I’ve had a few sensors replaced with no problem because they were way off. They send a new sensor (or 2), not a refund. They don’t want the old sensor back, but sometimes ask that you send them data from your downloads.
Really? Wow. I need to send “broken” sensors back for “inspection” and the data before any discussion about possible sensor replacement… I do wonder why such a difference in the policy.
I found with the trial week the system was off a lot, seeing the same thing now, about 20 points is pretty good assumption( for me at least it is ). That doesn’t bother me too much anymore, I like knowing what direction I am going in so I can take action, especially if I am dropping quickly.
I only enter the BG when it asks for it, during trial I entered more readings and it didn’t seem to make a difference.
First 24 hours is not a good time to judge, mine went up to over 400 but my true reading was only in the 170’s.
wow that is great. it says it shuts off after 7-days, I hope that is wrong. I’m gong to try wearing mine longer than the 7-days and see what happens.
mine just went off, BG low, can’t even read it. Meter says 69, Dexcom says 43. That is a lot. It seems to be like that for me tons of times…
It does shut down after 7 days; it will warn you first. Go to the menu, stop sensor the start sensor. It has no idea you haven’t put in a new one.
My son’s almost always goes up to “high” on the first night he wears it, followed by a couple of hours of ??? and then dead on readings soon afterward. Dexcom said it was possibly because he’s so slim that it takes more time for the sensor to “settle.” I have no idea - I don’t really care since we know it happens and can plan for it. : )
I inserted my first Dexcom sensor yesterday (Sept 1 @ about 7pm) then, today, had a lot of questions with the tech support about problems with the system being off by a significant amount. I believe, now, that I had probably managed to put the sensor into my abdominal muscle; on reflection it felt like an intramuscular injection when I did it and it continued to fell that way.
Nevertheless, I established the accuracy, at least according to Dexcom. Above 80mg/dl the Dexcom and the fingerstick reading must be within 40% of the average (20% error in the Dexcom, 20% in the BG meter), below 80 they should be within 40 (20 mg/dl for the Dexcom, 20 for the meter.) Of course this is an almost useless inaccuracy; it’s the limit. Outside that limit something is broken. In any case both readings should be within 20% (>80mg/dl) or 20mg/dl (<80mg/dl - well, probably <100mg/dl for obvious reasons) of the correct value.
The problem, as other people have suggested, is that both devices are inaccurate. I know my Bayer Contour can be off by approaching 10% because I’ve done multiple readings that differed by about 20%.
What I saw today, however, was not within the acceptable limits. Initially at 6AM I woke up with a low blood sugar and the fingerstick gave me a BG of 59, however the Dexcom said 129. The difference of 70 is well above the permitted 40 and, as soon as I entered the fingerstick reading, the Dexcom went into Sensor Error #1. Later, at 3PM, the Dexcom reading was going rapidly north, reaching 200 at 3:11PM, but the fingerstick said 103 at 3:13PM, a difference of 97 versus the permitted 61. Once again the Dexcom went into Sensor Error #1 as soon as I entered the number. It never recovered (and Dexcom are sending me a new sensor).
Well, my second sensor is now 6 inches higher up my abdomen, where there is more subcutaneous fat. The last lady I spoke to suggested that I should be able to pinch up at least 1/2" of skin+fat (IRC), but at my first site I only had 3/8". I also took care to pinch up more skin before injecting the sensor the second time. With any luck I won’t have the same problems this time round!
The first 24hours is the worst and can have differences like that. Interstitial tissue does not track with faster changes seen on
fingertips.
As for entries from fingertips, I enter throughout day as
i take them. Some folks argue you shoulf only enter the two. I disagree and prefer to add the few extra updates and keep unit
tracking better. Generally , I find better tracking on second day forward and usually within 10 units. That said though, should there be a
fast change you will see differences up to 20 points as unit moves to catch up on the interstitial tissue where sensor is.
I always had bad readings on the recommended gut location and better performance on arm. Why they picked gut as official
position truly escapes me.
It really is a bummer somedays as here you are with your$ 20 dollar hand held with $ 1 dollar strips versus the $900 dollars in latest trick electronics with a $ 75 probe and logic should dictate that the expensive new guy should have gold plated readings. Mounted on your finger tip - possibly but currently nope.
