Inaccuracy at Night

During the day, Dex tracks my sugars quite well. But I’ve never really had a problem with sugars during the day, since I test so often. I mostly started on Dex so that I could prevent overnight lows and highs (I have mild gastroparesis, so it’s really hard to predict what’ll happen with overnight bg’s), and it seems my readings are way off at night. I can be in the 200’s and Dex will tell me I’m only in the 150’s, and I can be in the 40’s with Dex reading in the 60’s. These aren’t fast rises or drops either.

I’ve tried clipping the receiver right next to the sensor, making sure I didn’t roll over onto the sensor, nothing seems to help. Now I’m considering changing my high/low alarms from 60/160 to 80/140, which I’m sure will alarm frequently and wake me up throughout the night, but I’m frustrated and at a loss for what else to do to catch the highs and lows in time.

Have any of you had this problem? Anyone have any tips I haven’t thought of?

Where are you wearing your sensor? I know I’ve probably asked you that before, but I suck, so please remind me :wink:

Dex is really good (almost too good) at catching my overnight highs. I’ve lost many hours of sleep thanks to its incessant beeping. I wear my sensor either on my arm, or on my butt. I’m a side/stomach sleeper, and I rarely get transmission interruptions. My low/high alarms are set for 70/180.

I know that you received the receiver through a kind donation from a friend (with a doc’s Rx, so back off legal folks!), but did you buy a new transmitter? Is it possible that it’s going kaput? I think it’s warrantied (is that a word?) for a year or so, but after that, all bets are off. Just a thought.

I hope you get it straightened out. Even though I complain about it, without my Dex, I feel so vulnerable.

My first thoughts are that Dex is best in “normal” range. Everything else seems to get shifted towards normal so it doesn’t overly surprise me that for high sugars you tend to see lower readings and for low sugars you tend to see higher readings. With that said, the Dex should be following your trends fairly closely so you should get a warning as you leave “normal” range and be able to start taking steps to correct it. My Dex is usually spot on between about 60 and 175 and then starts to get a bit off as I go lower / higher. Since my warnings are set at 80/120 this is fine for me. Is it off when your sugars get way off during the day too? If it’s just at night I don’t know what to tell you, but this sounds like it’s a problem that should be happening all the time. Especially if all of your calibrations are within range it’s not unusual for it to be off at extremes.

Are your daytime numbers in close agreement with your meter? If so, the transmitter may be OK. If not, then the transmitter may need replaced, ilike Shannon suggested. I am asuming the transmitter is a year or more old. A new transmitter costs $300+ if you have to pay for it yourself, but if it is a year old your insurance should pay for it.

If your sensor is on your side or on any part of your body where it is pressed between your body and the mattress, then that can cause inaccurate numbers. this was happening to me for my first three sensors. I have a heavier body than you probably do and i had terrible numbers while sleeping. Now I have my sensor close to the middle of my abdomen, but not too close to my navel, so that it never gets squished. My numbers at night are very good now!

Thanks so much for your responses. I think the transmitter’s still okay, since it works pretty well when I’m in normal range…the trending works well too. I’ve only seen the problems with the lows and highs, which is unfortunate since that’s when I need it most. Shannon, I’m wearing the sensor on my belly now, but I’m planning to move it to my butt next, like you suggested a few days ago. (Worried about sleeping on it, though, since I’m a back sleeper.)

Maybe the problem’s like Rebecca said, not a nighttime only issue, but that the sensor only works well for me when I’m in normal range. During the day I’m almost always between 60 and 150, so I’m only seeing the big inaccuracies at night. Which means I’ll probably have to lower/raise my alarms like yours, Rebecca. We’ll see how often the alarms go off!

I’m just surprised the numbers would be SO far off. In the time I’ve been wearing the sensor I’ve seen numbers below 55, but never had it register a number over 180, even when my bg’s significantly higher…I’m pretty sure that’s not the way things are supposed to work. :frowning:

Very strange. Mine has no problem keeping up with highs and lows (in fact, current reading is 243 mg/dl and a finger stick confirmed with a reading of 238 mg/dl - ugh!)

I totally remember that conversation now (my mind is all over the place today, sorry). Your husband is going to help you put it on, right (I think you told me he was “squeamish about needles”)?

