That’s important! I find my Dexcom to be LEAST accurate first thing in the morning, after a night of sleep has allowed me to dehydrate a little. I find that drinking a glass of water at least 10 minutes before doing a ‘fasting test’ results in much closer Dexcom-meter results. When I don’t do that, It’ll be off by 20-30 points, and, if I calibrate based on that, it will be off ALL DAY, as well.
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Interesting. I probably ignore or go directly against most of your bullet points and still get great accuracy. My CGM vibes must be spectacular. I even used to get useful and fairly accurage data from the old-style Medtronic Sof -Sensors (AKA elephant harpoons).
When starting a new sensor (or restarting an old one), I always do the calibrations one straight after the other (often from the same drop of blood). It seems like the first reading showing on the screen will usually be 0.2 mmol/L lower than the lower of the two readings.
I routinely calibrate if my BG is below 4.4 (80) and less often if it is above 11 (200). With the Vibe, if a calibration is overdue, the one-press Dexcom screen just shows the message “Calibrate BG” and you have to faff about with several button presses to get a reading. I find this irritating, especially at nigh, so will calibrate at bedtime to avoid having to wait for BG to come into range.
With the Vibe, after giving a bolus the pump will alarm and ask if you want to use the BG reading for a calibration - I usually press the OK button, which means I typically calibrate 4 or more times per day.
I have calibrated when the trend arrow is diagonally up or down (although I do try to avoid this). The algorithm seems to be able to deal with this and anticipate the sensor lag.
Maybe I am just lucky…
Joel
@jjm335 , I hope you won’t take my disagreement below with the points you are making negatively!
From an experimental point of view this seems suboptimal to me. The reason for the 2 samples, I am guessing, is that the measurement from a meter-strip system is very noisy (i.e. inaccurate), by often 15% or more: the multiple measurements allow you to take out some of that noise. So making sure to get 2 different drops of blood, possibly from different hands, at a slightly different time even, makes more sense to me. Since a strip/meter measurement can be very far off, it makes sense that you would like to dial out some of the measurement noise as well as possible.
My understanding is that CGMs work best in the ranges that you calibrate them for. And - meter/strip systems’ accuracy is much worse when high or low than in the 80-120 range, where they are best. So I see two problems with calibrating high or low:
- you are getting the worst possible accuracy from the meter/strip system to measure from
- you are calibrating for a range where accuracy is less important to you.
If you read the Ponder book Sugar Surfing, btw, he spends a whole chapter on the need to calibrate well, and discusses specifically the reasons why you don’t want to calibrate high or low, but, instead, in-range.
Of course, as usual for diabetes practices, we should all be ready to go our own ways. But I think it is useful to discuss pros and cons so that everyone can make an informed opinion!
Looks like you’re well on your way to being a vet at this CGM thing. Having a child, age 2, who it type 1 and wears the G5 (and has worn it for about 4 months now), I can tell you it will help tremendously, with peace of mind if nothing else.
The one thing I haven’t read which is very important is to NEVER shut down the CGM when changing sensors! Only ‘Stop Sensor’, but never ‘shutdown’ the CGM during this process, or you’ll get an ERR121 error (learn from mine, and others, mistakes in this regard.) Just trust us! ‘Stop Sensor’ when you need to install a new sensor kit, and ‘Start Sensor’ when it’s been successfully changed out.
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Not at all! I was just suggesting that you may be able to get away with doing it suboptimally and still get good results.
I agree that using two different blood drops is better. Sometimes I get a big drop of blood and it seems a shame to waste it and then stab myself s second time. However, I am less sure about the reason to carry out the two reading at least 10 mins apart. The Animas DSN who trained me originally made no mention of this.
I agree that meter accuracy drops off a bit when well outside the optimum range, but it should still be pretty good at 70 or even 60 and similarly at 200. I always try to calibrate near bedtime - my BG is more likely to be close to the target range than say 2 hours after dinner, If it is not, I probably will want to glance at the reading during the night and I don’t want to have to faff with multiple button presses. Similarly, I don’t really want to have to get up and do a fingerstick just to calibrate the CGM.
TBH, the CGM is usually close to spot on, even with my sloppy attitude to calibrating. The objective is to use it as a safety net against hypos and to make life as easy as possible for me.
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My son does the same too:-)[quote=“jjm335, post:25, topic:58258”]
you may be able to get away with doing it suboptimally and still get good results.
[/quote]
That’s a very valuable lesson! it’s really good to know that if, for some reason, you can’t be doing spot-on calibrating, you may still not be too far off.
What does the end of a G5 sensors life usually look like? Sudden death or gradually less responsiveness and less accurate blood sugars to the point that the user decides it’s past it’s useful life?
Hi @Sam19,
for us there are two syndromes:
- we lose too much of the patch adhesive: my son swims many times a week, it is harder to keep the adhesive working. We use many tricks and 3rd party adhesives to keep it working long enough.
- the sensor becomes progressively noisier and its output less smooth. We get unexplained signal drops that take longer to come back. The worst is getting deep lows that are not lows, but spurious signal - when you ground-truth it with strips, they are not real (same as what you would see for a pressure low, except you did not put pressure on the sensor). The accuracy also appears to decrease right at the very end, but it is secondary to the rest.
After a while, it is too frustrating to endure. With a kid, of course, I am readier to switch early. For us (remember - frequent swimming), typically a sensor lasts 2 weeks, but we have had several sensors that have lasted less, depending on location. We are trying a new site right now, we are 9 days into it, and I have a feeling that we are going to pull it in the next 2 days.
