670g sensor nightmare

I have been T1 for 48 years, 4+ w/an Animas pump and Dexcom CGM. I switched to the 670g in January. It’s supposed to be the best, but I can’t say, because the sensor performance is so bad. At this point, I am trying to return the 670g and get it refunded to my insurance, then maybe get a Tandem pump and go back to Dexcom for the CGM. Has anyone else had this kind of sensor nightmare issue with Medtronic?

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Hi Andrew @AndyMS, I see you are a really new member here, 22 minutes, so let me offer you a Welcome to TypeOneNation Forum!!!

Being new here, you probably haven’t read the MANY posts about the 670G. Rather than initiating a new Topic “string”, I suggest that you might use the search option at the top and see what you find.
You are not alone.


I gathered there were problems with the 670g; many seem to differ from mine, but it looks like there are some similar ones. I just can’t believe this thing made it to market in its current state.

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@AndyMS, from what I’ve been told, the 670 G with its matched glucose sensor is awesome in all respects. I have been with people, all ages, who use it and are extremely satisfied - and this includes a couple of teens who were part of the trial to get the system approved for under age 16.
The reason it worked so well for the people I mention is that none of them looked at the device a “Plug 'n Play” but rather let it learn each body; they also read the User Manual.

I did indeed read the manuals.

The problem has been, very specifically, the Guardian 3 sensors that th 670g relies on for SG readings. These will often fail (go into “updating sensor” mode) after two or three days, which is typically followed by a message that the pump is falling back to programmed mode, then three hours later by the “replace sensor” message.

I have also had one sensor fall off seconds after insertion (never got to the transmitter) due to bad adhesive, and one where the needle bent on insertion, meaning that I had to sacrifice that particular sensor since the needle couldn’t retract. Add in the ones that tell me my BG is <50 and dropping (when multiple external meters tell me 100 and rising) and there are problems.

All of these problems are aggravated by the fact that if you should be away from home and need to replace a sensor, you can’t just carry a spare sensor. you also need to carry around the “Serter” and extra adhesives. This is in sharp contrast to the Dexcom sensors (I used G4) that come complete with a disposable insertion device. There’s much less to lose.

I understand that the 670g has to “learn,” but in order to do that, the sensors have to be durable and reliable–but they’re not.

In my experience (which may be onlymy experience) Guardian 3s have nowhere near the reliability of the Dexcom sensors. I also think that there are some physical design problems with the sensors: Seriously–you insert a small, flexible wire beneath the skin, but to attach the transmitter, you need to apply substantial force at 90 degrees to the insertion site, which is asking for trouble. And you place the sensor on a tiny adhesive pad, and attach a much more massive transmitter to it (thus the requirement for extra adhesive tapes). IMO, Dexcom’s approach (placing the sensor at the center of a large adhesive patch and bracing it with the transmitter mount, then attaching the transmitter with a downward motion) is a significantly better thought-out design.

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I had a lot of the same issues and had switched from dexcom to the 670g as well…it was a hard transition for all the reasons you mentioned. I spent a lot of time with the Medtronic trainer and the support people on the phone. That ended up resolving my trouble inserting the sensor (I now use primarily my arm and thigh because it inserts better…I am thin but have a lot of floppy abdominal tissue from being pregnant with twins). It requires a lot of patience and savvy about knowing when to ignore the calibration/enter BG messages that the sensor prompts you with. For a while, every time it promoted me when I wasn’t expecting it or malfunctioned, I called Medtronic and they really did help me make sense of it. Now, I’m really happy with the 670G. It is by no means an artificial pancreases, but I was having a ton of lows and no hypoglycemic awareness, so for me, the dramatic reduction in hypoglycemia without a corresponding loss of overall tight control has been a game changer.

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It’s good to hear that they were able to resolve things. I’m working on it now…but having been awakened several times at 2-3 AM the day of a trial to find the sensor crapping out (I’m an attorney) I remain very close to throwing the stupid thing out the window. Right now, with this device, I feel far less in control of my diabetes than I have at any time in the past 48 years.

