Decom G6 sensor reporting false lows 4 hrs after insertion

I’m a new user as this was the 2nd sensor. I am so glad this didn’t happen with the first, or I might’ve lost all confidence in the technology. The insertion felt just like the 1st one, that is really nothing. After the 2 hour warm up it was reporting what was historically correct from the last few days.

Then a the 4 hour mark BG began dropping after my dinner meal. I began treating the lows with glucose. BG would slightly rise and go back to low. Finally I got smart and did finger sticks. There was a discrepancy of some 80 to 100 mg/dl. Also if I put a little pressure on the sensor I could feel a pinch.

I called Dexcom support and got a very helpful tech. He had me stop the sensor, insert a new one and is sending a replacement for the one. When I took the bad one off there was blood around the probe (wire) that had also leaked onto the transmitter. I had a definite lesion, still there this morning.

I was on my stationary bike for 30 minutes to get my BG to drop. I didn’t really want to do a correction using insulin. My ride dropped BG 85mg/dl to 120mg/dl.

As a retired technician who used measuring equipment my whole life a faulty test set was anathema. I am forewarned now. If I get readings and trends that seem odd I will double check with finger sticks first.

I am not just new to CGMs but have been on MDI for less than 50 days.

I have contacted Dexcom support twice, once for app issues and this problem. They have been competent and helpful.

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You acted correctly. I pay great attention to how my body feels and if my CGM gives questionable readings, I check with a finger stick. The g6 is the best we have, but it is not perfect. Good moves on your part.

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Thanks, Willow, I was a little displeased with myself for not checking sooner. I followed the 15/15 rule 3 times before I thought, “This isn’t right.” That’s a lot of glucose.

So glad to hear you got a CGM! I think this is the one piece of new technology that is a life changer!
But with any kind of technology, there can be issues. Going through the search engine here can help you find lots of ways people have come up to overcome some of the first day issues with accuracy.
Some “presoak” the sensor before they switch over. Some just a few hours some the day before, as with all things diabetes, everyone has a different preference.
But as you learned, when in doubt, check. Nothing wrong with checking if not sure.
I will say after using many Medtronic sensors, Dexcom G4’s, Libre sensors, this is the first one that I never check on. I just let it do its thing and it tells the pump what to do. I am very lucky that things just work well for me!
Super happy to hear CGMs are becoming the norm.

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I find that if I have a sensor that is not performing correctly, either sensor errors or giving inaccurate readings when I remove the sensor the wire will be slightly bent in stead of straight. Getting inserted correctly seems to make a big difference to the G6’s accuracy but unfortunately I don’t think this is something we have a lot of control over since it is done automatically. That being said I only have this happen every once in a while.

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Whenever I start a brand new sensor, the very first readings are 40-60 points lower than I am at. If it starts out accurate the drop will occur 2-4 hours later.

For me the ones that drop later have a tendency to be more stubborn about wanting to read too low the first couple of days and need more calibrations.

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@Marie20 I noticed that business about being lower than true for some time after warm up.

I like to pre-soak my sensors for about 12-18 hours. I find that this mitigates the first-day variability I tend to experience without a pre-soak period.

Any CGM number that would mean adding significant insulin or carbs should be confirmed with a fingerstick, especially in the first 24 hours. At least that policy works for me. I admit that I don’t always follow this policy in the middle of the night, but I should.

By the way, I find the 15/15 rule of treating hypos is too much treatment for me. I often treat with 2-4 grams glucose and find it does a good job with little risk of over-reacting and forcing your glucose into an unnecessary swing.

My memory of sensor performance before I pre-soaked, was that some sensors worked well right from the start but that many would falsely go first to one extreme then the other. If I was careful to not over-calibrate and strategically add calibrations when neither the sensor nor my actual glucose was changing rapidly (at the CGM extreme excursion), then I could successfully tame an unruly sensor in the first 12 hours. Oh, and I couldn’t calibrate more than about 25-30 mg/dL or that would really foul up the CGM readings.

I much prefer the presoak tactic now. I only use my sensors for 10 days so I absolutely know that I need to place a sensor on the 9th day of the preceding one.

I’ve also found a connection between wacky CGM readings and evidence of blood on the sensor when I remove it. Not everyone draws this same conclusion. One group I participate in often chime in with “bleeders are readers.” This has not been my experience, however.


@Terry4 By pre-soak you are installing a new sensor for a day before stopping the old and starting the new on the 10th day?