Don’t worry about sleeping on it. I have a Pod (much larger than Dex) on my butt right now, and it doesn’t bother me when I’m laying down (or sitting)! Just be careful when putting on and taking off clothing. I use Skin Tac around the edges to keep it stuck longer, and I usually end up having to pry it off.

I really hope you get it sorted out - that’s the whole point of the Dex, right? To stay on top of highs and lows?

Yup, and that’s why I’m frustrated! I guess I’ll see if a different site works better. I wasn’t really worried about it hurting to roll over on the sensor, I’m on the pod too and it’s rarely a problem. Mostly worried about what Richard’s saying, that the data gets more inaccurate when the transmitter is squished…Worth a try, though, for sure.

(And yeah, Jer’s agreed to help me with insertion, even if he has to close his eyes and bite his tongue. Kind of ironic that I’m married to a man squeamish about needles.)

I haven’t encountered Richard’s problems with the squished transmitter at all. In fact, I often sleep with my head on my arm (which is under the pillow - kind of hard to explain), and I rarely lose connectivity to the receiver and my data is good (I still test every time I wake up at night).

I guess, as with everything else, YDMV.

Poor, Jerry :frowning: I can remember going out with guys who were totally freaked out by the “needle thing.” Thankfully, Brian was ok with it. Good luck to you both!

Why do you keep posting that people who have actual, real-world experience with something shouldn’t be giving out advice? Seriously, I don’t understand. I’ve learned far more from other users of products than I ever have from the so-called “experts.”

You are missing the entire point of this community: to share experiences to help and learn from one another. If you look through the forums, the posts are all about members helping other members through their personal experiences. Why are you so opposed to that?

And, BTW, asking for advice is not the same as asking for a problem to be fixed. Elizabeth didn’t ask anyone to “fix” her Dexcom problem, she only asked if anyone had experienced similar issues. That’s not even remotely similar to “asking a plumber to fix an electrical problem.”

Finally, I don’t know who you’re talking to when you call customer support for these issues, but in all my years of having diabetes and using diabetes technology, I’ve NEVER gotten technical support from a doctor, nurse, or other diabetic. Do you have a secret phone number or something?

Hi Elizabeth

I’ve experienced similar, but kind of on an opposite spectrum. My numbers are fantastic during the day, but when I’m sleeping, the Dex will sometimes alert me that I’m in the 40s when I’m really at 70. Or sometimes it’ll read that I’m at 350 when I’m really at 220.

It does say in the manuals that the Dex is mostly accurate when you are in your target range. Outside of target range, it starts to get off the higher and lower that you go. Mine is set at 60/160. I put the sensor on my abdomen (you can see pix on my page) and I put the sensor on a wooden table next to me while I’m sleeping. Because it’s on the wooden table, when it vibrates it practically shakes the whole house! haha.

As far as getting better accuracy, maybe you can callibrate right before you go to bed? I don’t know if you’re already doing that… but I’m sort of looking for a resolution to this issue as well. haha.
Sorry, thinking out loud.

Thanks! I’ve actually been keeping the receiver either clipped to pajama bottoms or in a sweatshirt pocket, so I don’t think distance is a problem. Interestingly, last night the problem was more like what you’re seeing. It kept alarming to tell me I was low (once with the under 55 alarm!) and each time I tested I was actually between 99 and 104. I was this close to throwing the thing across the room and stomping on it!

I also noticed reviewing the readings that they were trending higher around the time I sat up to test, then dropping lower again within an hour. Which makes me think something weird is going on, either with the transmitter bouncing around (although this isn’t a problem during the day, so I doubt it), or with ISF settling so the readings become less accurate. That’s what I’m guessing the issue’s been all along, since I’m a pretty heavy sleeper and I don’t move much. Maybe I need to start flailing around more in my sleep. :slight_smile:

Ooh, good point. I’m a big tosser/turner, so there’s always lots of movement going on.

Yeah, I have to agree with Shannon. I’ve learned more from other diabetics than I ever learned from my endo or CDE, because they only have the limited experience of whatever their patients have told them. People who’ve actually been there can give much more relevant guidance. And with all the people in these forums, you’re bound to hit on people going through the exact same issues.

