My sugars today have consistently been running 30-40+ points LOWER on Xdrip+ vs finger stick. I tried calibrating but it isn’t helping. Unsure if I should change the sensor, transmitter or both.
Transmitter days: 96
Volt a: 300
Volt B: 272
Resistance: 1773
Temp: 36 degrees C
Sensor is 10 days 21 hours old.
Mine is similar, except Resistance = 1035.
My trans days is 64.
You might find more help here. I think same would apply to G6, if you want to reset days on transmitter.
I’m almost at 90 on my G6 transmitter… I think I will start a new thread to track it to see how long it will go…
@bpollina It’s the sensor. Same thing happened to me three times with the G6.
Switch sensors and you’ll regain pinpoint accuracy.
@Mikeb you might check first, I think there are several threads already about transmitter life and duration.
@bpollina Oh, I forgot. Your voltages and resistance are looking pretty good. My brand new transmitter looked almost like that on day 1, and I’m now on day 93.
My experience is that the sensor is the thing that will fail. As a person who has programmed computers for all but six years of my diabetic life the transmitter itself cannot cause errors in the readings that would be fixed by a new transmitter.
My readings (I have stopped calibrating) are always lower than a fingerstick over 200 and tend to be higher (this may just be the 10 minute delay) below 100.
Bear in mind that there is a 10 minute delay and, indeed xDrip+ shows this; fingersticks are (apparently in Jamorhan’s opinion and also in mine) about 2 (1.5?) readings ahead of the G6. My numbers, for reference, not that I have the faintest idea what they mean:
Transmitter days: 100
Volage A: 299 (mV ?)
Voltage B: 273 (it’s been ‘red’ for days, don’t know what that means either.)
Resitance: 1631 (ohms? Also red)
Temperature: 38 (degrees Centigrade? I suspect he means Celsius, no one uses Centigrade, but there are no degrees in Celsius.)
Sensor days: 7.4
I just happened to fingerstick because the G6 said I was at 270; 201. No surprise to me, I had just enjoyed a hot bath with my wife. That was at 7:40PM, now, at 8:16PM the G6 says 179 down 3/5min and the fingerstick (solely for this post) says 162, so that’s a difference of 11 (179 - 2x3 vs 162). I don’t expect them to even vaguely line up outside the 100-150 range.
I should add that sometime in the last 8 months someone (@Chris?) said “don’t calibrate”. I was, of course, sceptical, so I did continue to try calibrating. I was proved wrong, which is one of the greatest joys I can ever experience [seriously], and am now a more knowledgeable, though perhaps not better, person. I don’t calibrate; when the sensor starts to whack out (about 15 days in my experience) I change it. Putting in a new sensor wipes out all those calibrations, but then I think so does putting in a new sensor.
John Bowler
Unless I am mistaken, the oxidase on the sensor wire gradually diminishes which causes noisy sensors and. Sensor errors.
That is my working hypothesis.
Dexcom over the last year or two has mentioned several times that they had tried a new oxidase/oxidase vendor on the G6 and that was the reason for underperformance. They had similar issues on the G5 about 5 months later. Since then, they have either returned to the old oxidase/oxidase vendor or improved on the current one as they no longer discuss this subject in earnings calls. Dexcom also tried out a new adhesive vendor which is why the early G6s kept falling off.
If you wish to read the earnings calls, I suggest starting with the Dexcom 2018 Q3 call at Seeking Alpha. In that call they discuss both the adhesive and the oxidase.
What transmitter information are you looking for?
I don’t understand your reasoning for this statement. Sure the digital data transmission will be uncorrupted, and the digital calculations in the processor and memory are unlikely to be glitched, but I don’t see why the analog sensing circuits couldn’t age into inaccuracy.
I’ve heard that reasonable-sounding explanation many times; it just seems to make so much sense that somehow the sensing chemicals “get used up.” Unfortunately, it is an “alternate fact.” I wish there were some way to stop its spread in favor of the actual scientific knowledge on the topic. The catalyst doesn’t get used up, it merely facilitates a chemical reaction.
Research that I found on the topic of CGM sensor degradation (when looking nearly a decade ago) principally attributes it to bio-fouling and encapsulation processes associated with the tissue’s foreign-body response (like when you get a splinter). A key job of the highly-proprietary coatings the manufacturers apply to the sensor wire is to try to make the sensor “invisible” to the body so as not to provoke the foreign-body response. (The coatings also throttle the glucose and oxygen transport to control the catalytic reaction to a rate that is good for measurement.)
Anyway, it’s not my field of expertise so I’m pleased to be corrected if I have misread the literature or if the papers I read are bad, but here are some references that I came across all those years ago.
“Estimating Plasma Glucose from Interstitial Glucose: The Issue of Calibration Algorithms in commercial Continuous Glucose Monitoring Devices”
http://www.mdpi.com/1424-8220/10/12/10936/pdf
The first few pages give an overview of the technology in 2010 and describe the chemistry that makes it work, and on page 10941 it describes the causes of sensor degradation as inflammation, encapsulation, bio-fouling.
“A Subcutaneous Glucose Sensor With Improved Longevity, Dynamic Range, and Stability of Calibration”
http://care.diabetesjournals.org/content/23/2/208.full.pdf
On page 209 it describes one system of protective sensor coatings for an implantable sensor. On page 213 it states “an enzyme electrode sensor involves … no consumable reagents”
“Amperometric Glucose Sensors: Sources of Error and Potential Benefit of Redundancy” Amperometric Glucose Sensors: Sources of Error and Potential Benefit of Redundancy - PMC
They describe how the technology works, and note things like pressure lows, the trauma lows during the hours after sensor insertion, and the phenomenon of bio-fouling reducing sensor output over time.
“A Review of the Foreign-body Response to Subcutaneously-implanted Devices: The Role of Macrophages and Cytokines in Biofouling and Fibrosis”
Biocompatibility of Implanted Diabetes Devices: Part 1: A Review of the Foreign-body Response to Subcutaneously-implanted Devices: The Role of Macrophages and Cytokines in Biofouling and Fibrosis - PMC
This article goes into depth on the topic of bio-fouling, causes and techniques for mitigation.
Here are 3 more references that also touch on sensing and sensor degradation if you’re really interested; I haven’t checked these links to see if they are still live.
“Estimating Plasma Glucose from Interstitial Glucose: The Issue of Calibration Algorithms in Commercial Continuous Glucose Monitoring Devices”
Estimating Plasma Glucose from Interstitial Glucose: The Issue of Calibration Algorithms in Commercial Continuous Glucose Monitoring Devices - PMC
“Electrochemical Glucose Sensors and Their Applications in Diabetes Management”
http://pubs.acs.org/doi/full/10.1021/cr068069y
“Glucose sensors: a review of current and emerging technology”
http://onlinelibrary.wiley.com/doi/10.1111/j.1464-5491.2008.02642.x/full
So, you have entered into an area that I am in fact pretty knowledgeable. And while @elver’s explanation is simplistic it is in fact true and part of the issue, as are the additional issues you have brought into the conversation. It would be a gross simplification to call Glucose Oxidase (GOx) a sensing chemical. It is an extremely complicated enzyme that contains FADH2 centers which will selectively oxidise glucose in a sample. It is the amazing ability of an enzyme to perform a function that is the basis for most of the glucose sensors on the market. Enzyme’s are great at their jobs, but are somewhat fragile especially at elevated temperatures such as those found in the body. Here is a paper aimed at showing the robustness of GOx attached to a silicone surface and stored for 3 months:
(Full paper if you want to read: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3705523/)
As you can see the enzyme activity is being reduced by storage. This isn’t a big problem because GOx is cheap enough that you can always add enough to overcome this in most sensor system.
Once you put it in the body, in addition to the elevated temperature, there are a number of issues which you mention that the manufacturer’s have to deal with and try to minimize. It is quite a difficult challenge, and I am really excited by how well Dexcom and Abbott have worked to solve the problems and issues that arise.
In summary, there are many factors that affect sensors and you guys have been having a discussion about some of there. Trust me, there are more.
@bkh, perhaps “dimished or used up” is too simplistic a way of expressing the ability of the oxidase to facilitate a chemical reaction in the interstitial fluid, much like a depleted lead acid battery. On the other hand most people without an engineering degree easily understand the original description.