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For me, they die slowly over a few days. More scatter in the readings as opposed to the smoothly curving plots
usually means I’m at the beginning of the end, with more dropped signals for increasingly longer duration sometimes starting at around the same time. Once they reach that point, restarting at day 14 or frequent calibration does not seem to rejuvenate them. One other thing I’ve noticed within a day or 2 of sensor death is dropped signals on the Dex receiver while the iPhone still picks up the signal.
Only times I’ve had a sensor die suddenly were caused by worn out adhesion, usually at one end or the other allowing some wiggle.
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Thanks John… I’ve been having a lot of trouble with the Bluetooth connection to my phone, but rock-solid connection to the receiver. I’m not sure why. I’d much rather rely on the phone since it auto uploads the data to clarity… and I’m not really in the habit of carrying a computer everywhere to upload the receiver data (don’t even own one actually).
I’m struggling to understand why the sensor being near the end of life causes less reliable Bluetooth connection… after all it’s the same Bluetooth transmitter isn’t it?
It is not my experience that the BT gets any worse. For us, when we get drops, the sensor signal becomes poor and the transmitter can’t make enough sense of it to actually send a data point.
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So we finally got the CGM last week and I am amazed already at the improvements in my son’s blood sugars. He was living at a 250 to 300 much of the time I believe, and now in the past week his average BG has been 180, which is a remarkable improvement for him. There’s certainly still room for improvement and we’ll get there, but it’s a good start!
The sensor insertion turned out to be remarkably easy, which has been encouraging. We put the first one on his abdomen and used an Opsite flexifix “patch” to help it adhere, but he managed to rip that one off before it had even finished the first 2-hour warmup period. Needless to say, I was not very happy with him! We re-inserted in his arm and this has worked much better - this second sensor lasted 5 days before getting pulled out by accident. He is very rambunctious and we’ve explained that he needs to be careful of his sensor, so hopefully these accidents that rip out his sensors will stop happening once he’s become more mindful of the fact that he needs to be more careful. He’s now on sensor number 3 this week - we won’t be able to afford this at this rate!! I tried Dextape and found that it peeled off within an hour, so I probably won’t use that again. Not sure why this happened… I’ve just ordered some Skintac, although I’m finding that the Flexifix does a pretty good job of keeping the sensor firmly in place for normal use.
I’m amazed at the accuracy of the Dexcom - it’s generally within about 5% of his blood glucose readings, and we’ve caught some prolonged low phases as a result. Last night took 3 juice boxes just to get him to stay in the low 100s, and I wonder if we’ve been missing low events. He was at 110 at bedtime, and dropped to 55 (confirmed by fingersticks) within an hour - I spent the next 3 hours battling to keep him in a safe range. Thank goodness for the CGM which alerted us to the fact that he kept dropping! Normally I would have checked him at bedtime, then again at midnight, but he could have been dangerously low at that point if we hadn’t been able to see that he was dropping.
Thank you all for your calibration recommendations and advice - it’s helped us learn quickly how best to calibrate and so far has made this a great experience for us. I’m looking forward to seeing what his next HA1c is!
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Such great news!
Your post is awesome, this is thrilling!
My son also became a lot more careful with his sensor after a few weeks. We do tape it with more adhesive. FYI, because my son is in sports we use thighs (a lot of people use arms), and we sometimes wrap it with horse tape if we are worried it might rip.
Every time I have called dexcom about a sensor problem they have sent me an extra sensor.
Mazel Tov for the wonderful start! The Dexcom is a life changer for a parent I think.
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I’ll have to give Dexcom a call and let them know we’ve had this problem - hopefully they’ll send an extra sensor. That’s a good tip - thanks! This truly is a life changer. I’m amazed at how much more aware he is now of his sugars, and it’s really kept his snacking in check so far. He doesn’t like to see the double arrow when he’s rising quickly! 
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My receiver is pretty beat up from dropping it, etc. so it’s possible it’s the root of this reception problem. At any rate, I’ve had data that is picked up by iPhone but missed by receiver, most frequently when the sensor is also getting wigged out from old age.
Bought a new receiver so we’ll see how it goes with an unblemished one.
I think you should look at bands4life. The have some great arm, leg waist bands for kids and adults. They are very cute no have many designs that I’m sure your son will like. They help keep them in place so maybe you can get one to last the full week. There are a few different companies that make things like this, TallyGear is another one. Check it out and see if might help. Good luck and enjoy the knowledge this piece of equipment will give you. I love mine and wouldn’t be without it.
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Thank you for this suggestion (and sorry for my slow response!). This would certainly help to prevent Jacob from picking at the tape around his sensor. We’ve started using SkinTac, which certainly helps, and have also started using DexTape. The SkinTac seems to help with skin sensitivity, which is great. But I’ve discovered the real problem is that he is purposely peeling the tape around the edges, which is very frustrating!!
At least the bands4life would keep it covered up so that he couldn’t get to it as easily. We are now managing to get a week per sensor, although just barely because he keeps fiddling with the tape. I called Dexcom and asked for tips to help the sensor stick better and they did send me two replacements at no charge, which was wonderful!
Thanks again for the tip!
http://www.bands4life.net/
(link added by @MarieB)
@rgcainmd, I love this, thanks for sharing. Here’s my only edit:
CALIBRATING YOUR DEXCOM G5 (or G-whatever 
)
LOL!
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Hi all, technical question
Does the G5 monitor work with G4 transmitter?
If the G4 transmitter works with G4 monitor with share , does this mean it work with the G5 monitor??
Thanks
The G5 receiver will work with a G4 transmitter, and a G4 transmitter will also work with a G5 receiver. The only difference is the G5 transmitter has blue tooth so it can also transmit to a smart device, independent of the receiver.