days of my transmitter (today is day 90 but I’ve gotten messages saying that it has another 20 day left). This is my first transmitter, so I’m not sure what to expect at the end of its life.

It seems to be that when I sit still, I get a perfectly flat line. Then when I get up and move around, it jumps up significantly.

Even after calibrating numerous times over a few hours, it’s still way off. Sometimes Dexcom is higher than my glucometer, sometimes lower.

Here’s the worst offender so far today. Even before the jump it was way off.

It’s 11pm here and I don’t fancy going through another 2-hour warm up period. I do have spare sensors and a new transmitter I could switch to tomorrow if it’s still acting up. I plan to contact Dexcom tomorrow for a replacement. I’m not sure if they’d replace the sensor or transmitter or both.

I’m looping with my Tandem T:Slim and I think I might turn off CIQ and switch to a less aggressive profile overnight to be safe.

With a new sensor, new site, near-expiry transmitter and not having a hard much experience with Dexcom yet, there are too many variables for me to make sense of.

Does anyone have an inkling if it might be the sensor, transmitter or site that’s the problem? Or maybe it could still get in line in the next 24 hours.


What numbers did you calibrate with?

I have had similar on my current G6 w/ Tandem. I do 2-3 calibrations about 10 minutes apart, and has been working well since.

Each calibration splits the 2 values, so get a gradual correction in about 30 minutes for a wide spread.



Usually calibration fixes sensors for me, but this one is still having issues.

Here are the numbers I calibrated with, all done when I had a side arrow.

Time / Dex / Glucometer
18.00 / 47 / 112
19.00 / 63 / 114
19.40 / 117 / 124
20.30 / 134 / 168
21.45 / 119 / 79
22.00 / 174 / 63
22.30 / 69 / 93
23.00 / 82 / 55
00.15 / 73 / 101

I’m going to give it until early afternoon to see if starts behaving, then report it and swap to a new sensor.

I’m not sure if I should also switch to a new transmitter since this one is on day 91 now and has given messages saying it has 19 days left on it.

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I decided to go back to a site I know works, swap to a new sensor but keep the transmitter and I’ll see how it goes.


@Finn, I don’t have any special site locations, but I think all that really matters is a little bit of “padding” or “cushion” on the site location (calling it “fat” seems rude :grinning:), and a place that you don’t bother too much when sitting or sleeping or whatever.

Outer thigh seems like a good place, as long as there is a little bit of padding there.

I would not give up on it yet. Try it again!


Thanks, @Eric.

I removed the problematic sensor this morning and the new sensor, with the old transmitter in a spot that I know works (inner upper arm) seems to be working fine.

My outer upper thigh (I call it my thigh-hip-butt convergence zone, some may call it a shank) does have ‘padding’ and is comfortable and out of the way. Infusion sets work fine there for me so I was hoping for the same with Dexcom.

I’ll try the site again in the future in case it was the sensor that was faulty. I was really excited about finding a new non-arm site for my Dexcom. Yesterday was so frustrating and I’m glad to have a properly functioning CGM again, especially since hormones make blood sugar difficult to manage at this time of the month.


While the sensor is giving more accurate readings, it does seems to have problems connecting to my pump more frequently.

This has been happening the last week or two (starting around day 80 of the transmitter’s life). The sensor is on my arm and the pump is either on my lap, on my desk or in my pocket, so very nearby. I use 60cm tubing, so it can’t stretch too far away

Is it common for transmitters to have issues connecting as they reach the end of their life?

@Finn, I might give Dexcom a call. They have been able to do a remote assessment for me on transmitter health and have determined when the transmitter is going bad (generally at end of transmitter life). They have always replaced it in this scenario. The only thing that signals this is a wonky sensor, unfortunately. So… keep sensor on, call Dexcom, and see if they can determine health of the transmitter?? Good luck – having patience with this stuff is not easy!!