But overall the reading technology upgrade is extremely helpful as one gets familiar with the new technology and its limitations.
and spot checking against finger tip readings and bearing in mind interstitial tissue cannot track fast changes at fingertips.
Once a sensor is settled in after 24 hours, readings do improve but I watch closer with handhed on startup of a new sensor.
The 20% plus 20% argument is BS
The accuracy is +or- 20%
The idea that the difference you see on the dex is due to the difference between ISTF and BG is also BS - the algorithm can be made to accommodate the differences. The navigator surely did.
Ive been wearing the Dex on and off for almost 2 years. The ONLY thing its good for is trends… Is my BG going up or down ? has the rise peaked and started down yet ? The numbers are OFTEN off by 100% and at least 40% of the time off by 50%. I should call Dex support every time BUT I cant spend an hour or more per crappy sensor downloading data and uploading it and explaining it to the support people. Eventually Ill tire of paying 20% for the sensors. and simply stop ordering them.
The really sad thing is that Dexcom claims they have better accuracy than Medtronic. If Dex is the best then the artificial pancreas project is doomed.
ANother happy customer - oh great. As i said, the industry should be shot over the 20 % BS.
Tracking though is not presently good as reported to fast moving events.
I have made it work for me but that does not mean I am happy either with issues like those raised raised by prior writer.
In addition, Dexcom prone to hide out and not respond which is unfortunate.
In your opinion after reading one post Im a lunatic ? And full of poop ?
Great argument - clearly a member of the debate team … Thanks for sharing.
Back on topic - call it whatever you want - algorithm - accuracy - product quality - computer program - how ever you describe it - Dexcom is doing it BADLY by ANY measure, but especially badly when compared to the recently departed former competitor the Navigator…
I used a navigator for 2 or 3 years and it was typically within 10 - 15 points of my finger sticks. it was the exception when it wasn’t.
More of my lunacy is the question, if there is NO math ( or algorithm) going on between your calibrations, the ITSF and the readings then why, when the Dex says your BG is 200 and you test and its 95 and you calibrate the 95, does the Dex drop about 15 points to 185 and SLOWLY trend down ? That to me is an algorithm. But you will call it something else…
Doug in Skagit County - All ANY of us can provide are opinions and experiences, which is the point of these kinds of social networking. The FACTS are that twice today the Dex was off by over 100 points.
My opinion is that SUCKS.
.
Doug in Skagit County-
National Institutes of Health is also apparently full of poop
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2825632/
“Thus calibration algorithms capable of reducing CGM error are important additions to the arsenal of data processing techniques that help transfer raw current into BG readings. Algorithms reducing the time lag are critically important as well.”
The Journal of Diabetes Science and Technology also seems to think there is an algorithm to correct between the sensor and the finger sticks …
http://www.journalofdst.org/March2010/Abstracts/VOL-4-2-ORG16-BEQUETTE-ABSTRACT.pdf
“Algorithms for real-time use in continuous glucose monitors are reviewed, including calibration, filtering of noisy signals, glucose predictions for hypoglycemic and hyperglycemic alarms, compensation for capillary blood glucose to sensor time lags, and fault detection for sensor degradation and dropouts. A tutorial on Kalman filtering for real-time estimation, prediction, and lag compensation is presented and demonstrated via simulation examples. A limited number of fault detection methods for signal degradation and dropout have been published, making that an important area for future work.”
“The 20% plus 20% argument is BS”
Hum. Is that the statement of someone well versed in statistics? In which case why don’t you give the correct answer? Or is it, itself, BS? Ok:
We have two BG meters. Both are presenting us with approximations to our actual, intra-veinous, blood glucose. The FDA requires these meters to be within 20% of the correct (IV) answer some proportion (probably 66%) of the time. So:
reading x = IVBG +/- 20%
reading y = IVBG +/- 20%
Therefore (and, yes, I know this is wrong):
reading (x-y) = (IVBG +/- 20%) - (IVBG +/- 20%) = +/- 40% (of IVBG) 66% of the time.
Ok, that’s wrong because (a) the answer is 37% and (b) that assumes that the two meters are acting independently: let’s hope they aren’t!
