Freestyle Libre - Coping with inaccuracies


First time post, long time reader.

I got the Freestyle Libre system and after using it a few weeks, I can only say the disappointment is like a wet blanket on my hopes.

The first sensor I installed caused bleeding - a lot. The readings the next day were all over the place. Abbott Labs (USA) said I probably bent the needle when I installed it (ha), but in the end, they sent me a replacement sensor. Okay, that’s good of them.

The second sensor I installed - right next to the placement of the first - resulted in no bleeding, no issues. The next day, finger sticks revealed it was reasonably accurate, 15 minute delay and all. I was really really happy with it. Like a kid with a new toy, I was taking 50 to 60 readings a day and happy as can be. Occasional finger sticks confirmed it was reasonably accurate with discrete measurements and in trends. Wooooo.

After ten days, I took it off and put on a third sensor. Blood. Argh. The next day the readings were 40 to 50 mg/dl off. The amount of variance was not consistent over time or by the level of the reading. Abbott Labs (USA) said I must have installed it wrong (ha) but in the end they replaced the sensor. After some conversation, they sent me a coupon for a substantial discount on further sensors (I have no insurance).

Fourth sensor showed no blood. Next day, it was 40 to 50 mg/dl off. Argh^2. Waves of depression waft over me. I licked my wounds by coming to this forum and reading the experience of many similarly afflicted. As a result, I installed the Glimp app on my phone and a glimmer of hope shines on the horizon. Many finger sticks later, Glimp calibrates and estimates a more accurate translation of the sensor readings. Strange to relate, the variance between BG (from two different glucometers) and the Libre sensor varies as time goes on. It was rather big yesterday, 18 hours after installation, and now (almost 36 hours after installation), the variance is small. I also think the variance is different if my levels are low versus high. In other words, I think the variance is non-linear. I think it is geometric.

I would like the kind readers to read these statements and tell me more about them, especially if they are not true:

  1. The little metal sensor (the Probe) 5mmx0.4mm must hit the interstitial fluid found in the subcutaneous layer of your skin;
  2. The probe must not strike a blood vessel, be buried in a fat cell, or extend into muscules to take accurate readings;
  3. The majority of the length of the probe must be in that fluid. If half of the probe is in fat and the other half in fluid, the readings won’t be as accurate;
  4. Everyone’s skin is different, and is a different thickness on different areas of the upper arm;
  5. The variability in the accuracy of the sensor is a function of how much of that probe is marinating in interstitial fluid and how much of the probe is stuck in fat, muscle, or marinating in a capillary;

–> I’m wondering how I can select a place that does not have blood vessels and does not have an inordinate amount of fatty tissue. Would transilluminating the skin with red or white light reveal a better spot than another?

–> Does anyone have experience hitting a blood vessel? Can you carry on with the sensor or must it be replaced?

–> Does anyone have an opinion about Glimp’s ability to “calibrate” the readings?

I can’t thank you enough for reading and responding. I really got tired of finger sticks and honestly wasn’t doing it as much as I should. If I can find a way to get reasonably accurate readings from this FreeStyle Libre device, or at least a reliable trend, that would be a terrific positive thing in my life.

Thanks again!


I have no experience with the Libre but nine years of using a Dexcom CGM. For me, when I see widely variable glucose readings, I often later observe blood at the site. Whenever I see blood, I always swap out the sensor at the first opportunity. I’ve read accounts of people getting dependable service even with blood present but that’s not been true for me.

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Been using the system since March, arm only and I am very thin. My readings have been amazingly the same or close to my Roche meter readings. I have seen maybe some old small amounts of dried blood, but never hit a vessel. From the people I know who have, they say they pretty much leave it on unless there is a gusher.
I dont have anymore technical answers, but that has been my experience.

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I had a “gusher” on the first Libre sensor I used and it gave me a quarter sized bruise but the sensor was accurate after about 24 hours so I wouldn’t personally take out a bleeder. The Libre is well known to be inaccurate for the first 24 hours so I always put my new sensor on the day before my current sensor is going to end. I use the Spike app with an add on to the Libre that sends the readings to my phone and I really recommend it because I don’t have to deal with any off readings when I do get a wonky sensor.

Try moving around where you put the sensor on your arm. I find the most accurate ones are when I get it as high up as possible on the underside of my arm (like right beyond my armpit). I can’t put the sensor exactly where it is recommended because I’ve got a lot of scar tissue on the back of my arms from decades of injections and it hurts to insert it and for several days afterward (accuracy is fine though).

Hydrate, the more water you have in your body the more interstitial fluid the sensor has to work with. I have both quite a bit of fat and muscle on my arms so I don’t really think that is an important factor in accuracy but if you are very thin it might not be as comfortable to wear (I would think).


The first thing that I wish to point out is that some sensors just DO NOT WORK very well. If it is way off, they will replace it, if it is within their margin of error then you are out of luck. I have found that using glimp, where you can actually calibrate with some testing done via some other source, you can actually make more sense of the reading of your sensor.

I have been using the libre for a year and a half, always on my arms, and I find that when I put the sensor on the bottom top edge of my arm, as my hand is up is where I have the least amount of pain and good results.

I do not have much fat, and use my arms muscles while I do sports.

I have noticed that usually, if a sensor hurts, it wont give great readings, I can not make theories on a sample so small as mine is…

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I have been using Libre since last Christmas with the xdrip+ app (Xdrip+ is for android and Spike is IOS).

Never had a bleeder and never had much pain. The only really bad sensor I have had was when I tried it on my stomach. I place mine on the front of my arms - my biceps.

Having used about 40 sensors over 18 months G5 and Libre I now know that they vary. My last 3 Libres had 2 reading 15% high and one about 10% low on average. with a range either side of this average of up to 15%. Occasionally you get a rogue reading out side of this but not often.

One of the advantages of adding a transmitter and open source app is of course that you can calibrate it. Also in the States it will then run for 14 days. As mentioned above it is best to put it on 24 hours ahead. It will still run for the 10 days in the States and 14 days elsewhere.

I have a BMI of about 23.5 and never felt that sensor wire was not in right place.

There have been many discussions on the fb pages and forums as to where is the best place for the sensor and the thigh is mentioned a bit and one show off claimed the ankle is the best place! I find the back of the arm inconvenient because of putting on my transmitter and the danger of then knocking it off in doorways.

If you want to find out more about Libre plus transmitters read the article “All about CGM” on my website .

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My experience with the Libre system is new and limited. While I LOVE getting the graph, the many readings with just a swipe, my first two sensors gave me readings lower than a meter blood reading, evening allowing for the time lag between blood and interstitial fluid. When I applied my 3rd sensor, I started the 12 hour warm-up and after waiting 12 hours for a reading, I got an error, saying I needed to replace the sensor. WHAT ?!?!?!

Not only was that my LAST sensor as insurance will not allow your refill until you are already using the 3rd sensor, but I had just struggled 12 hours earlier to remove the 2nd sensor that had completed, but now I was going to have to pull off another sensor in just a mere 12 hours. That was just too much pulling off sensors in too short of a time for me. I was so very disappointed.

I called Abbott and they replaced the sensor and I returned the “dud” to them.

I find removing the sensors a royal pain so I took a break from using the system for about 2 weeks. I was afraid of another placement and then removal just 12 hours later if it did not work.

While I love the system, the verdict is still out on its reliability. I hope the “dud” was the oddity and not indicative of future use. I would like to know WHY it did not work. Was it, as you indicated, maybe too near blood vessel, embedded in fat cells, or was it just a bad sensor? Finding a place on my arms that is not filled with fat cells could be problematic for me. :slight_smile:

Getting ready to place my 3rd sensor. Break time is over. Back to the obsession with my new toy. It is hard not to over use it when it is new. So easy to take a swipe. Love that part.

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I find your response very helpful and reassuring. My fourth sensor varies a different amount from blood sugar, even minutes apart, and Glimp is showing how inconsistent it it. I’m beginning to think it is a bad sensor. On the bright side, I’m back to ten to fifteen finger sticks a day to keep Glimp calibrated :slight_smile:

I really appreciated your input. Are you still attempting to use the Libre system? I am just about to give up on it. I started a new thread tonight regarding my love/hate relationship with the system. I hope you will find time to read it and comment.

PS. I don’t have a “smart phone” so using Glimp is not an option for me. I don’t even have a laptop. No wi-fi or anything involving modern technology. I am lucky to use a desktop computer and find this forum. :neutral_face:

Glimp is useless - calibration or not

I share your pain. I used two models of MM sensors–for more than 12 months, in total. What a drain on my patience. They were random-number generators, as I used to refer to both systems. Now life is good–I’ve been using a G5 for 13 months. I’ve had either one or maybe two sensors that I removed before 7 days in that time. All the rest have gone 7 or more days and quite accurately.

I’m late to the party so apologies if this is covered up-thread, but my experience with bloody insertions is that they go haywire the first 24 hours but are generally fine after that. I have had to bail on a flakey sensor only once in 5 years using Dexcoms–just recently as a matter of fact–but there was no blood, just the first actual faulty sensor I’ve ever had. Dunno if Libre behaves anything like the same, but I’d at least give it a day before deciding it’s no-go.

Yes, I never quit on any sensor on the first day, regardless of model. (unless it fails to initialize, of course)

I have been using the Freestyle Libre system since mid 2018 and no problems until recently. I’ve noticed the new sensor I put on a few days ago has readings that are about 30 to 40 points higher than my actual blood sugar. It has never been off more than 5 points prior to this. The sensor has a delay in regards to how many days left. This is weird and I am assuming it is either a problem with the sensor or the meter itself is beginning to have a malfunction. I have friend who also uses the Freestyle Libre and he told me had to scan the sensor three or four times to get a reading and it sometimes wouldn’t scan through his shirt. Apparently, it was a meter issue.

