For a week or so I’ve been getting wildly inaccurate low readings from my Freestyle Libre, especially at night. For example, at 4 a.m. the sensor swiped at 50, but a finger stick put me at 127. Tried a sensor change and it’s still happening. T1D was just starting to feel a little manageable after 4 months! 
@Lmolmen hi Lisa, I am sorry if someone said that CGM were perfect or completely accurate, Even the best sensors today are not completely accurate, because they do not measure blood sugar directly, the CGM measures a characteristic in “interstitial fluid” which is supposed to approximate actual blood sugar.
Some people find the errors are so great, that the CGM loses much of it’s value as a single solution. Others find that it’s “OK” but you need to back it up with a finger stick when you are unsure. And finally some people find it very accurate and use the CGM values as actual blood sugar and they are fine.
If you find the CGM versus finger stick OK during the day, then it may be useful for you to continue.
I would say if your sensor is close to a site you already used, you may have to rotate CGM sites more. If you are a little dehydrated, you may also find the results may vary. Some people get larger errors when they “sleep” on the sensor site.
in my opinion, I am not overjoyed with any CGM system, It’s a tool, and the numbers have to be checked because of inherent inaccuracy. when it’s working right, it can be helpful.
Hi. Mom of 15-yr old T1D (March 2017 diag).
I hope it is ok for me to post here. Being a parent. For what it’s worth, daughter has Dexcom G6 (was G5) and we are finding it very accurate. FOR HER. And we all know, everyone is different! But, it has been rough with roller coaster numbers the last several months and the nighttime lows have gone down so fast, we thought it was wrong. Has been on target when tested.
Take care.
I’ve been using a G5 with the xDrip+ Android app (love it!) and have found there is an art to readings, especially when there is a lot of “noise” in the readings (high standard deviation)
- You need to figure out what your ‘max drop is’. What I mean by that is what is the most you’ve dropped in a given time, verified by an actual test.
- You need to understand the circumstances that caused the above steep drop: how much insulin, circumstances (alcohol, exercise, Rx, etc.)
- When your CGM goes wacky and shows a drop that doesn’t make sense you need to put #1 and #2 in context and judge.
If the drop doesn’t make sense, I might just roll over and go back to sleep.
If it seems possible, test yourself.
No CGM is 100% and that’s incredibly frustrating. Adding your own intelligence can make a big improvement with your device.
Best of luck
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Thanks, Joe and Tami, very much appreciate both your responses!
Whoops, and thank you, too, Tim! I just read your reply.
The Freestyle Libre is notorious for false lows.
Hi Lisa, I used the Freestyle Libre for a while but found the readings very different from a finger stick. Once the sensor said Lo and on finger stick I was 141. While I was getting fasting labs drawn the sensor said 51 but my glucose was 32, The only advantages are the ease of use or no finger sticks and the trending arrow. Abbott didn’t have any answers and just said that they were sorry and thanks for being a loyal customer. My A1c went up 0.6 probably because of me eating to cover lows when I wasn’t that low. I went back to finger sticks.
Thanks, Paul. Were your readings consistently off? Mine have been accurate most of the time, especially during the day, and then get wonky at night. This started happening rather suddenly, after a few months on the Libre.
I had just started taking baby aspirin and discontinued magnesium and potassium supplements when I began to see these odd readings. Just for a test, I started back on the magnesium. A few days in, it looks like they’re improving…time will tell!
Thanks for your reply.
Hi Lisa, I use the Libre also. Make sure you are rotating arms every 14 days, and if you take any Vit C supplements they will get
greatly affect your readings. If you did swing low at night, the reading will take longer to show your blood sugar rise being interstitial fluid, verses a blood finger stick. Hopefully the sensor is inserted correctly too. Hope this helps!
Hi Lisa, The Libre readings were lower than my meter 99% of the time and would be as little as 10mg% or well over 100mg%. I don’t think magnesium or potassium will alter your readings. Good luck!