I have to admit I interpreted the comment as a complaint about the accuracy of the Dexcom compared to the Abbott FreeStyle Navigator, probably when compared against Abbott FreeStyle test strips. Abbott claims, here:
That 81.7% of the readings were in zone A ("clinically accurate, would lead to correct treatment decisions) and 16.7% of the readings in zone B (“would lead to benign decisions or no treatment”) using the “Clark Error Grid”, with a total of 98.4% in either. Dexcom claims (in chapter 10 of the Seven Plus CGM System User’s Guide) that 73% of the Dexcom readings were in zone A and 23% in zone B, giving a total of 96% in either.
The Abbott results dropped to 96.4% when they conducted the tests at home, not in the lab. The Dexcom tests were conducted for seven days with one of them in the lab.
We can see the accuracy figures as well as the statistical significance from the Dexcom book, I guess the Abbott data is available somewhere too but it wasn’t immediately obvious to me where. Dexcom has 76% of the readings within 20% (of IVBG), 90% within 30% and 95% within 40%.
As Dexcom observes it is more informative to overlay accurate blood glucose readings (not from a finger stick) over the Dexcom trend.
The FDA rules are a different potentially interesting argument… The point Im making is that its possible to make a more accurate, precise sensor and Dexcom isnt doing it. The fact that they are operating withing the FDA rules just means the FDA has set very low standards. If there was a more accurate option I would be using it.
In order to discuss an algorithm Im required to provide one ? Huh ?
I never said it would be easy for me - Simply that it HAS been done. And that Dexcom should strive to improve theirs.
I thought that this discussion is used by users and POTENTIAL users and they should see opinions from BOTH sides of the discussion.
I guess this discussion is for Dexcom cheerleaders only.
Rah Rah - Dexcom you are doing a great job - keep it up. Dont worry about accuracy. We love you anyway…
Sorry I participated…
The rules are asinine especially when one is chasing lows. These rules are unacceptable and FDA should know better. On the high side, yes the errors do not have much impact. On low side totally different story.
I am fed up with statistical analysis that attempts to prove some stupid point and not real world.
There are two approaches in this world. Back in early days of Boeing Engineering, they would literally
bend and stress an airplane to see actual wearout - stress factors to prove they had made/met worst case design goals and safety. . There is another pack of clot morons
who do statiatiscal analysis to show why statistical analysis is adequate and why doing actual worst case testing and design are not necessary as statistictal analysis says plane design should be ok.
Which plane do you want to trust your life to?
Doug:
Excellent response.
In fact I do get very useable helpful data not withstanding all the worts.
Yes statistical analysis provides a starting point to see if any co-relation and then hard testing needed to validate that the statistical analysis was picking up correct issue.
I do not need spot on readings and I do work with trends and handheld cross checking each other.
Its just the balance of the human interface at Dexcom and the issues like having to keep my unit chilled so it does not jam and stop, watching out for interfereing servers/and wireless gear crap
causing machine to jam up on old reading ( worst in my condo /home) , the startup delay which really can be a whole day and trying to get max use out of sensor.
I am not unhappy but the dancing and waltzing getting it to run 24/7 without major hickups can be fun.
Yes, this is good step forward. But as a 40 year experienced electronics engineer and computer hardware engineer, I see the warts and wrinkles up front while Dexcom offers little explanation/detail; upgrades ( FDA won’t let us fix nothing - what you get is it)
If I had a emulator and development system, I would dive in there to see what they actually did both in great works, difficult tradefoffs and how good the manufacturing/testing worst case work was done.
I just wish the interface knowledge sharing, customer interface guidance was better at Dexcom. If the FDA is buggering that up - a pox on both their houses.
The fact one cannot upgrade software issues on a product to make it work correctly to match original approved design spec and not adding new features without massive federal approval checking process is outright shortsighted and unhelpful. Yes regression testing needed always - but surely the FDA can offer process, approval,reporting that promotes fixing the bugs, eases user problems and makes experience better without ham fisted regulation effort locking product to ocean bottom with 10 ton anchors.
