How much is normal for the Dexcom to be off from the BG meter? I just started my very first sensor yesterday so I am still in the first 24hours, but it seems like the sensor readings are 20 points or more off of my meter results. Does it help to continue entering meter readings to the dexcom to help it be more accurate? Or should I just do the 2 per day and hope the accuracy improves? Any help is greatly appreciated.

Laramie, WY

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Hi Renea,
I'm a pretty new Dexcom user too, just a few months now, so others might have better info for you. So far, I've noticed that several of my sensors have been off in the first 24 hours, but after that things settle in and they are pretty accurate. But, I've also had several sensors also be totally accurate from the start, too. So, I think it just depends. But I think general consensus is to expect a bit of inaccuracy in the first 24 hours. Some people say that if you start up a sensor when your blood sugars are relatively stable, then you get better accuracy. Also, my dexcom reading seems to be about 10 minutes behind a finger stick reading. Anyway, I'm sure more experienced Dexcom users will pipe in with helpful info for you soon. I love my dexcom and have found it so helpful, I hope you do too!
This a good and valid question badly answered in the supplied documentation.

first off, the most accurate readings of ones blood is at fingertips. Next, Dexcom sensor depending where it is positioned
will provide readings differently than those of ones fingers. You will get accurate readings of the glucose of the sensor location which will vary from fingertips.

Sensor location is another factor. For me arms were best and abdomen useless. Many times on gut I would wake up with 160 on gut and fingertips - 230. Arm never showed such variance. I am unclear who idiot was who decided gut best. On another web site I found users who stated emphatically that gut useless and arms and other locations better.

Another factor not discussed is how fast does your BG shift around. If it is slowly moving like waves on placid lake, sensor on interstitial tissue will track much better than if your BG numbers move a lot and quickly.

i was on wrong insulin 75/25 that was booting my bg rail to rail and on slight exercise. Now on humalog lispro and no pills such as starlix/glyburide; BG far more stable and performance of Dexcom vastly better. Frequency response and data not given by dexcom and frankly they were unhelpful.

generally, interstitial tissues track slower than fingertips and result in differences of readings and slow tracking.

also, i typically find most times, dexcom agrees with freestyle lite meter within +/- 10 units except on change where the dexcom has to catch up. When sensor is getting to end of use, i usually see larger differences and extra changes in readings even though handheld is stable.

accuracy numbers stated from dexcom are unhelpful and industry should be shot over its
+/- 20 per cent excuse making.
today i am happier but through my own efforts and website such as this.. good luck
I sometimes see poor agreement until the third day. I think the site chosen on my body may have something to do with that. If there is any scar tissue at all hidden beneath the skin's surface, it can interfere. There are other things that can interfere as well.
I agree with the others. In the first couple of hours we pretty much ignore it completely, and after that, it still sometimes takes a day or two to be more accurate. But there are the sensors that are almost dead on from the beginning.
i also agree that first day on new sensor readings off and not helpful. I find by end of 10 hours tracking improves greatly.
I find that they usually do have to 'marinate' for a few hours up to a day. You will hear arguments for and against calibrating more than twice a day.

Remember not to base any dosing decisions on the dex reading - always do a fingerstick first. The technology is good but not great. I tend to think of mine more as an indicator or warning than an actual reading. That being said... I LOVE my dex ;)
I've used Dexcom for 4 years. The accuracy of the sensors vary hugely, though as everyone says, they get better after a day or two.

Here what I've learned. From Dexcom, only recalibrate if he reading is off by more than 20%, otherwise don't do another recalibration. Really try not to calibrate when your Blood Sugar is going up or down. I've found it better to wait an hour or two when blood sugars are stable. If the sensor is off by 100% up or 50% down (particularly more than once), call Dexcom and get a (free) replacement. They'll ask for a download of your data, so do that before you call.

The next generation of Dexcom is said to have MUCH better accuracy, but the idiots at Obama's FDA are stopping most medical devices from being improved since it is politically safer for them to withhold technology from the market. Europe is getting new medical devices 2 to 3 years before the US. I'm not sure what the downside is to having a more accurate Dexcom in the US market, but you'd have to ask the FDA morons that question.
Ok, here is a dumb question, but at the moment I just can't wrap my head around it. How do you calculate what percent the dexcom is off?
Re: recalibration guidelines. A Dexcom support rep told me that the 20% guideline applies to readings of 80 mg/dl or higher. For readings lower than 80 mg/dl, she said to recalibrate if the reading is +/- 20 units (which is more than 20%).
The FDA is not Obama's. Most are career civil servants or outside consultants. The rules are made by Congress and the last major changes in the approval process came under Bush. I hope crow tastes good!
Did Obama not nominate the current commissioner of the FDA Dr. Margaret Hamburg? It is my understanding she is the one who put the brakes on device approval as well as other things. A quick google search of Obama and FDA yielded:

In a Tuesday Wall Street Journal op-ed piece, President Obama announced a newly signed executive order that pushes for more efficient regulation throughout government agencies, including the FDA. "The FDA will lay out a new effort to improve the process for approving medical devices, to keep patients safer while getting innovative and life-saving products to market faster," Obama explained. But the new guidelines had some in the community worried as they wait to hear how the changes would be implemented.

How are the rules made by Congress if Obama can sign an Executive Order that "pushes" for anything the FDA is doing? Seems as if the politics of the FDA aren't as simple as Congress makes the rules.
Why not leave Obama and politics out of this? The FDA has always been poor in this respect. That is what happens when an important organization is perpetually underfunded and not particularly well staffed with highly qualified people. Nobody is likely to fix this and doing away with the FDA is even more dangerous. Let's stick to the Dex.





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