At what point do you change your sensor?

just curious about how “in range” you consider your sensor to be compared to your finger sticks w/ your meter. how often do you find yourself considering your sensor a dud and taking it off and replacing it? do you just continue to calibrate, or do you feel its too unreliable and there is no point in wearing it anymore?

i was told (from members on the TuD site) that the first 24 hours can be a bit wacky and to be patient and it will steady out and become more accurate.

i use a dexom cgm, which is, often unreliable depending on where the sensor is located, but the dexcom co replaces the dud for free, and, they will over-night it via FedEx.

For Enlites, when the ISIG’s are too low to enable proper calibration. It’s pretty obvious (at least to me) when a sensor’s ISIG is so low as to be useless.

I find the Dexcom generally VERY reliable after the first 8-12 hours. Also, like many. I find it even more reliable the second week and even third than the first. When I start to see wild numbers or several breaks (for ??? and lost of siignal), I know it’s done.

I do like Thas. If I start getting ???, or the numbers seem off, I know it’s time to change.

what is an ISIG? i don’t know about the Enlites. mine is a Dexcom. how are they different?

so if i put my new sensor on yesterday evening, it wouldn’t be unusual for it to be a little wacky now? i don’t want to take off a perfectly good sensor and start the entire sensor session again just for the hell of it. and even though dexcom will replace it for free, i am still over-checking w/ my test strips and using up my very expensive Tegaderm. i know we are not all doctors here, but would you suggest i wait it out a little bit longer to see if my calibrations begin to pull all my BG numbers together, in sync?

how often do you get the ???. sometimes i get them after i shower. i am impatient and don’t want to wait 3 hours before i pull off my sensor. it only goes down hill from there. also, how soon might you get your numbers to be “off?”

There is no point in my explaining ISIG’s to someone not using Enlites. And for those that do use Enlites and want to learn about ISIG, the best thing to do is spend a few hours here and there talking to some of the better MM tech support people about the ins and outs of ISIG’s.

Let’s try it from another direction. How much of an overview do you want about the mechanisms underlying how a glucose sensor works? If you’re still interested after reading the article linked below which is targeted at the general diabetes aware public, then we can always talk about it more.

“Anatomy of a CGM Sensor” by Erika Gebel Berg, PhD, May 2014 issue of Diabetes Forecast

The part of the article which pertains to ISIGs is this.

The sensor uses the same enzyme to measure glucose levels as a test strip: glucose oxidase. This enzyme converts glucose to hydrogen peroxide. The peroxide reacts with platinum inside the sensor, generating an electrical signal that travels through a tiny wire to the transmitter.

That “electrical signal” is what the ISIG is. It’s just an amount of electrical current measured in nano Amps. The amount of current is assumed to be directly proportional to the amount of (interstitial) glucose. When you calibrate your CGM all you are doing is training it to “guess” the value of a “Calibration Factor” to multiply the current from the sensor (ISIG) with to get a glucose value.
      [Sensor Glucose] = ISIG * [Calibration Factor]

Medtronic exposes the values of the ISIG. My understanding is that the Dexcom system does not. I expect it is still there, just hidden “under the covers”.

I use my sensor more for its trends than for its exact readings, and therefore do not expect it to be truly reliable in terms of blood glucose readings. There’s a reason that it isn’t yet allowed to replace fingersticks. If my Dexcom alarms that I’m high or low, I try to test before taking any action with insulin or carbohydartes. If my Dexcom is reading within 1 mmol/L of my meter (18 mg/dl), then I consider that very good. Often it’s more like 1.5 mmol/L (27 mg/dl) off, and at times has been as much as 3 mmol/L (54 mg/dl) off. I just calibrate and continue on. A few times it’s been off by 5 mmol/L (90 mg/dl), which I consider pretty inaccurate and start wondering about the sensor if it happens repeatedly.

Since I pay for my own sensors, though, I push them to their limit and wait until I have a 24 hour period where I have more ??? than actual readings before I change it. Often, even when they are doing that I’ll restart the same sensor and hope that it will come back (I’ve had it happen once or twice), and only change it if the restart doesn’t help. It means hours without readings, but even Dexcom technical support will tell you to let a sensor wtih ??? run for three hours or so before changing it, because it takes that long for the computer algorithms to try to work through whatever interferance is causing the ??? to appear.