As one who has spent thousands on finger stick technology strips - 32 readings a day until I got Dexcom, As great as it helps ; it just seems such a contradiction to be using a $ 900 electronics/computer package with $ 300 odd dollars in sensors per month ( and less if sensor grants one extra use) and using a $ 20 dollar handheld and $ 1 dollar strips to calibrate, keep cgms in line and then get occasional off the wall readings and outside the 20% .
On top of that , ones cost are really the handheld unit 6 to 10 strips a day plus the CGMS and probes. Is that bad - no, it is saving my life and getting my liver and type 2 monster caged after 30 years of being driven wrong.
On top of it, every time there is a crisis blowup and thanks to low speed tracking , I am out with the strips seeing what is tearing loose.
The CGMS really catches a lot of data having to do with digestion times and other idiotic behaviour in my body that finger stick machines cannot do.
Thank you for adding to discussion and excellent thoughts.
OK, Lessee...
I've been on the DexCom (7 Plus) since 2009, May. Long enough that pretty much all of the varying-experience scenarios reported here are inside my experience.
Doug, the only really important question I'd ask is, "Are you happier and better off managing the diabetes with the DexCom than you were without it?" If yes (...which is, by the way, my answer...), then even with its clear and (experience-obvious as opposed to not-quite-to-promises-)obvious shortcomings, it is well worth its expense and its incumbent frustrations. If not, then you're under no obligation to continue using it--ultimately (and I'm certain you know this, but it bears repeating...), you get to choose how you manage the disease.
For me, the DexCom has been a major godsend. I've seen the wide swings from finger-stick readings, but having the continuous data stream, and especially being able to see the trends is what I'm talking about. My A1c's are improved, and the incidence of BG crashes, while not zero (...although, it was zero for the first 18 months I used the CGM...) is way down from the three or four call-the-parameds incidents a year I was having before the CGM
Now where algorithms and such are concerned, somebody in the thread mentioned Kalman filtering. I have no direct view inside DexCom's engineering, but I know damn well they have to use some form of predictive number-crunching (which is precisely what Kalman filtering is an example of), since it's well known and understood that interstitial glucose levels lag (by 5 minutes...10 minutes...?) BG levels. There are also variables like where the sensor wire is inserted and whether or not that particular tissue is vascularized per DexCom design specs. (I have lipomas on my abdomen, and when I inadvertently stick a sensor into one of them, I usually have to toss it and start again within 24 hours--the infamous "???"s, doncha know...!)
Now in this context, I think the comments about the FDA are spot on. What they are really saying, without saying it (or, for that matter, permitting DexCom or anybody else to say it) is, "We don't trust you adolescent, pus-brained idiot, bone-headed members-of the-unwashed-masses, who have never been attorned into the brotherhood of Medical Validity Evaluators, to make any kind of judgment regarding your use of all these wide and varied things that you can only have access to if we say you can (...we, of course, being the only people on the face of the planet qualified to make such judgments on your, or anyone else's behalves...). So just shut up and trust us--that's what we're here for!" Frankly, I’d love to be able to write an app for my smart phone that acted as the DexCom receiver--one less gizmo to hang on my belt! But having no access to the design specs, or any of the engineering, or even what proprietary variation (if it's as I suspect) of BlueTooth protocol they're using, and since DexCom can't offer an Android app without getting massive FDA approval, any discussion of improving things on my own, or in the company of like-minded enthusiasts, is moot. Open source will never to happen with anything the FDA has hegemony over.
A sinecured bureaucrat, regardless his bona fides, is not, never has been, and never will be, a substitute for the synergy of an educated, informed, and motivated client ("patient ") working with a competent, informed, and interested professional consultant ("doctor" (...which, by the way, comes from the latin for "teacher"...)). All of the long, sordid history of bureaucratic interference under the aegis of "protecting the public" has not, in any demonstrable way I can see, ever managed to add to the "public welfare" (all the trumpet-voluntary protestations to the contrary notwithstanding), and in many demonstrable instances, has subtracted form it egregiously.
So maybe it's time to start a new thread about the efficacy and validity of government-managed health care--this thread being about DexCom accuracy, and all. Speaking once again from my own personal experience, I do find that the DexCom's accuracy, especially in the low ranges, is more than adequate to make my worries about BG crashes way less than they used to be, and to provide, overall, a significant improvement in my ability to manage the disease. I'm sticking with what works for me!