BG readings WAY different left vs right hands vs Dexcom G5- messing with insulin dosing!

My finger stick BG readings are insanely different from one hand to the other. I also have the Dexcom G5 (which trends very low vs my finger stick readings)
My left hand always reads higher than my right hand BUT it’s the difference that’s concerning.

Right this minute My left hand reads 197 and my right hand is reading 108. My G5 (which is on my right arm this week) is, at this moment, giving me an Urgent Low alarm telling me I’m at 55. (I’ve also come to realize the Urgent Low’s from the G5 usually Mean I’m running about 80, NOT 55 or below as it is showing)
I’m so confused by the different readings between my left and right hand. I prep my fingers the same way, with alcohol pad, let dry, then stick using a new needle each time. My readings this morning between the two hands were 254 (left) and 167 (right)…just seems like a BIG difference there consistently.
Anyone else experienced this? How in the H-E-Double Hockey Sticks do I calculate insulin needs with three readings being so all over the place?? We currently have my ratio set at 1:3 but how do I determine which of the three readings are “correct?” (Left vs Right vs G5 Monitor) Any ideas my experienced friends??

Type of meter you are using? I’d start with that. Google Gary Scheiner’s meter accuracy ratings.


Take your meter to next endo visit and test it against theirs see how bad it is off. May be time for a new one or brand.

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I strongly urge you to stop using alcohol swabs on your fingertips. If you think your hands aren’t clean enough just wash them with some soap and water and dry them. Repeated use of alcohol on your fingertips is going to be detrimental to your skin. And what meter are you using?

Make darn sure you are well hydrated if you want the Dexcom to work well and if you keep having trouble with the Dexcom on your arm put it on your abdomen and try that

Thank you all for the input! I didn’t know about the alcohol wipes , it’s what I’ve always been told to use. I will stop and see if my readings change. Dexcom has been a bit of a nightmare- never seems particularly “accurate,” Regardless of where it’s located. I still use my Contour next EZ meter more than I should have to with a CGM.
I see my endo for the first time on 11/27. We shall see what she thinks about everything, hoping to get a pump soon!

Contour is a top-notch meter. If you are seeing quirky numbers like that it might be something on your fingers.

The meters themselves are very cheap. Might be good to get another one and compare.

Wash and dry fingers.

The Contour meters are superb so that won’t be a problem for you. I have the Contour EZ, Link and One. They all match each other

This is certainly baffling and I agree with some of the suggestions others have posted. But here are a few things I would try:

First, contact the Contour Next Rep and describe your issue. They may have some helpful suggestions. If you have a second brand of meter, contact that Rep as well.

Do your testing at times when you expect your BS to be stable. Even a minute or two can make a difference if things are changing rapidly.

Do you always do your tests in the same order? If so, try reversing the order and see what happens. Better yet, do a L-R-L series of tests. Does the second left come back to the original value? Or reverse this and do R-L-R.

I’ve read that sometimes high levels of certain chemistry in the blood (other than sugar) can affect readings. I would expect those to be the same in both left and right hands though. Still, trying a second meter of another brand might be helpful.

Some of these tests are beyond what I would normally do. But your results are beyond what most of us get. So, a little extra detective work is certainly in order.


I have a suggestion that may help if contamination (soap, lotion, sweat, etc) is a possible explanation for the discrepancies. I sometimes have to check my BG without an opportunity to wash my hands (mid-lecture in my college classroom, for example). My endo recommended blotting away the first blood drop from a finger stick (with a tissue) and then testing the second drop at the site. This eliminates much of the potential contamination.

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Hi Kori:

I also had a similar problem when started taking readings on 2 hands but not to your extent, more like difference of about 40 and had used Lifescan Ultra 2 system for years. I wash hands but no alcohol. When my mail order supplier went out of business, I changed to the Contour meter and the problem fixed itself so maybe check using another meter. Readings are always very accurate down to about 100 but after that I have huge differences between finger stick and Dexcom CGM. Same issue where CGM blares at 55 or lower when fingerstick will be in 80-90 range. My guess, and it is just a guess is that the algorithm Dexcom wrote is linear and follows fingerstick values down to about 100 but after that Dexcom uses an aggressive curve to show you much lower than you really are. My average glucose reading over 7/14/30/90 days is 100 so I am quite familiar with this problem. Again my guess is that Dexcom had an option to be tied to the Animas pump and that when you went under 100 or so they wanted to make sure pump would not continue to deliver insulin sending you into a low. Dexcom is a corporation and could be held liable if their system allowed you to die from a hypoglycemic episode. Years ago, and I don’t know if it has changed a similar experience with the airlines, I would order a diabetic meal and glucose would go through the roof. Makes sense that the last problem an airline wants is to have a diabetic have a hypoglycemic event during a flight so have just been eating regular meals and dosing for those.

I also found placement of sensor affects CGM readings at night but that is another issue.

I’m not sure I can get on board with the voracity of that statement. Have you got ANY information that Dexcom, OR ANY METER company on the planet has EVER been successfully sued for their equipment’s readings??? My god, I can be in the 30’s or 40’s (dropping VERY VERY FAST), and there is NO way that any CGM can keep up with the drop, to show, in REAL TIME, that I’m that low. Give it another 15 minutes, or more, and the CGM may very well indicate the severe hypo, and by extension, continue to show a hypo, when I’ve already gone back up into the safe zone of well over 70-100 by eating a bunch of carbs. It’s well known that a super fast low can’t be shown in real time on a CGM due to the interstitial delay that is introduced into the mix. And put ALL that aside for a moment, and realize that you might be very low, and YOU DIDN’T HEAR/FEEL an alarm because of ambient noise, you are deaf in one ear and slept on your good ear (like me), or a zillion other scenarios. Now put all THAT aside, and know that it’s pretty much impossible to hold culpable a company that sells a product that is used as an ADJUNCT to helping monitor INTERSTITIAL FLUID glucose values. We aren’t talking about a car that has it’s steering wheel suddenly fall off because the mfgr used inferior attachment hardware.