For example, this is the day leading up to my last sensor change. The previous day had additional periods with no data, and when data did appear it was significantly off (by 5 mmol/L). I was unable to calibrate more than once on that day because the data wasn’t there when it asked, so I finally just decided (reluctantly) to change it. I think if I wasn’t paying $85 per sensor, I’d probably change them a couple of days sooner than I do, but I’m always hoping it’ll recover and come back.

i understand that you are paying out of pocket, but the Dexcom Tech Support will replace any defective sensor for free. what i do, is i save EVERY sensor package i open. then, if i have a problem, i can have access to the LOT # of the particular sensor (not that Dexcom cares so much, but its good to have it handy). they FedEx me a replacement overnight. today was a particularly bad day for me w/ my sensors. first i had terrible calibrations for a couple of days; WAY OFF: sensor read 380 and my fingerstick/meter showed 131. i do do the recalibrations, but with this sensor nothing was working/cooperating. i finally took it out and put in another new one. this one hurt like hell at the sensor site, so i pulled that one out. i put in a third one, it felt fine, and then an hour later i got an alarm on the receiver saying “sensor failure.” so i took that one out. i called up the tech support and they replaced all four of them. they were incredibly helpful and apologetic, and they told me that if my endo prescribed putting in the sensor in a different part of my body, that they (dexcom) would still stand behind their product, which i greatly appreciated. i am very very lean so i often get problems w/ finding a successful sensor site. but as i call dexcom regularly, they don’t seem to mind at all. their immediate answer is “we’re sorry you had to go through this; i will be happy to replace your sensor.”

maybe this will help you; i hope so.

Thanks for the information. It does sound like you have a lot of problems finding a good spot for your sensors. My sensors are usually fine for 1-2 weeks, and it’s during the third week they have problems, and almost never last beyond 18-20 days. Unfortuantely, past the first week Dexcom won’t replace them. I did call them once about a sensor that was inaccurate, but they just walked me through recalibrating it, and said if it was still inaccurate after that they would replace it (fortunately, it was fine). I hear of some people wearing sensors for more than a month, and just wish I was one who could do that!!

the general rule of thumb w/ Dexcom is that they will insist that you try recallibrating it 3 separate times at 15 minute intervals. if you find that your calibrations are still not working, they will immediately replace the sensor. (of course if you have so much as pain, however small, when you insert or wear one, they will replace them, too) if you just let them know that you have tried out their recalibration process and found no success (however minor), they will ship one to you over-night.

just for your own info. you need not be miserly or uncomfortable. Dexcom stands behind their product 100% no matter your problem. take advantage of this whenever you need to. you deserve to be treated w/ respect and they offer it.

John, thanks for all the info. i found it interesting and informative.


Thanks for the info. Dexcom only stnads behind their product for the first week of wear (since that’s all that’s approved for a sensor). Since I wear most sensors for two or three weeks (or more, if it lasts), and usaully don’t encounter problems until the last few days of that period, they wouldn’t replace it. I don’t think I’ve had a sensor be anything more than mildly uncomfortable (and by “mildly” I mean I notice it’s there, but it doesn’t exactly hurt). What I do have problems with is infusion sets—wish those companies would replace sets that are painful or are put in sites that don’t work! I don’t pay for those, though.

what i don’t understand about the situation w/ the packaging of infusion sets and the corresponding tubing is that they don’t just offer the infusion/introducer needles separately. i like to change my site more frequently than i fill up my pump and i find that i use up my sets b/c of this. and i have to say that when i have had problems w/ my infusion site, i call up Metronics and make a report and they send me out a replacement right away. have you tried that yet?

Some sets do have the tubing and infusion set part separately, or at least used to. When I used Cleo sets, those were packaged separately. But I know what you mean, the tubing sometimes piles up.

I havne’t tried calling Animas when I have problems with infusion sets. The infusion sets I use are not “their” sets, just distributed by them (plus, until recently, I got my infusion sets through my local pharmacy rather than through Animas). I never thought of calling them because, in my mind, it’s not their fault that I’m allergic to the material the sets are made of nor that I mgiht insert it in an area that isn’t the best. I use the metal sets, which are supposed to be nearly impervious to set issues, but I have times where I still get high blood sugar and ketones or where insertion is really painful and I have to move it and eventually insert a new one (usually I try moving it 2-3 times before getting a new one).

Is it common for the pump companies to replace infusion sets that are “bad”? If so, I don’t think it’s common knowledge, as a lot of people have problems with kinked cannulas or sites that don’t work for other reasons.

My practice has long been, but I may be changing it, is to wear the sensor for as long as possible but my last sensor was not within 20 points of accuracy at 100 as is the dexcom stated standard. So I put on a new one after one week and a couple days. And I’m trying to motivate myself to wear it for only a week. I’ve long thought the accuracy does not diminish but I now think it does. The last sensor was tracking fine and no ?s. Or gaps but I was blood checking and it was off by 30 and the expectation is for it to be more accurate. I was going two weeks because it allowed me to give gifts but there’s no need now. I thought that after the software upgrade the accuracy in second weeks was improved.

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What does it mean to give gifts

i dont understand your question, Karen. please explain