That’s doable.

Yes, I usually insert my new sensor between the 6th to 12th hour of the old sensor’s 9th day. When the old sensor times out at 10 days, the new sensor has been in place for 12-18 hours. I then start the new sensor.

I do ensure that I observe a 30-minute period between the old sensor timing out and starting the new sensor.

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We can all really vary.

Presoak works great for some, but not for others. This last sensor I just put on I presoaked and it was one that started out fairly accurate and dropped hours later and has dropped under what I am by as much as 10-20 points. It now has had several calibrations over the last 48 hours. Hopefully it has fallen into line after this last one.

I don’t always presoak, since I restart mine I don’t always know when a sensor will start going. But I don’t mind being sensorless for 24 hours so I presoak some, it just depends on timing or caring. Sensorless gives me a break from being ocd about reading my numbers lol. So I purposely do that now. My fingers prefer a sensor though!

But I really dislike new sensors, they take so much more work. A restarted sensor for me takes probably two calibrations the first 12-24 hours and a third one to “refine” its accuracy. I’m not saying that’s a set rule, it can vary. But I do know I can’t trust a new sensor at least the first 24-48 hours as they invariably want to read lower than I am at.

I am not happy until a sensor is reading within 5 points regularly. Usually I get about 25 days out of each sensor, although lately half of them have only been lasting 14-18 days.

I rarely have blood, I make sure I don’t press on the applicator at all upon insertion. But when I do it’s a small amount and has not affected my readings.


After insertion I sometimes have bogus readings…high or low. I routinely do a finger test after inserting a new sensor.

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Thanks, @PamS the sensor that I replaced the bloody one started out OK and then got wacky the next day. I did a calibration and it has been good. I think next sensor gets the presoak treatment before starting. It expires on St Joseph’s day the 19th so I may celebrate St. Patrick’s day by inserting then next on while the other continues to work.

For me a new G6 sensor routinely gives a false severe drop that automatically corrects itself within 12 hours. So I just ignore the false lows (check with a fingerstick to see where I really am) and wait for the G6 to start reading right.

The explanation I heard is that inserting the sensor wire causes damage to the tissue (the needle cuts its way in), and the repair of the damage needs energy, which it gets by using up the glucose right there in the interstitial fluid around the sensor. So there’s less glucose for the sensor wire to read which gives a false low reading during the healing process.

After the 2-hour warmup, my last sensor started with an accurate reading, then dropped to LOW within a couple hours, then started rising after 4 hours at LOW and was reading normally a few hours later. I don’t worry about it, I just ignore it and wait. I can see how pre-soaking the sensor could hide this effect because the sensor isn’t started until the tissue repair is mostly all done.

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I don’t pre soak because I restart sensors so …

As a side note, I wouldn’t focus too much on the sensor having been bloody. Sometimes, you just hit something and there’s blood, but the sensor can still be accurate. I’ve had bloody sensors that work fine.

I believe you should, however, go for a light touch with the G6. Double check the instructions, but I think the idea is to gently place the adhesive part against the skin when deploying a new sensor but not to press down against the skin with the contraption that shoots the sensor into you (whatever that thing is called). You can then push the adhesive down more around the sensor with your finger after it’s deployed.
And, as several others have noted, a sensor that starts out bad on the first day may turn out to be good if you wait it out. I don’t believe in calibrating G6s hardly at all, especially not in the beginning, but I think others may have a different view on that.

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Dexcom apparently refers to it as the “applicator”.

During my conversation with a Dexcom cust rep 3 weeks ago to report a sensor jammed in the insertion device, the rep referred to it as the applicator. :man_shrugging: OK, fine.

The people who develop these things always come up with their own terminology. It’s a geek thing, I think. :thinking:

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I realized the best way to handle the G6 after months of experimenting.

First as many mentioned is pre soaking. However I do it differently.
I put a new sensor and I start the sensor with the transmitter at bed time. Then I let it do it’s thing over night. In the morning it’s usually spot on.

But inserting it is the real challenge. I use over tape under my sensor. Then poke through the hole in the tape to get a better anchor.
I peel the adhesive stick to my skin then I pull back instead of pushing down. This pulls the skin away and makes the insertion better and less likely to bend and less likely to hit a vein.

It’s kind of like pinching your skin before giving an injection.
So far I have not had a bad sensor since implementing that.

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