Dexcom trust?

Hey there, I’m struggling a bit with not trusting the readings I get from my Dexcom sensor, it will be accurate most of the time but sometimes it is very innacurate and I’m worried to bolus off of the Dexcom readings alone and find myself manually checking before I eat, any one have tips of how to deal with this? Thanks

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Sounds like you are dealing with it just fine. The only thing to do is to check with a finger stick. Trust will come with time and experience. If not, then you will continue to double check… pricey, a bother, but I don’t think there is any way around it. Besides, both the Dex sensors as well as finger sticks are less accurate in higher and lower BG ranges. You just have to keep your body able to identify where you are and watch the trend arrows. That’s pretty much all one can do.


@Adele, I am in my 11 month with the Dexcom G6 system. I learned to do finger sticks if the readings looked odd considering food and activity. I had more false readings with the sensor in the approved abdomen location.

The last 4 sensors have been on the back of my upper arm. These have been stellar.

I’m not suggesting that you do that, but if you do and have a sensor and/or transmitter failure, lie to the Dexcom tech. “It is on my abdomen.” :wink: :wink: :wink:


What sort of differences concern you the most? 100 vs 119? 239 vs 270?

I am content to have are Dexcom be with 20 of a fingerstick reading, when bg is in normal ballpark (say 80-140). If bg is rapidly swinging, the CGM will be behind by at least twenty minutes.That’s just the biochemistry of fingerstick vs interstitial fluid.


Experience of one year on Dexcom: it is almost always very close to my finger stick test. The few times it’s been off have related to compression lows (I’m lying directly on it at night and get woken up with a low alert) or rapid changes (I get an alert but it is lagging my actual blood value by 15 or 20 minutes). I have not yet had a high value that was not confirmed when I confirm check.
One thing I’ve noticed is that it takes a lot more insulin to correct a high than I would expect based upon my usual correction factor. Which is irritating. But has led to under-dosing (sometimes followed by frustration-dosing when it felt like the insulin “just isn’t working”) at times, something to be aware of.


Thankyou all for the replies it helps my confidence❤️

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I found that if I just stop doing finger stick, I’m happier.
Only when I’m sure it’s a bad sensor, I’ll check it. I don’t worry about readings taht are 20 off because the finger stick meters are not accurate and they test different fluid than the dexcom does so there is a delay.

Eventually I stopped checking it, only if I feel weird or it’s asking to deliver more than I expect.

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One thing to watch out for (and you may already be aware of this, but for completeness’ sake…)
If your glucose is changing rapidly for one of your tests (of either kind!), the Dexcom number will trail the (“true”) meter value in time. For me it’s 20-40 minutes; i.e., if I see a rising meter value, the Dexcom won’t show the same rise for that long. You can expect the two to be fairly close only if your blood glucose has been fairly stable for the past 20-40 minutes or so. This happens because the Dexcom ISN’T measuring BG: it’s measuring interstitial fluid (fluid between your cells), which is affected by blood glucose but lags behind it.
Sorry if this is old news! :slight_smile:


My Dexcom is almost always spot on. Once every 1 or 2 months, I will get a bizarre drop of like 50 pts in a 15 minute period in the middle of the night when I’ve not had insulin bolus for a 5+ hours. I just wait a bit and it jumps back to normal.

We have had similar mistrust, especially when (without a compression low), my daughter’s Dexvom reads 44 straight arrow down but the fingerstick says 112. I lose faith in it then too. In fact, I have her double-check with a finger stick often when the Dex says she’s going low. Mostly it’s correct but I still feel compelled to have her doublecheck. The Dex is especially erratic when we are getting close to the 10 day mark.

Her endo says that many of her patients have been having issues with the G6. I hope the G7 will be better

Laying on the sensor can cause false readings. I’ve experienced this before and the Dexcom site says to place the sensor where it is “unlikely to be bumped, pushed, or laid on while sleeping.”

I try not to place it where I will be sitting or laying up against it.

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I get the Dexcom to read within 5 points, but it takes a few calibrations within the first 24-36 hours, especially a brand new sensor. I always calibrate it when my BG level is around my target number 95-105. That is the range I want it to be the most accurate for dosing etc. I just don’t expect it to be accurate when it’s at 150 or 160. Those numbers accuracy don’t matter to me because I either know why I am at those numbers or aggressively trying to bring down those numbers. If I am trying to bring down those numbers I am dosing as needed. Sugar Surfing.


My experience is the same as Marie20’s – sometimes a new sensor needs to be calibrated with a meter one or more times during that first day. Other times, it starts out accurate and stays that way. In either case, once properly calibrated, The Dexcom readings have been well within expected margin of error.

OK, I guess once I bumped the sensor and must have moved it a bit, and then readings were eratic and I had to install a new sensor. Mea culpa.

One important suggestion – calibrate with a meter only when your BG is not changing either up or down. Calibrate only when it is stable.

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I use my meter more on the first day because the readings tend to be unreliable.

I don’t calibrate the first day and that generally works well for me with things lining up on the second day. I find that calibrating on the first day seems to create more problems overall. I’m better off letting things settle over the first 24 hours or so.

If I’m still off after 24 hours then I’ll calibrate. I’ve had one or two sensors that had problems after that, but overall holding off on calibrating in the first 24 hours seems to work best for me.


Same here. Pretty much a routine for me to calibrate within the first hour and then again a bit later on during the first day. Seems to calm the first-day wobbles and doesn’t seem to do any harm.

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I’ve been using the Dexcom for many years. Sometimes it is accurate and sometimes it is inaccurate. I always do a finger stick before insulin bolus. I use the Dexcom mainly for it’s alarm feature because I have hypoglycemic unawareness.


I do a finger stick most mornings before breakfast. I calibrate when the readings differ by more than 20 points. I don’t care which device (G6 or BG) is “more” accurate, I just want them to agree. For the most part, I calibrate 0-2 times each sensor.

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The one thing they didn’t tell me is that when you first put the Dexcom on for the 10 day period, it way, way under reports blood sugars. I laugh when I see advertisers saying “you’ll never have to do a finger stick again.” Ha! I do one every night to be sure. You will have a very difficult time convincing the Dexcom that your meter is right when they are way off in numbers, it usually takes three or four times of doing a finger stick to convince them that they are off.

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I wonder if your variability relates to positioning of the sensor?
After the first one, I put mine on the back of my arms.
Every time I’ve checked it’s been within 5% of my accucheck. (Unless I was lying on the sensor, or it was undergoing rapid changes).

I’m finding my Dexcom to be accurate, if I take into consideration that it lags behind a blood stick by 5-10 minutes (maybe more?). If I’m having a low, neither method is consistent - two finger sticks right after each other can be inconsistent. So if I am having a low, I use both until I know I’m out of trouble, otherwise bolus based on the Dexcom reading, frequently. My H1AC and time in range have both improved a lot doing it this way, so OK. It’s not perfect.