I’ll see if they can figure out what’s going wrong with the sensors (I also thigh-mount the sensor and infusion set–3" apart because that area interferes least with my life).

Unfortunately, I still have nighttime issues with the sensor. It doesn’t fail or crimp at night, it just likes to remind me that it’s there…at times it feels like we have a newborn again.

Is your main problem that the sensor fails/crimps, that it’s inaccurate, or that it continually asks for more BG or calibrations…or some combination thereof?

Like I said, it’s no magic bullet and I think each person has to decide if the risk/benefit ratio is acceptable to them. For me, because of my hypoglycemic unawareness, automode has changed my life. But if I were getting the 670G in order to make management easier, or with the hope that it would dramatically lower my A1c…it wouldn’t be worth it.

I haven’t heard the term “crimp” before, but perhaps. I’ll get an alarm, typically the “sensor updating/up to 3 hours” repeatedly, then a notice that the sensor needs to be replaced. That’s no good.

I also have some hypoglycemic unawareness (never thought I’d actually miss the feeling!) and so I note that there’s an insulin cutoff mode that doesn’t require full-on auto on the pump. Unfortunately, that also uses the sensors, so when they go bad, there’s nothing you can do.

I got the 670g because it was highly recommended when Animas announced their end of life. On the Animas, I had sub-6 A1c readings and my endocrinologist thought those were too low. I’ll bet I’m well over 6 with this sucker… :frowning:

Usually I get those sensor updating messages for one of two reasons:
-the sensor is about to expire (each sensor session lasts about a week, I find that I get this error message towards the end of my week, and my BG readings can be a little off)
-I have entered too many BG from my meter. This is a hard adjustment from the Dexcom, which didn’t care how many times you calibrated it in a day and didn’t ever prompt you for a BG unless it actually needed it. However, there is a problem with the 670G software…if you enter a BG or calibrate too often, it will start rejecting your BG, but ask for more BG, or go into this sensor updating mode…so you can’t reliably follow the prompts you will get for more BG or calibration. It truly only wants to be calibrated twice in a 24 hour period, and if you exceed that, things start to devolve. This is where technical support was really helpful to me. If there is a discrepancy between your meter reading and the sensor (this is particularly common at the beginning of a new sensor session), then it will reject your calibration. The problem is, it will as for another BG…DON"T DO IT…you must wait at least an hour to re-enter another BG…and even longer to recalibrate. At Medtronic they can tell you exactly how much of a discrepancy will kick you into this vicious cycle (I had it written down but lost it). Bottom line is, you can’t follow the prompts uncritically. This was a source of a lot of frustration for me…but over time, I’ve figured out how to play by the underlying rules of the game.

Also, I typically only put on a new sensor first thing in the morning and I fast for the first two hours that it is in ‘warm up’ mode so that when I enter the first BG and calibration, I am not trending up/down. I find that if I do a calibration or enter a BG in a time of BG transition (ie after a meal, dawn phenomena, stress), there is more likely to be a large discrepancy between the sensor reading and the meter reading and that throws you into the vicious cycle described above.

My guess is that a few sessions with the folks at Medtronic on the phone will clear up a lot of the confusion.

The crimping happened for me when I used my abdomen, the fiber would dislodge and crimp…but as I mentioned before, that’s because of my body habitus post-twin pregnancy.

I also had a lot of problems with the Guardian 3 sensors. I switched to the Dexcom 5 sensors since I’m on Medicare and they’re wonderful compared to the Guardian sensors. IWAS well trained before starting the 670 pump and I have a science background. Many others have had problems with the sensors. I have kept the 670 pump and use it in manual mode since I am not eligible for a new pump. Manual mode works well.

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Hi Andrew
I too have had type 1 for 48 years
I also had ,any many issues with the Medtronic guardian 3 sensors until someone on this blog suggested I try it in my leg. I put it in my upper thigh area and it is very comfortable and easy to maintain.
I have not had a failure since last December and only a few sensor updating issues. I find it fairly accurate most of the time.

