I recently started a Dexcom 7 Plus CGM about 4 days ago and have mixed opinions. My first sensor failed (Dexcom replaced sensor) and my second sensor has been acting erroneously (Dexcom has just agreed to replace this one too). I have left the second one in to see if it improves OR to see if what I’m expecting is normal.
THe first day of the second sensor was AWESOME. Very accurate results, usually only 5-10 points off. Very, very good. However, one morning I woke up with the ??? reading and eventually it went away after a few hours. When the readings came back the accuracy was notably worse, usually varying at least 30 points, sometimes as much as 80-100 points off. I have tried to calibrate more frequently but I'm not sure if that is supposed to help. When I re-calibrate it will recognize the reading and then the reading on the Dexcom will match closely to what I entered in, but then in 2 hours or so it will be off again by several points. Is this to be expected? This sensor was placed in on Tuesday evening, so at this time it has been in for only 3.5 days.
Here are examples of my recent readings:
Dexcom 133 Meter 234
Dexcom 181 Meter 229
Dexcom 88 Meter 141
Dexcom 69 Meter 79 (I'm ok with this one. 10 points off is acceptable to me).
So, this is my situation, and since I am very new to this equipment I have come to the experts to help me out! Is this expected? Is this a bad sensor? The Dexcom Tech Support said it was likely a bad sensor, so they replaced it, but sometimes it works and sometimes it doesn't. How close should readings be after 3.5 days in insertion?
I find that the accuracy you are experiencing is about normal for me for the first seven days of a new sensor, then, as if by magic, in the second week (not reccomended, of course!) the accuracy gets MUCH BETTER. I really dont know the science behind this, but it seems to be the “norm” among the majority of dex users in this group. Patience is key…roxylove, Patience! I hope you will find a solution and PEACE! PS, I use the dex as an indicator of where my bg is GOING, and not as a repleacement to finger pricks. When you look at it in this light, it becomes invaluable.
Readings can be up to + or - 20% of a BG readings…(which can be up to 20% off themselves)…
This wide range of inaccuracy is common to ALL CGMs…
Try this…
Insert a sensor and dont start it for 12 hours. (seriously)… If you sleep with it, you want to wait a bit after waking up to try starting it… ISF fluid doesnt circulate as well as night…(so you might wait an extra hour if you havent been up in time to start it) (this sometimes causes false readings/alarms at night… )…
Remember theres a 2 hour startup…try starting the sensor now (after its settled in for 12 hours) and see if you get better readings… Sometimes (people have found). that after insertion, sometimes it takes some time for the sensor to settle out… Usually the first day is the worst… but even when they are mediocre, usually the high and low alarms still work and are on target… Theres also a lag time of roughly 15 minutes… If your BG is relatively steady, it will be more accurate… You want to recalibrate when your reading is closer to being in range and not while its trending up or down rapidly… Exercise can also throw off the sensor because you drop faster than the sensor can catch it… sometimes might even go into ??? mode after an exercise session but usually comes up relatively fast compared to some sensor errors…
You do sound like you had an off sensor… Its odd but some sensors behave nicer than others, and some are just consistantly off… This is true of all CGMS that its trends not individual readings… But for some people, certain devices seem more accurate for their body…
Also do you wash your hands before calibration with soap and water NOT alcohol or hand sanitizer… this can give an off BG meter reading (which usually doesnt turn out to be a big deal), but even the minor error from that can be amplified … Technically you can calibrate anytime but the best times is when your BG meter says its in the target range or close to it… (ie not like really high or low)
Good luck. and dont panic … youll get a feel for it… it really is cutting edge technology and has some of the quirks relating to it
I think there are a couple of things that really trip people up when it comes to figuring out how accurate their Dexcom is.
Jake hit on one of the most important considerations. There is ALWAYS a period of lag between what your BG actually is and what your Dexcom is reading. So, you will NEVER have instantaneous agreement between what your meter reads and what your Dexcom reads, even if both are 100% accurate.
Even when your BG is stable, your meter may read 95 and your Dexcom may read 95, but your meter is telling you what your BG is now while your Dexcom is telling you what it was 15 minutes ago. When your BG is fluctuating all over the place, it’s like watching a dog chase its own tail.
