Dexcom Not 30-40 points off BG reading

Hello Everyone, I'm not sure if this has already been discussed but I couldn't find it. My son got his Dexcom on Tuesday evening and we were BEYOND excited!! We were up and ready to go by 7:00 pm. I have been reading that it takes about 24 hours to really get accurate numbers so I thought that last night around bedtime we would be pretty close to accurate. We are not :( Last night his Dexcom gave a reading of 194...and his meter gave a reading of 270. Also when he woke up today his Dexcom showed that he was 164 and his meter gave a reading of 210. Is this normal? Shouldn't we be getting numbers that are closer to the meter? I'm just wondering how long it should take. So far he has had it on for 36 hours. Any tips would be greatly appreciated. Also....I know the is says not to use Dex numbers for dosing...but is anyone able to actually get close enough numbers that they are able to use Dex? My son is only 7 and I know he wants a little break from finger sticks. I know he will still have to a few times a day...but it would be great if we could lessen the finger sticks and rely on Dex numbers. Thank you so much!!

My #1 tip to accurate readings: calibrate when level

I’m sorry your numbers are off. Mine are good from the get go most times. I dose almost solely off my G4. Very rarely do I cross check it. I calibrate when I am all over the map – unlike Andy’s experience, it just doesn’t seem to matter to me.


For me, it's not entirely abnormal to get variation between the 7+ and my meter. Heck, I just got two FreeStyle meters with my OmniPod and the FreeStyle meters were giving pretty different readings from the two OneTouch meters I had been using every day. The FreeStyle strips require less blood, which is a plus.

I've had my current sensor in for about 10 days. Just this morning, my meter said 152 when the Dexcom read 130, or something like that. Yesterday, I had a roller coaster - very high & very low - my Dex was off by more. Sometimes my Dex says below 55, when my meter says 80. Sometimes my Dex says 240 when my meter reads 180 - even if the sensor has been in for a while. With that said, most days it is very accurate. Some days, it is extremely accurate.

There are a couple threads on this site discussing the best way to calibrate the Dexcom - basically, how frequently to enter your meter readings. It seems that Dexcom representatives do not have a consistent answer either. In reading those threads, you'll find logical explanations for calibrating more frequently and also for calibrating less frequently.

So, there probably isn't "one" answer you'll find for your situation, without a little trial and error.

I think most Dex users would agree that the Dex will probably be less accurate when your son's BG is changing rapidly and also when it's high.

Personally, I still use a meter in most cases before a bolus. However, in a pinch I'll rely on the Dexcom. That's a lot easier to do if my BG is stable. I also have the advantage of knowing how I feel - whereas you need to rely on your son to tell you that. Overall, I think the best benefit I got from my Dexcom is recognizing the trends - namely the impact of food and exercise on my BG.

I've never minded pricking my fingers, but there may be some folks here can offer some tips on other places to get blood - places with fewer nerve endings than fingertips.

Don’t forget that the G4 is a directional tool, not an exact tool. I also tend to use it for the arrows function. I like to know which way my glucose is trending. Keep in mind you may experience a 20% +/- variance between meter and G4 readings. This is normal. The last sensor I had on for 19 days was pretty much closer to my meter reading after day 3. I will say that sudden spikes in my glucose will not be captured on the G4 for at least 15 minutes. (I will usually see a large delta between my readings when this happens.) So just be aware of the carbs that are being ingested and how it might impact the readings. These are my thoughts.

Hi - I personally think nighttime is the worst time to do it. The first day of use for the Dex has always been better if you can train it to match you. (Though I have to admit the G4 has been great at getting it right.) I usually finger test throughout at least the first 6 hours, if not longer, to make sure it's following along. I don't mean alot - like every 1/2 hour but like every 2 hours for sure and more if you think it's wrong. After the first day, you should be just fine. Good luck! I love the G4 - much better product than the Dex7. I was amazed.

The key in my opinion is that, as Laura said, you probably want to start/restart a new sensor early in the day rather than later. The reason is that you want to fingerstick A LOT (at least 6-10 times depending on how much day you have left) during that first day in order to get the G4 on track.

If you want to limit the number of fingersticks (which I wouldn't recommend during day 1 or 7) it might make more sense to enter fingerstick values while BG is level. But, in my experience, more is better in the first day. As long as at least some of the values are from level BGs, the G4 really is quite good at rolling with the punches and making use of values that are angling up or down.

As a general rule, the more BG entries, the better during days 1 and 7.

I second that, I did a little experiment to compare calibration to dex reading, then wait 10 minutes and look at the dex, it is generally for us less than three points off... speaks to the lag, for us about 10 minutes...

we have been dosing off the g4 also, just not any correction over our arbitrarily chosen 200bg... anyone else doing this? I was afraid to mention, cause i know it's off label...

Edit: This of course doesn't mean 6-10 fingersticks right on top of each other; it means distributed throughout the day.

Do you have the 7 plus or the G4? I have the 7 plus and I would NEVER take any insulin to correct without doing a finger stick. I have used the Dex7+ since August and sometimes it is right on, but at other times, it is WAY OFF. It sometimes reads LOW when my bs is 80-100+ or read over 300 when my bs is 200 or less. And that can happen at any time. It is so frustrating.

I am not sure if this is normal or not, but many times when I do enter a calibration, the receiver will be 30-40 off from the numer I just entered. I can be reading 130 and when I check my bs it is 134, but when I enter 134, the receiver changes and reads 160. Does this happen to anyone else?

I think you may get better readings with different sites. I am going to start keeping track of where I insert the sensor.

I am finding that the tape doesn't always stick very well. I am allergic to Tegaderm, so I am using IV3000 and cutting out and oval before I apply it, so I don't cover the transmitter.