FUDiabetes

Comparison between CGM and finger sticks

Is your CGM generally higher or lower than your finger sticks? I have Dexcom G6 and I can’t seem to distinguish a consistent pattern, sometimes the G6 is higher (seems like when BG is higher) and sometimes lower. Although they are fairly close, when I’m low even a small difference is important.

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Question for you. Is your BG stable when you make these observations. Because when your BG is changing, the CGM lags. For us, when my son’s BG is stable, the G6 is usually only off by a couple of points (Single digits), but when it is changing, then the sensor can be quite different from the actual.

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I keep a log book and write down every finger stick and the corresponding DexCom value. So I have comparisons both with steady BG and changing BG. (I actually take more finger sticks now that I have a CGM.) The finger sticks and CGM seem to be closer together at lower BG values and farther apart at higher BG values.

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That makes some sense in that if the sensor is off by 3% for instance, that would be smaller at the lower value than the higher. That hasn’t been our experience, but honestly, we have slacked way off on comparing since we have been on the sensors for a few years and the comparison takes some work, and we are lazy…

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I’m new to the CGM and so I guess I don’t completely trust it yet. lol

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With the G5, we trusted the track (up, down, flat) much more than the actual number. That info is worth a ton even if the number is wrong. With the G6 we trust the number as long as we are flat. We never trust the sensor number when things are changing. But knowing if you are trending up or down, or staying flat, is still really good info you don’t get from finger sticks.

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@Jan, it could be pure coincidence, but the patterns you describe are fairly common for me as well. And I’m not new to CGM. I absolutely agree with @Chris about the needing to be sure you’re stable—and I think it can be difficult to be sure a lot of the time. I do, however, still see the Dexcom (and Libre) overshoot my highs at times. A fast rising blood sugar in particular seems to catapult my sensor readings. One other thing to remember though is that the sensor reading can make up for that discrepancy in a single leap. So after I’ve tested and logged, I’ll usually look at the sensor every 5 minutes until I see if it’s caught up—or if it’s headed in completely the wrong direction.

I’m chatting with my kid and attempting this message, so I’m rambling. Sorry. It’s just my favorite topic. :grin: The last thing that comes to mind is your meter—which meter are you using?

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There’s a five minute lag. When my G6 is being accurate it will show the BG my fingerstick said 5 minutes earlier assuming it did not calibrate with that reading.

I don’t typically need to calibrate for the first 12-15 days, someone (eric, chris?) had said not to calibrate initially. I do notice significant instability in the readings in the first 24 hours.

After that (12-15 days) the sensor starts to drift and calibration seems to help, but not for long. Soon (within 20 days) the sensor gets increasingly large apparently random errors and I swap it out.

Dexcom’s 10 day limit seems about right for the G6, erring on the side of safety, although the 1 day instability at the start does, for me, justify sticking with the G6 for maybe 14 days :wink:

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@Nickyghaleb - I use the Accu-Chek Aviva meter.

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@jbowler - I restarted the sensor for the first time (previous sensor) and was able to get 20 full days out of it. I planned on doing a 2nd restart because the sensor seemed to be behaving, but ended up changing it due to physical discomfort. When I took it off I had a pretty good bruise under the sensor. Not sure what caused that, but I decided that if I could get about 20 days, I wouldn’t push it.

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Okay, I don’t know anything about the Accu-chek Aviva. I know some of my meters run a little higher or lower than others, but I’ve never used that one. So then I’m down to whatever else I said up there. I think those things still apply.

I also extend my sensors, @jbowler and @Jan. I’ve gotten long as 26 days… maybe longer. I extend for as long as it continues to perform without long breaks in readings. Once I see those growing gaps, I pull it. I regularly get up to 15 days and fairly frequently get around 20. Just extended one today and will be lucky to see day 11… so it varies by sensor…

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Have you ever tested the same finger drop of blood on same meter, using multiple strips? You will likely see the number vary 5-10 pts or more, based on brand and low vs high bg.

So when comparing meter to cgm, consider they are both approximations. After awhile you will get used to what is normal for your situation. For example, when I put dexcom in arm, my readings are closer to finger stick BG, compared to dexcom on my thigh. But it is really the trends and “ballpark” number that matter, not the precise digits.

I think everyone goes through this phase when first starting cgms. I started with the archaic medtronic Sof-sensor in 2008ish, the dexcom seven, G4, G6, so have experienced the transition in accuracy and usefulness over time.

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This article is a couple of years old, but just goes to show you how glucometers can vary in accuracy. Something to keep in mind when comparing meter vs CGM data.

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phew ! I made the cut. at Eric’s recommendation last year, I tossed my ONE TOUCH meters ( they were all awful ) and started on the Contour Next One meter. I’ve never looked back. I have 3 of them. one in my bag, one bedside, and one in my travel “D” bag.

I highly recommend it to all and Medicare pays for 300 strips per month ta boot.

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Agreed.

Agreed again. :hugs: