What’s the logic of not calibrating more often? When the sensor is spot-on, isn’t it helpful to provide it with positive reinforcement, as it were?
The Dexcom gets an electrical reading from the wire and needs to show us a result in units we can understand. If the ratio between the electrical reading and actually blood sugar is changing (as it may as sensors get older) than a calibration is helpful. I've never found these changes to be fast, so I generally don't care to change this ratio until I need to.
Some feel that frequent calibration will mean more accurate results, but in reality I think a lot of frustrated Dexcom users that post here are calibrating when they aren't level, and get flustered when the results diverge from their meter later in the day.
For me, calibrations are something that I do very infrequently. I usually go days between calibrations. I'm still checking my blood sugar with a meter, but unless the results aren't close, I've found that entering more data than is required only leads to variable accuracy.
Also, if the Dexcom reads 100, and you enter a calibration of 100, it will likely tell you that you are now 90. Something in their software seems to think this is best, but I see no need to add extra jumps that aren't necessary.
Niccolo - It'd be nice to see a comment from someone that understands the inner workings of the actual Dex algorithm as well as a good understanding of statistical measures. An ability to explain in plain English would also be a plus!
As an everyday observer I can note how good the correlation is between my fingersticks and the Dex. That's the best I can do.
I can easily understand that calibrating when BGs are changing quickly is a bad idea. The inherent lag between blood BGs and interstital BG proxies explains that.
Since the system is designed for two calibrations per day, it implies that doing a lot more than that is not optimal. I feel ill-equipped to argue in one camp or another.
I just started the Dexcom last week. When I got set up by my CDE she said that three times a day is the "sweet spot" and I received a call from what seemed to me like a knowledgeable lady fro Dexcom. She said that twice a day was sufficient and anything more was unnecessary. My CDE did say to always calibrate before going to bed. Terry..I know it's not static but my receiver rebooted itself because I was welding at work.
This may very well be another example of less is more!
I think so...that's the way I'm going to try it. Besides, it's easier with less needle pricks :)
It'd be nice to see a comment from someone that understands the inner workings of the actual Dex algorithm ...
That's an interesting thought. But also very unlikely to ever happen in any way other than someone speculating. Dexcom is intentionally very secretive about their technology.
Below is a link to an an older (May 2014) article in Diabetes Forecast about CGM sensor technology. In addition to some hand waving the author also talks about her visit/tour of a Medtronic sensor manufacturing site.
Anatomy of a CGM Sensor by Erika Gebel Berg, PhD
Wait! Why on earth would I post an article that is primarily about Medtronic CGM in a Dexcom discussion???
That's the point. She also asked to tour Dexcom. Dexcom refused. They definitely want to keep whatever "special sauce" tech they have to themselves.
-iJohn
Interesting link. Thanks for the comment.
But Dexcom instructs us to enter all fingerstick data, right? Two calibrations/day is just the bare minimum the system needs. That’s what I’ve always been told, this forum is the first place I’ve heard the notion of avoiding excessive calibration. And calibrating occasional highs seems important, too, otherwise the system doesn’t know what they look like, right?
But all of that could be empirically moot. As you say, wish we had actual info!
How do you go days without calibrating? What about the 12 hour interval calibrations when the Dexcom asks for a calibration?
I just ignore it. They aren't required for it to work.
Agreed, I find it bizarre when the Dexcom uses calibrations to adjust itself away from the calibrated reading.
My first dexcom G5 receiver failed two weeks ago - after getting a warranty replacement I had this message on the seconds day.
Since it keeps doing it - and today all the data appeared to have disappeared. On a shutdown/restart it did reappear, but I think it is a manufacturing issue. The new device came out of packet and failed within 3 hours.
In the subject of calibration - if you supply repeated calibration data it can be very accurate. I use the old freestyle lite blood sticks and after 8 days get results within 0.1 mMol/L - within 5% (Yes I’m in Europe).
I am onto my 3rd receiver due to the system check passed. Once again I am getting the same message. When I spoke to dexcom about it, they reckon that they don’t get this message very often and it was unlucky that I keep getting it. I have had my 3rd receiver for 2 days now and I am getting it again. WTH.
I have had the System Check Passed message a lot recently after years without an such thing occuring. Dexcom has replaced the Monitor 1 or 2 times and now is sending a new case. They have offered the static explaination but that does not seem to fit since the house is not that dry. I suspect that there is either a hardware or software issue but Dexcom cannot figure out the specific cause. The only probelm is that there is missing data for a period time prior to the System Check message.