Does It Make a Difference Where You Put Your FreeStyle Libre Sensor?

Dear Dr. Edelman, I love the FreeStyle Libre, but sometimes when I put on a new sensor, the readings are higher than with the previous sensor, even if I didn’t eat anything. Is that normal? Does it make a difference where you put the sensor?

Dr. Edelman: The location on your arms should not matter that much. Wide swings in glucose when you swap out sensors is not uncommon at all, and a lot of folks going on CGM are surprised about that. All sensors can be inaccurate, but you should double check with your glucose meter (yes…prick your finger) to get a comparison. Remember you need to have very clean fingers before testing and there is a thing called the lag time in that if you are going up or down quickly, your finger stick value will lag behind. If you have a sensor that is way off, like over 20% from the finger stick value consistently, call the company to get a replacement sensor for free. Lastly, all sensors are less accurate the first 24 hours after putting on a new one.


Additional Resources:

How Do You Keep Your CGM In Place and Keep It from Irritating Your Skin?

Troubleshooting Tips for CGM Users

The World’s Smallest CGM Gets FDA Approval, and Bigger Isn’t Always Better!

Continuous Glucose Monitoring for Type 2s: An Incredible Tool to Take Control of Your Diabetes

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    In “Does it make a difference …” article.., Did he mean to say finger stick would lag or sensor glucose Would lag?

    • Hello…the sensor reading lags since it is not measuring blood like a finger stick does. Interstitial fluid is what sensors measure.

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        Hi. In this comment, you say “The sensor reading lags”. In the article, you say “Your finger stick value will lag”. They cannot both lag – one must lag, the other must lead. I think that “the sensor reading lags” and “the finger stick value will lead”.

        • Both the finger stick value and the CGM value may lag compared to the true circulating blood, because remember it takes time for blood that’s on your finger stick or in the sensor (interstitial fluid) to reflect the glucose level that’s truly circulating in your blood. But the finger stick helps you compare numbers to the CGM.

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      I was under the impression from my previous reading that the fingerstick will be the first reading, and the CGM will lag if blood glucose is going up or down quickly. Please confirm.

      • When the blood sugar is dropping, your true circulating glucose level will be lower than the CGM reading, and if your blood sugar is rising, your circulating glucose level will be higher than the CGM reading. That’s an important concept, especially when you’re dropping.

        • I work private duty for someone and when checking her senor monitor against her blood glucose finger stick the senor is always wayyyy, lower, and yet she also is on a sliding scale humalog with the results, which also makes me wonder if she even gets the accurate insulin amount.

          • Hi Margaret, CGMs can be off by as much as 15% in either direction, so if someone’s blood sugar is 200, the actual number could be anywhere between 170 – 230. You can keep finger sticking if you’re nervous about it.

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            This is what happened to my husband after open heart surgery. The readings were way off and he is on a sliding scale, how can he really tell the accurate insulin? we tried 3 sensors and all 3 did the same thing. I’m wondering if we should try again, now that he is 3 months post surgery? Will it make a difference?

            • Theoretically there should be no difference because glucose value is glucose value. There’s nothing he’s taking that could interfere with the accurate measurement. But Dexcom and Eversense are the most accurate.

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      Do you have to switch arms every 2 weeks or can you use the same àrm

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    3 of the last sensors fell off before 2 weeks? Is there a way to make them stay longer?

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      Hi David,
      Here’s an article with ideas that will hopefully help:

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      You can buy Hypafix transparent tape in a roll that covers the sensor and the roll lasts a long time. I bought mine at a medical supply store

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      I had the same problem I ordered a package of “SIMPATCH” pre-cut adhesive patches from Amazon. You can get them with or without a hole in the center. I recommend without the hole. It’s to hard to get on properly. I work in construction so Does it matter how much I sweat, swim shower it stays on with the same patch added to it and it doesn’t really affect being able to scan the sensor I’ve been using it now for about two years no problems whatsoever. I hope this helps

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      Don’t get it wet . Cover it while you shower if you can! Make sure you clean your arm good and use the alcohol pads

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      Using skin tac adhesive barrier wipes have really helped mine stay on! So much so that it takes some effort actually getting the sensor off when it’s expired!

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      We use Tegaderm Film (2.375×2.75) by 3M to cover the sense. It is waterproof and protects the sensor. Got them on Amazon.

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      I put a large waterproof bandage over it.

    • you can buy some sure stic from Amazon it helps sensor adhere

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      Call the company and give them the serial numbers and they will send you new free ones!
      Also go on Amazon and they make a clear adhesive cover to put over it. I use them it works. If you have a latex allergy they make ones latex free.

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      I haven’t read all the replies, so if this has previously been mentioned, my apology.
      After you remove the application device, rub your fingers (or it works better if someone else can do this for you) around the adhesive area a couple or three times, applying pressure as you this.
      When my cousin got her first one, she put it on & it didn’t stay on 24 hours. I helped her with the 2nd one & it stayed on very well. Hope this helps!

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      I put bandaid over mine it works really well

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      You can buy adhesive band-aid like covers designed to place over CGM sensors to keep them on.

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      I had the same problem. My doctor told me about skin tac. No problems since I started using it. Got it on amazon

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    I believe I have a helpful hint to help with the sensors being not accurate during the first day. During your last full day of your old sensor, keep it on but also attach a new sensor. The next day, remove your old sensor after it has expired and start the new one after putting the transmitter into the new one (if applicable). Since the new sensor has been on for a full day and the tissue has had time to recover from the insertion process, your new sensor should have accuracy right from the beginning.

    • Anita, really good idea. I am not sure if anyone has studied that, but it makes sense!