I don’t use auto-mode all the time. I don’t find it very helpful. Having the use of duel and square wave bolus is a key for me

I am considering changing to Dexcom to eliminate all of the calibrations but also hoping that Medtronic can correct the continuous need for calibrating and can integrate the sensor glucose value into the pump as the bolus value
I understand your frustration.

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That’s the sort of thing I’m considering at this point. I do like the insulin cutoff, but the rest of auto mode seems less than ideal.

I also have been T1 for 56 years.I love my pump 670g,but I don’t like any of the senors.I can still feel my symptoms most of the time.I test around 4 times a day. The sensors can be a nightmare

I have read many similar complaints in a Medtronic 670 support group on Facebook. I saw these complaints about the sensors and decided not to use that pump. In 2017 I started using the Medtronic 630, without the sensor. I am very happy using the Dexcom G5, even though that requires my using a separate receiver. There are many people in the Tandem pump group who say they stopped using the Medtronic pumps because of the unreliable sensors. They are happy with the Tandem pump that is integrated with the Dexcom. My next pump will be the Tandem.

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Hi Andy,
I have also had diabetes for 49 years. I have been a Medtronic pump user for a very long time. I have the 670G. I know there was a problem with the sensor. I called the 24 hr. hotline and they replaced mine. Try calling and please don’t get discouraged. I love the 670G. Did you meet with a trainer? Mine was a big help. Good Luck.

I did the same as Marie, changing to the Dexcom G5 since the Guardian 3 sensors were not covered by Medicare (or Medicare Advantage). I am very happy with the Dexcom. The 670G still works fine in manual mode, so until I can switch to a Tandem pump under Medicare, this combination is (to my surprise) working better for me than the 670G Automode.
I’m a 51-year T1D and have never had such good control, and with such relative ease. I’m very grateful for the technological advances.

My issues with the Guardian sensors seem to come in waves. In the past few weeks, I had been on the phone once or twice a week with Medtronic about replacing defective sensors. I just learned that now you can do this online at www.medtronicdiabetes.com, click on “store” and you will find a place for returns. I just went through a box of 5 sensors, and all of them worked a full 7 days; this is an exception. Yesterday I had three sensors in a row fall out of my arm the second I inserted them; I placed the fourth one on my abdomen and it seems fine so far. And Medtronic is replacing the three defective ones.

Despite all of this, I’ve had the lowest A1Cs ever on the pump; in the past six months, they have been 6.8 and 6.7; I’ve NEVER been below 7 in the past 45 years. I also had hypoglycemic unawareness; with the pump it’s no longer an issue. Just wish they’d fix those sensors.

I’ve only ever had one fall off…I have had another where the insertion needle bend, so it’s impossible to withdraw (THAT was fun to remove). Mostly my issue has to do with all the alarms (many of which are, when I check BG with a finger pricek, shown to be incorrect) and the early failures. Without a reliable CGM, it doesn’t matter how good the programming in the pump is. As I’ve said elsewhere, this feels like the most out-of-control I’ve ever been.

I have had T1D for 55 years and been on the 670G for two years. I have had several abdominal surgeries, including a kidney transplant. Thus there is a lot of scar tissue there (and no belly button), so inserting the sensor in my abdomen can be problematic. I live alone so inserting the sensor in my arm is impossible for me. I then tried my thighs, but it would either bleed profusely, fall off, or bend the sensor filament. Then my pump trainer suggested I insert the sensor just below the very, very bottom of my sternum, making sure to not insert into the bone, but rather in the soft tissue at the top of the abdomen just below the chest. Since doing so, my sensor values have been nearly identical to my bg results. It has been a magnificent improvement and is quite comfortable and “out of the way”, albeit rather odd looking when I’m not wearing a shirt, such as when swimming (I’m a guy obviously). You might want to discuss this with your trainer or medical provider.