Huge innacuracies

Hi folks, this is my first time on this site. I woke this morning with a FreeStyle Libre sensor reading of 2.2. So I had some glucose. Then I realized I should do a finger stick. The reading on that was 13.4.

I tested again with the meter and a finger stick and got 3.2 and 13.5!

I’m seriously not impressed. I have been seeing what I think are lower than usual readings, over the last while, but put it down to more exercise. Then I had an A1C reading that was 7.6! Way too high for the readings I have been getting, which should translate to something under 7.

Now I am away at a course and have 3 strips left and will have to get a cab and buy some strips so I can get anfrigging handle on what my levels really are. And miss the course I paid so much for.

I have no idea what to do next.
Has anyone had such huge innacuracies? And what did you do to address this? Would dearly love to hear your suggestions. Thanks.

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Welcome to the forum @Georgia_Barnwell!

CGM’s (whether they be Freestyle Libre or more costly Dexcom or Medtronic) are ~usually~ fairly accurate, however as you discovered this morning they have occasion to be out of whack. Often this occurs at night as the sensor is compressed and you’ve rolled over and slept on the arm or leg it’s affixed to (called a compression low).

Compression lows generally are only 1 or 2 mmol/L out, but I’ve had occasion to compensate (either with carbs or an insulin bolus) to false lows or highs. For the first year or so using CGM’s I’d never bolus without finger checking (have a meter on table beside the bed).

The best advice is to never be that far away from your meter, and know your body (most carb eating T1D’s will definitely feel confused and sluggish at 3.2 mmol/L). On the other end of the scale many of us feel just fine when BG is well above 10 or 15 mmol/L.

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Welcome to TuD, @Georgia_Barnwell. That’s frustrating. You mentioned that you treated a false low with glucose and then finger-checked and discovered you were actually high. My first question to you is: did you thoroughly wash and dry your hands before that fingerstick?

I’ve been bitten by that circumstance more than once. I’ve concluded that any high fingerstick reading that meant adding insulin to correct, I will always wash and dry my hands and re-check before adding correction insulin.

Our meters are generally accurate and dependable but they’re not perfect.

One thing I do every 90 days when I see my doctor and get an A1c check, is to get a lab plasma glucose check done and I do three fingerstick readings right after the lab draw. I average those three readings and compare to the lab number. That check, if the the lab and meter are reasonably close, confirms that meter/strips I’m using are accurate enough.

I don’t use a LIbre flash glucose monitor but I have read some accuracy complaints by online users. People overall seem generally happy with the system. It’s definitely less expensive than the Dexcom, the system I use.

Is it possible for you to switch to a Dexcom? I know there are people who use the less-expensive Libre since they have to pay out of pocket for this technology.

Have you called Abbott to see if it’s possible that you have some sensors from a bad lot?

Sorry for the frustration. When I travel, I try to bring with me 2-3x the supplies I expect to use to cover unexpected events. Diabetes seems to feature unexpected events. I hope you were able to get your strips without missing too much of the conference. Your immediate safety and health come first.

Please report back, especially if you can positively resolve your Libre/fingerstick disagreements. I highly recommend that you regularly check your meter against a lab. It’ll help you remain confident that your meter is giving you accurate readings. And failing to wash hands before fingersticking is a common source of inaccurate readings that often lead to incorrect treaments. Good luck!

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As usual, when I got up this morning my G5 reading was within 1 point of my Contour Next. Dexcom seems to work the best, of all the CGM’s. Consider switching?


Had the Libre and ditched it. Way too inaccurate for me. Went to Dexcom and the average is now off by 6% and this sensor is perfect as it’s average off off 4%. Libre was off 30%-50% and sometimes more.


Sounds like a bad sensor to me. I would call Abbott for a replacement. I don’t go anywhere without enough strips to get me through my day or trip in case a sensor malfunctions or falls off.

Technology in almost any form can fail in one way or another so I don’t blindly follow whatever it says. The Libre is an older technology and sometimes it will give inaccurate readings so if you can’t stand it then you should definitely switch to a newer CGM. The Libre is usually pretty accurate for me but I always make sure to finger stick before making a big BG related decision. If you can’t afford a different CGM then getting a Miaomiao to add on to the libre so you can calibrate the sensors will work really well.

Thanks Jim. The compression low makes sense, thanks. And I know I should have tested before using the glucose. What I have found though over the last couple of months is that the readings have been lower than expected during the day too, but just thought I had been getting more exercise. Will definitely check this out. Although I’m not sure what the point is of having to check on a sensor that should be accurate. Seems like another task in a day with too many already, lol. Anyhow, I am sure it can get worked out somehow.


Many thanks for this info, it will be helpful.

Hi, thanks for the info. I will check on the Dexcom. And I did wash handle prior to the finger stick. I have been tracking the sensor readings with finger stick all day and there is still quite a difference. I’d say at least 30%. I’ve only had it for 6 months, and knew that extreme highs and lows would be innacuracies but even midrange is way off. Appreciate your wisdom.

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Mine has been so accurate I dont remember to use strips anymore. Unless it’s really a questionable result. I agree with some of the advice given here. I do love my Libre.