Call Abbott/freestyle libre customer service. If it is a meter issue they can probably diagnose it over the phone and they might send you a new one depending on how long ago you got the system.

I have now gone through a 3 month supply of sensors. To say I am disappointed in the results is an understatement. I think there is a scalar error in these devices meaning the higher your sugar is the worse the error. I have had issues with blood glucose devices as well. 3 different meter measured within 5 minutes all the sites in close proximity to each other and reading varying by as much as 100 points. Not happy when I use these devices to determine how much insulin to take. I decided not to spend anymore of my own money on these sensors, since they are not very good.

I have been using Freestyle Libre for just over three months and I love it.
I really don’t care that a sensor is offset from my meter. I just look at my graph from the night before between 2 and 4 am Which for me at least is always very flat.
That becomes my target for the rest of the day. If one sensor gives me a target of 70 and the next gives me a target of 90 or whatever I just go with it. This has worked well for me as my A1c went from 7.3 to 6.2 after 3 months. Of course the reports generated by Libre view are garbage but again I just don’t care.

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I have been using FreeStyle Libre for approx. 2 months. No bleeds and worn on the back of my arms as indicated on the instructions.
I had Roux en y Gastric Bypass to help with my diabetes about 8 years ago. Recent studies have shown some patients are developing reactive-low glucose many years post operation. This is a versu serious condition which has recently been acknowledged in the field. The reactive hypoglycaemia is identified in some by eating a carb then the patients own insulin kicks in and basically doesn’t settle down sending the patients glucose too low.
My experience with the Libre is that I have been getting frequently very low readings. These low readings are happening daily and sometimes lasting hours while I am sleeping. Unaware, I see the alarming readings in the morning. One was 2.5 mmol (anything below a reading of 4 is considered low). I was freightened by my consistently low readings. I called customer support at Freestyle and was quite concerned when I learned from the Freestyle Customer Support person said that the diabetic society allows for an error margin of 20%. When readings are so low a 20% variable renders the meter useless. They sent me some test strips to compare my readings for future measurements. The representative said that the Libre is not recommended for low readings and to use the test strips.
My Bariatric doctor is now aware of the inaccuracies of FreeStyle Libre and one of the nurses who is non diabetic is monitoring her sugars and getting low sugars on the Libre. The claim of not needing to use test strips is misleading by Freestyle Libre.
The stress that I went through believing my sugars were so low then hearing customer service tell me that it’s potentially within the 20% of veriability was discerning.
I also contacted Dexcom and discovered they are the only sensor system approved to use as a tool to administer insulin by.
I’m afraid I am very dissatisfied with the Libre and will opt for Dexcom for my personal situation. Hopefully my insurance will cover it as well.
Good Luck to all of you…

I wrote a comparison of the Libre and the Dexcom under the heading Choosing a CGM. I wore both sensors for about 3 days when I first switched.

I have worn a Libre for a year and have recently switched to Dexcom.

But what I would do with the Libre is test a few times the first day so I could tell how far off it was, if it was more than 30 points or it was variable sometimes higher, sometimes lower, I would call and get a replacement. I could also get a replacement through Walgreens where I purchased them by telling them it was too far off. I also liked to start my new sensor before the older one ran out as then it helped make an easy comparison the first day, (I had 2 readers). I found the Libre was always off, but it usually stayed off by the same amount. There are aps that you can download on your phone to get alarms. But I did recently switch to the Dexcom as it is supposed to be more accurate and already has alarms.

I’m still not completely sold on the Dexcom as I’ve had problems with the adhesive staying on and while I can calibrate the Dexcom I have found myself finger sticking more than I did with the Libre. But it is very new to me so I haven’t learned to trust the numbers yet. It did take a few sensors on the Libre to start trusting it too.

I’ve used the libre for about a year now with no problems, however I recently had a bad sensor that they replaced, same thing with the blood vessel… I tried the outer thigh, which is not approved, but with the bad sensor, the arm placement didn’t work because it didn’t heal properly, and I was able to use it for 14 days using the xdrip+ app, which also allows calibrations, but the arm is much less problematic. I was always concerned with seat belts, and nothing in my pockets, etc. On the thigh, I would use my abdomen, however that’s Where the majority of my insulin shots are. I have always used the xdrip app and the blucon NightRider for alarms, however after having the bad sensor, I thought I might have a bad blucon and bought the miao miao with the arm band holder which is much better. I’m surprised no one has mentioned these… it turns the libre into a real cgm with customizable alarms and everything… my libre is usually spot on as long as its not during a recent meal or insulin shot… calibrartions should be done during fasting periods according to my endocrinologist. Which makes sense