So, what happens is people may see a big difference between what their meter says and what their Dexcom says so they immediately want to recalibrate to get their meter and Dexcom to read the same thing all the time. All that does is confuse your Dexcom even more and lead to even more inaccurate readings.
The situation just gets worse when your BGs are trending in one direction. It will ALWAYS take your Dexcom awhile to catch up with the BG, so when you see and arrow indicating a trend, that change has already been happening for 15 minutes. It’s more about using your Dexcom to anticipate where your BG is rather than trying to let it tell you what your BG is NOW.
Throw in the fact that both your Dexcom and your BG meter can have errors up to 20% of what your BG actually is and you can see that using your Dexcom becomes more art than science, really.
Roxylove,
I have had my Dex 7+ for 11 months. Congratulations on picking what I believe is the best CGM on the market after I spent 3 months trying to pick one and tried Dex and Medtronic.
I agree with the others about the +/- 20%.
The hand cleaning is VERY IMPORTANT - no foreign substances on your hands.
Do a BG every time you dose insulin and enter the BG in the Dex. It actually improves the accuracy, contrary to some people - read the Dexcom patent and technical material that came with your Dex. It is almost as good as Ambien <<GRIN>>.
Let me number your patterns above 1= 133/234, 2=181/229 3=88/141 and 4=69/79. #1 is way off, repeat the stick in this case. I have seen some times a stick will be 450 one minute and as fast as you can reload and restick with the same meter and stick batch the stick will be 148. So, #1 - repeat the stick if this happens and call tech support for the meter. #2 Add 36 to 181 (20%) and you get 217 then subtract 46 from 229 and you get 183 – This one is at the +/- 20% ALMOST. # 3 is about 90 + 17 (fudge factor) = 107 while about 140 - 28 = 112 – close. I would recheck again in 30 minutes to an hour and make sure the arrow on the Dex is in the level position. #4 You said for yourself - it is OK.
Bottom line - Dexcom is a tool like a hammer and nails are to a carpenter. You must practice with the hammer and nails, learn the different types of wood you are nailing, and learn the angles nails need to be inserted to be a skilled carpenter. Now, you are using a Dex and it will take time, temperament, and talent (all translates to patience and asking for help) to become the master with this tool.
there are days my frustration level is through the roof because of either crazy readings, carb miscounts, Glycemic Index of food (I think it is slow into the blood and Dex says it is all in my blood yesterday and the graph goes straight up).
There is also somewhere in the dex literature that you dont want to calibrate it more than 4 times a day (unless the unit prompts you to)… occasionally when it gets really out of whack, theres a thing where Dex support has you calibrate it every 15 minutes for at least 3 calibrations in a row… If im in range when i check my BG and the dex is stable, i usually will enter it as a calibration. if im peaking due to after a meal… ill wait till it comes down a bit before i retest and calibrate…
Thanks for the great advice. Despite the readings I listed earlier, I do think I jumped the gun a little bit. It has been near outstanding today, especially this evening. We were at a wedding (a bunch of different food, drinks, dancing, not much time to check BG) and the Dexcom was spot on. I checked before we went in (Dex = 114, Meter = 124), and was unable to check when we returned to our car 8 hours (Dex = 104 Meter = 109). I monitored my screen throughout much of the night to monitor the sugar level and watch the trends after dinner. I have a pretty good sense of how my body feels at certain sugar levels, and I felt great the whole evening. The Dexcom and Meter readings before and after the night reconfirm that it worked exactly as I need it to!
I agree with what everyone has said about it showing trends, not instant glucose data. I was just very concerned with the way-off numbers I posted earlier, particularly where it showed 100 points off. I am willing to write that off to a fluke error somehow, either on my end or the Dexcom’s. Most of the readings were way off yesterday afternoon when I got ahold of tech support, so maybe the sensor has just “settled in” more as well.
I have used only my abdomen for sites as I have only used two, however I am interested in other site locations. Has anyone had success with other site locations, such as a thigh or arm?
Also, can I calibrate too much? For example, when I test and the Dexcom and my Meter are off, should I re-enter my BG into the Dexcom every time? Generally, for the most part, I have been entering in every BG number that is off by 20-30 points or greater to bring the Dexcom more into the range that I am in. However, I don’t want to confuse the device, but I have no idea the proper way to do this.