Thanks, @JessicaD. I’ll give Dexcom a call tomorrow. The transmitter seems to be fine in a new sensor and trusty site, but I need to contact them about the sensor anyway.

When they replaced your transmitter, did they ask you to send the old one back to them? I realise things may be different since I’m in Germany, but I like knowing what to expect. :slight_smile:

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I came across someone who said if they use two sensors consecutively with the same calibration codes, they have issues.

Others have said if you don’t leave 10-30 minutes between ending and starting sensors, they have issues.

My problem sensor and the one before had the same calibration codes AND I ended one and started the other within just a few minutes.

I don’t know why either of those would affect anything, but maybe they played into the issues I experienced yesterday.

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Dexcom thinks this is attempt to reuse a sensor. Usually need 10-15 from end of old to start of new.

But you can remove the transmitter, wait 15-20 minutes, and put transmitter back on same sensor. But sometimes readings are not as accurate unless you do frequent calibrations. Or may get less than 10 additional days.


Cheers @MM2. I’ll keep this in mind next time.

I wish Dexcom would tell us stuff like this (not using sensors with the same codes back-back, and waiting between end and start of sensors if they are the same) in the training. It would prevent a lot of hair from being pulled out.

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Hi @Finn! Sorry for delay – just checking back in here. I am not remembering fully on the transmitter… Dexcom MAY have sent me an envelope to send the transmitter back to them, but I am not sure?! I am remembering sending something back to them once and this may have been it, but I’m not entirely sure! I am sorry! Have you spoken w them already? What was the outcome?

As for sensor timing, I always wait 20 minutes before putting the transmitter into a new sensor and starting it, regardless of code (whether it’s the same or not; or whether I’m restarting a sensor). It has greatly reduced any sensor errors that I get on starting up. :slight_smile:


I had never heard this 20 minute wait suggestion before. I always start them back to back (the G6 wait time is already egregiously long). Maybe next time I’ll try spacing it out. My insertions have gotten easier since I started “tenting” the skin a bit before hitting the button. I’m also not sure if hand-calibrating vs. using the codes makes any difference; I’ve always done the latter.


Thanks @JessicaD . I haven’t actually called them yet. After a few really long, stressful called with Abbott reporting FreeStyle Libre issues (because of Germany language issues, not because of Abbott), I’m avoiding calling Dexcom at all costs.

@needlesandmath I’d never heard of it either and have always started sensors back-to-back. I think I’ll leave a 20 minute gap between them going forward. I’ve also numbered my sensors so I don’t use the same code on two consecutive sensors. It might not matter if I’m waiting 20 minutes anyway, but I figure it can’t hurt.


Sitter consideration for the original site of your outer thigh/shank is compression lows.
I have been using just my arms for a while and if it is on my outer arm, especially as a new start, i can’t sleep on that side without it alarming a serious low. It has to do with circulation.
I wonder if, assuming you are wearing clothes over your “shank” that this might be contributing to the problem.
Just a thought.

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FWIW, I don’t generally wait between sensors, I don’t do the 20 minute delay on purpose.

Sometimes it just happens naturally because I take a shower or whatever. But I have not had any problems doing a quick swap and starting the new sensor.


I never call just use the app contact support. You fill out a few info things then report the discrepancy. I always check please email me back instead of phone call. If it’s acting up after the first day or so they usually send out a new sensor after a day or so without any hassles of explaining the situation.

One can alternatively restart a sensor by stopping it before expiry, sliding a test strip into the slot at narrow end about half way. This breaks the electrical contact, mimicking physical removal. Remove strip after 15-20 minutes, then restart with same sensor code. I often get another 10 days or close to it with respectable readings. Helps to build a stash of sensors against unforeseen mishaps which one can use without Dexcom replacement shipping delay.

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I found removing transmitter easier than inserting strip. Some test strip brands may work better than others.

Removing also lets me clean off the transmitter before re-inserting.

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