Love Dexcom when it works...:-(

Hey all -

I’ve had the Dexcom 7 for about 3 weeks. Since then I have had 5 bad sensors, the receiver had a scratch screen when I got it (not a big deal until) I started getting dust under the top layer of the screen. There has been maybe 3 days where the Dexcom is accurate within 5-10 pts or even 20% of my meter. When that happens I absolutely love this device.

However, after my first 3 sensors failed yes, they sent me new ones, my 4th sensor lasted about a day of great readings until it stopped showing the arrow after going down 30-60 pts in 2 or 3 readings, showed me going up 300 when I was at 140, show me steady at 90 when I was in my 50’s etc.

I have tried doing the calibrations once every 15 minutes 3 times to see if that helps which it does for about an hour. I am just seeing if I am having bad luck or I’m doing something wrong.

Any tips appreciated


You dont want to over calibrate it. that will give inaccurate readings. I calibrate it when it tells me to unless I know my meter and monitor is way off and need to get it in sync.

Is there a chance that you are taking a medication which has acetminophen in it? I had trouble finding a pain reliever I could use because many, even prescription meds, have acetaminophen in them. Acetaminphen causes false highs.

I haven’t tried the every 15 minutes 3 times calibration method since Dexcom tech support told me about it.

What has Dex tech support suggested you try? Have you discussed with them? Ideas - sensor location sometimes makes a difference. Insert at night, do not start until morning - helps me a lot on the first day. Are you making sure the transmitter is snapped down correctly. I have read where if moisture gets under the transmitter, it will mess up readings. Are you inserting correctly? Is the sensor being compressed to tightly with clothing - Tech did tell me when I began that could cause a problem. Try not to sleep on it at night. Do you tend to have rapid swings in your sugar either up or down? I notice when I go nuts in either direction rapidly the Dex has trouble. Good luck!

Hey Ross

I am on my 4th week and I am having similar problems. I had 3 sensors replaced and constantly got the ???. When it works its amazing but when it doesn’t its super frustrating. The other issue is sometimes my Dex is spot on and other times it can show me a bg number within 50 pts…

I had those sort of frustrations when I first started two years ago. I’ve found that the Dex works best when I am well hydrated and moderately active (ie not sitting still for a long time). It also is highly variable in the first 24 hours. That is why some folks like to “season” the sensor by inserting it (say at bedtime) and not starting the calibration session until several hours later (say when you get up).

I will also echo some comments that you shouldn’t rely on fingersticks as the be all/end all in terms of accuracy. I’ve fingersticked over 110,000 times in my life (yes, one day I actually took out a calculator and tried to do an estimate) and I’ve come to expect that sometimes my One Touch will give odd readings. Here is a video I made a couple of years ago with an example:

I would also agree that over calibrating seems to have limited usefulness. In the first day in particular the Dex might jump all over the place, and it doesn’t seem to be helped by calibrating frequently.

Good luck and I hope things turn more positive for you.

Hi Ross, I have had the Dexacom for a year now and have learned not to expect too much out of it. It is not fast enought to keep up with rapid swings, but the arrow will let me know which direction I am heading and how fast. For example if my Dex reads 90 but the arrow is pointing straight down I am looking for juice. The only time I get the ??? Is when the under skin sensor is not seated properly or has been bumped or tugged out of place. Sometimes I can do a finger stick, recalibrate, wait, and the ??? Will go away. Usually it means that the sensor is out or bent. I have heard that using I.V. prep can cause false readings, so I only use alcohol. I like the Dex and would never want to go back, but its numbers often lag. I still check my bg with finger stick several times a day and calibrate each time which makes the Dex more accurate the longer its in.

Thanks for the replies all I will try to answer all questions in this thread.

In regards to rapid fluctionations, I do not believe I have any. My A1C’s are always low 6’s or high 5’s. Here is a graph (below) of my 24hr dexcom and was accurate as I was testing about every hour and it was within 5 to 10 points.

I am currently talking with Dexcom support later today as they need me to upload my information. I am inserting correctly and on the fattest part of my bodies as possible, stomach. I am not taking any medications that would mess up the readings per Dexcom.

In regards to readings, even with rapid fluctionations when it was working it was spot on, If I was going up double arrow or low arrow I was still within 5 - 10 points of my meter. My biggest problem now is after about a day of use it will show up arrows when I’m going down or is off by 100 points, or my start up of a new sensor won’t even work. I am really hoping it is just the transmitter as I stated above I love this device when it does work and is accurate. The first week I got used to using the arrows as if I’m dropping fast go to juice, or going up fast above 140 need more insulin, but I stopped doing that since I had a 212 double up arrow took insulin then tested a min after and was at 115 so since then I can’t trust this system as I want to.