I agree, the second week seems to be more accurate. Mine has been as much as 65 pts off but most of the time quite good. I just use it as a guide, if it is going up or down. If it’s reading high or low and buzzing at me I usually don’t worry too much and will test to see what it actually is before reacting. I’ve also wondered if entering BG reading more often helps or hurts.
I had another off reading, or what I consider to be an off reading, this morning. Dexcom says 133, Meter says 78. I’m upset for two reasons - that is too far of a gap to be off AND I’m pretty close to having a insulin reaction at 78. Another five minutes and I’d be in trouble, while the Dexcom would still be thinking I was over 100. Ughhh.
I would definitely say, from my experience, not to recalibrate just because you feel the Dexcom is way off.
I’ve really had to show a lot of restraint regarding this issue myself but it has really paid off. I’ve had my Dex be as much as 30-50 points off at times, but if I let it go, it eventually comes right back into range. I’ve tracked my BG on these occasions and, clearly, it turns out the Dexcom is just lagging behind the changes in my BG. Once the BG stabilizes, the Dex is able to catch up and give comparable readings again.
I have calibrated up to 4 times a day, but only when my BG is stable and only when it’s off from my meter readings by a lot more than 20%. There have been times when the Dex has called for a calibration after 12 hours and I’ll just reenter the number that the Dex is showing me. I feel like I can do that because the BG is stable and a fairly recent test has shown that the meter and Dex are within 10% of each other. No sense in wasting a test strip just to correct a difference of 10 points.
Last week, I put a sensor on the outside of my upper thigh, about 5 inches below my hip and right down the midline. It’s been, by far, the most stable and accurate sensor I’ve had in 2 months of wearing a Dex. The spot is a lot more convenient than my abs and the adhesive strip hasn’t even begun to start peeling yet because it doesn’t get bent and twisted like it does on my abs. The only problem was A LOT of bleeding, that restarted 30 minutes after I put the thing in because I went for a run. Once the bleeding stopped, i gave it 12 hours before starting it and it’s been running like a champ since!
Good advice! I’ve heard the Dexcom sensors die quickly from “blood poisioning.” I take it that this did not happen with you? They say it needs to be in a “fatty” area, I guess part of this reason is to avoid so much blood. Have you tried any other locations?
Thanks!
Also, my site is starting to come off. I did not use Skin Tac to put it on, but I have some now. Could I put some underneath the flaps that are coming up? Or should I just use adhesive tape?
I use 4 sites on my abs that I rotated through my first month. They gave me varying degrees of accuracy and problems. I can pinch some fat in those areas.
My thighs are probably one of the most lean areas on my body. I was hesitant to try my thighs because I wasn’t sure how the Dex would handle it, but I didn’t feel that the areas on my abs had sufficent time to heal before getting jabbed with a Dexcom sensor again. I just felt I need more areas to rotate through. Other than the bleeding when I inserted the sensor, it really has been the most problem free and accurate areas by far, so I guess the bleeding, in my case, wasn’t an issue for the sensor.
I use Opsite Flexifit when th adhesive starts to go. That works well enough for me. I tried Matisol but it was messy and didn’t work as well as I hoped. There are a few threads both in this forum and the Omnipod forum discussing ways people deal with the adhesive strips.
ugh…another bad experience. I woke in the middle of the night (actually 11:30pm) with the typical “low” feelings. Dexcom says 76… Meter says 30. This is over 20% by a considerable margin and I find this to be just unacceptable. I know the readings are behind because it does not actually test the blood, but this is considerable and dangerous.
I’m not quite sure what to do or where to go from here…
Roxy - What levels do you have the “alarms” to go off at? I had to set my low for 80, and my high for 200. Sounds like you may have to do the same…unless the meter starts reading closer in the second week. (which, as I pointed out earlier, most wearers say it does, and it did for me.) (I would just change the alarm levels on week 2). I know this is frustrating, but dont let it steer you away from what is pretty good technology! Good luck and PEACE.
Hi Roxy. I had a dexcom user tell me that when the dexcom number is way off track, I should enter three fingerstick numbers, fifteen minutes apart. this will supposedly put dexcom back on track a lot better than using only one fingerstick entry. I have not tried this yet, but I am going to the next time I get a wild dexcom number.