I understand why you’d be concerned with trusting “non-pros,” Rita, but IMO we’re all pros from having actually lived through this for however many years. The few times I’ve called help lines I’ve gotten absolutely nothing valuable. For example, a few years ago I kept calling Insulet (OmniPod) to tell them my sugars were spiking after every site change. The rep helping me, who also happened to be a t1 OmniPod user, said he’d never heard of that happening, and he just recommended I push down harder on the Pod during insertion. Which of course didn’t help, so I brought the problem to the DOC, and heard from so many other people who were having the same problem, and had solutions on how they’d dealt with it. If I hadn’t asked, I probably would’ve given up on pumping.

I love everybody here, how willing everybody is to jump in and try to help. The people in the DOC actually CARE about each other, which is a lot more than I can say about people who’re paid to help…

That used to happen to me too, before I started doing a very careful job with starting up a new sensor. I find that if I insert the sensor at least 3 or 4 hours before I fire it up, and be very careful to calibrate when I am TRULY stable in bG, I get really good accuracy, day and night. I must admit, it took me at least 8 sensors worth of time to get the hang of it.

Thanks, Etta. I’m definitely going to be more careful calibrating my next sensor, to see if that helps. (I’m currently on day 15 of my first sensor and other than the nighttime issues it’s doing pretty well!) Read someone’s comment saying it really needs about 6 hours before it’s accurate…I was just too impatient to get started. :slight_smile:

It occurred to me that you might be missing some calibration opportunities…do you regularly calibrate during times when your blood glucose is stable, and in the range of those extreme highs/lows? I’ve learned it’s really important to give it good information about where you’re at, for the whole spectrum of blood glucose levels you experience.

Thanks…The problem is that I do a lot of snacking :frowning: and correcting, instead of eating 3 big meals and bolusing for them, so there are very few times when I’m completely stable. I’ve been calibrating 2-3 times/day, but it sounds like I should do more.

There also haven’t been many times (especially with the CGM) when my bg is over 140 for any long period of time–I’ve been trying to catch rising bg’s very early–So now I’m considering eating a couple of glucose tabs just to get myself up higher, and stay there for a half hour or so so I can calibrate at a higher number. (I read a tip from someone here that said it’s best to calibrate at 60-something and 160-something, to give the receiver a “slope” for judging bgs. Need to find a way to do that, I guess!)

I wouldn’t push your sugars up higher specifically for calibration. If you’re rarely above 140 then don’t calibrate above 140 because it doesn’t really need to know what a higher number looks like if you aren’t there. The point of this whole thing is to give you better control so don’t through your control off in order to make it work “better”!

Elizabeth, you brought up an interesting question: Does the DexCom 7+ use an one-point or a two-point calibration? I found the following discussion very interesting.

Chapter “1.6.2 Calibration in Vivo” in “In Vivo Glucose Sensing”

Rebecca, I guess my only thought is that I should calculate at a higher value just so it’ll be more accurate at night, when my bg is more likely to get into the upper ranges. I’ve had a couple of instances where I’ve gotten into the 200’s at night, and Dex still read in the 150’s. So I’m thinking it’s just not able to project accurate values for sugars that high because I’ve never calibrated that high…

I don’t know, I may have no idea what I’m talking about :slight_smile:

But that brings up Helmut’s question…Thanks so much for forwarding the link. That section on calibration is interesting, and a little counterintuitive. I was going based on what Rick, another TuDiabetes member who seems to be the resident Dexcom expert, said when giving tips on how to get more accurate readings. He did say that values are calculated via a slope, based on stored calibration values…so a multi-point calibration. (I don’t know his background or where he got the info from, but he did sound like he knew what he was talking about.)

Rick was the one who recommended testing at a lower and higher value, so that Dex could set an accurate slope. If it is determining bg based on multiple points, I’m just worried that minor discrepancies, all within the 70-140 range when I’m calibrating, will set an inaccurate slope and skew the higher and lower values. (If the slope is inaccurate, the center values will be closest, and highest and lowest bg’s furthest. That’s what I assumed was happening.)

It’s worth some experimenting, I guess. I put in a new sensor early this afternoon, and after I let it “stew” for a few hours I’ll be much more careful when I calibrate. I’ll try calibrating for high and low values too, and see how it does…Sunday is my steel-cut oatmeal day, and I’ve never been able to bolus exactly right for it, so I’m sure I’ll have opportunities to see how it does for higher bg’s :slight_smile: I’ll write back once I know.

Thanks so much for all your help and suggestions!