Dexcom g6 being off

We have been having issues with the dexcom G6 being 100 points or so higher than the finger stick the last few days at lunch time at school. It’s very strange because at home I find the dexcom to be pretty accurate. I have changed sensors, and still the readings are off. At home my readings have been accurate and I calibrate. Anyone have this happen?

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That would be far outside the working parameters for the G6, and I would be getting a new sensor if the behavior persists. With that being said, the fact that it is fine at home, but crazy at school makes me believe the finger stick technique might be lacking. Is your child of the age that this is even a possibility?

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That’s what I said to the nurse. My child is 6 and checking her own blood sugar at the nurses office. I asked the nurse to check a 2nd time. She did, but it was after lunch so carbs and insulin had already changing her blood sugar. I am proud my daughter is doing it herself, and want her to continue doing so,but wonder, since this seems so strange to me to be that off. We have now had this happen with a old sensor and new one, so I dont think it’s the sensor. Wonder if alcohol on the finger could be diluting the blood?

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@Nreid77 - Is she washing her hands with soap and water? If I have big differences between finger sticks and my G6 it is usually because I didn’t wash my hands.


No using an alcohol swab.

You might want to see if you can go to hand washing for a week, to see if it makes a difference. No telling what your daughter is touching at school. Lord knows my boys seemed to find the worst stuff all the time (sigh), even one time my son didn’t notice that the bathroom was flooded, waded in and slipped and cut open his chin on the sink edge. The nurses at the urgent care washed that thing out like 10 times.


Yeah, I will have her give that a try. Thank you.

Oh my goodness, @Chris.


@Nreid77, I also think it’s probably a matter of your daughter washing everything off her hands, but I’ll throw in another possibility on top of that… Is it 100 points off in either direction, or is the Dexcom 100 points lower? If it’s always lower than the meter, it could also be a very fast rise? Any chance your daughter is eating something that’s leading to a fast spike?

By the way, 6 and testing her own sugar… you really should be proud. :grin:


This would definitely be my son. No, I didn’t eat anything with a guilty look on his face.


You know how I know about that, right… :roll_eyes:

Never too old to “not have any idea why” my blood sugar is on the rise.


So her meter has been 100 points lower than the dex. The only other thing I could think is she has recess before testing, but today it was 130 points lower. Never have I seen that, even with exercise. They calibrated and then meter said no data for 1 hour. I think the dex was confused.


Which meter are you using? Is your daughter properly hydrated? The Dexcom sensors don’t give accurate readings if the user is not hydrated.


Can you do a fasting test with her in the morning? To see whether they’re having problems before she gets up and starts moving? Does she have relatively stable blood sugars in the morning?

Had a woman tell me about a similar problem about a week ago, and we kind of went over a few Possibilities. We decided to start with a baseline check to see if she just always had that kind of discrepancy. She was surprised to find her numbers were spot on in the morning and set off to look for things that may have been causing a rapid change in blood sugar like that. I have no idea if the same could maybe be true in your daughter’s case…

130 points on any sensor is drastic… but on the Dexcom, that’s really pretty crazy. I love to exercise and definitely have seen number discrepancies like that (especially on Medtronic), but I would think she might be able to report to you of recess really is that grueling? Just out of curiosity, is she doing any kind of bolus before recess? That could definitely explain a drop like that… maybe…

I’m here to go get answers about my own mysterious numbers, so I’ll get to it and leave you alone…

Right after I make an unsolicited suggestion… Can you have her replicate a recess type scenario over the weekend and do the testing yourself?


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We have done a fasting finger stick check in the AM and all normal. I also do one before school and it matches the dexcom pretty closely. No bolus before recess. And she says she doesnt run around that much at recess. Yes, I will keep an eye on it this weekend and test a bunch and see what I see. In my experience the dexcom catches up pretty quickly to real time blood sugar even with crazy excercise. Still scratching my head on this one.

Sometimes the obvious can elude us. I have an electrician friend who tells me I’d be amazed the number of times he’s called to “fix” a light. He changes a bulb and the company bills the homeowner for a service call and 1 hour of labor.

Obvious questions:

Same meter / strips or is a separate one kept at school?

Is the meter / strip bottle kept in a room temp spot? Not set on top of a fridge or somewhere that is too warm/cold?

Do you send wipes? Or is the school providing them? Are they both alcohol based or is one Benzethonium Chloride wipes? There can also be a big difference between the evaporation rate between a 70% isopropyl alcohol wipe and a 90% isopropyl alcohol wipe.

Years ago there was a debate / discussion about finger stick results being altered by residual water and/or alcohol. Not sure how or if that debate was ever resolved, but ultimately what it said to me was that I didn’t really need to obsess over a pristinely clean finger. Consequently, I haven’t used an alcohol wipe for that in decades (my wipes stock pile is almost as big as my lancet stockpile). Unless my hands are filthy, I just stab my finger with not even so much as a pass under the faucet.

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I had this happen and every time it does, I just call Dexcom customer support to troubleshoot and get it replaced.

This doesn’t work as well as running water. The meter is really sensitive to tiny quantities of sugar. So think about what happens to any sugar that is on the finger.

With running water, the sugar dissolves, and is rinsed away down the drain. With an alcohol swab, the alcohol+water from the pad flows to the finger to wet it, so sugar dissolves (but not so well because there’s less water). Where does the sugar go? Some transfers to the surface of the swab, but some just stays on the finger as the alcohol and water dissolve. The alcohol swab to some extent just moves the sugar around, rather than removing it from the finger.

Could you show us a sample graph from the Dex or Clarity? Maybe we could see something in the shape of the curve that would give a clue as to what’s happening. Also, what time was the insulin given and what time was the fingerstick measurement done?

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