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      Echo the Dr.’s comment about your idea being a really good one. I’m getting a replacement sensor from the manufacturer as latest one is giving me readings that are way ‘out of range’ than the previous 8+ sensors I’ve used since being diagnosed. Usually as sensor is a lag indicator, there is a 30-40 point difference from a blood strip test done within 2-3 minutes of a sensor scan. Latest sensor is 70-90+ points different. I’ve been 95-100% in range for weeks, actually ~2 months, and in 2-3 days of new sensor have been hitting highs (230+) that I’ve never had before.

      I want to follow your suggestion when I get the replacement sensor – only issue being that the current one will still have 9 days left. Do you know if possible to start a new sensor before previous one has expired, and if yes, how? I’m guessing worse case, I attach new sensor for a day and then simply remove the old sensor and hopefully that will trigger Start New Senor when I attempt to scan the new sensor.

      Thanks in advance.

      • That’s a good question for the National Association of Off-Label Libre Users…haha. I’m not really sure if it works, but you can only use one sensor at a time if you only have one reader. The only way to have two going at a time is two have two readers.

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          Sorry I wasn’t clear. Not wishing to have two (2) active sensors at a time. I was following on from Anita’s good idea about how to potentially mitigate the wide swings in initial readings with a new sensor, i.e., in last day of currently active sensor, to attach new sensor BUT not start it until active sensor expires. Anita’s idea being that would allow time for tissue around new sensor insertion site to settle down and so hopefully the new sensor would be more accurate from the beginning.

          My issue was that in my case the current sensor will have quite a few days ‘life’ left but I don’t want to wait that long to activate the replacement sensor I expect to receive from the manufacturer tomorrow. So question was – do I simply remove existing (but unexpired) sensor after new sensor has been attached for one day – and then start new sensor.

          Anyway, I will report back as to what happens.

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            My experience with the Freestyle Libre is that I can remove a currently applied sensor no matter how many days it has left before expiring, simply apply a new one, then scan/read and start the new one. Of course, the message “wait one hour to begin” will appear after starting the new sensor.

            Often I have a applied a new sensor on the opposite arm about 12-24 hours before my current one has expired to allow it more time to be accurate from the start. DO NOT SCAN OR READ THIS ONE UNTIL THE OLD ONE EXPIRES. It does not matter that you have an inactive sensor applied in a different location. My experience is that WHEN I make the second one active by scan/reading it, the readings seem closer to the finger stick readings within the first hour, rather than 6 hours plus.

          • Got it – to answer your question, yes that’s fine.

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            Pleased to report back confirming what Anita and Diane have stated, i.e., attaching new sensor for 12-24 hours BEFORE starting it, has a noticeable (positive!) effect on how quickly the new sensor’s readings are closer to finger stick readings.

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    I put a new sensor on and it did the first part and said to wait a hour. When I went to take the first reading it said to replace the sensor. That it wasent working. Now im out a sensor. I haven’t taken it off yet. Was going to wait to talk to the pharmacist on monday.

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      Did you ever get this resolved? I’ve had 4 do this. I’m about to go back to finger sticks. Unfortunately I test 5-6 times a day.

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      call the 800 number on the box, that happened to me and they replaced and I sent the other one back at no cost to me

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      That happened to me and I got the same messages. When I finally gave up on the sensor and pulled it off, I saw that the sensor prick didn’t go into my skin and was bent, so the sensor was basically just taped to me. It was my first time and I didn’t plunge it correctly. Did you figure out what happened to yours?

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    The sensor breaks my arm out, and I don’t know why. Any one else experience this?

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    I am starting after several years getting irritation on my skin from the sensors.

    Can I put it on another part of my body like my stomach

  7. Do you have to put it in your arm or can you put in your stomach area

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      According to Abbott’s website, sensor placement is not approved for sites other than the back of the arm.

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    Has anyone experienced higher glucose readings when placing the sensor on different sides. When I place the sensor on my right side my readings are at their usual/normal level but when I place it on my left arm I get higher readings. Just wanted to ask if anyone else has experienced this?

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    Does anyone else have pain when they flex their arm? I have only had 2 sensors so far, and I did not have much pain on my left arm but I am experiencing pain on the right arm where the needle is. I am right handed. When I say “flex” I only mean that the tricep muscle is flexing because I am stretching or something similar, not weight lifting. Is there a better place on the back of the arm than others? It seems like the needle is so long that it is going into my muscle. Any help is appreciated.

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    I would prefer to not wear this on my arm. Is it still valid to wear elsewhere on the body? Abdomen for example.

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    Can you wear the sensor on the outside of your arm?

  12. Is it ok to wear my FreeStyle Libre 2 Sensor on my mastectomy side, where my sentinel lymph nodes were also removed?

    • I don’t know for sure, but most likely it will be fine and not an issue. If you do try it, do some finger sticks to confirm that the readings are close enough.

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    Is it OK to put my Libre sensor on the arm I sleep on? I’m a side sleeper,

    • Yes, but there is something called compression, and if you see your blood sugar drop out of the blue for no reason with no symptoms when you’re laying on the sensor, check your blood sugar with a meter. Sometimes that happens occasionally (it happens with the Dexcom too). If it does happen, don’t sleep on that arm as best you can. You can also put the sensor in other spots on your arm so your aren’t directly laying on it, like on the back of your arm.

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    Can I can I put my sensor on the same armEvery time

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    Can you put the sensor on the side of the arm instead of the back of the arm?

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    Is there any other locations on the body , other than arms you can place the sensors?

    • In reality you can put it anywhere on the body with subcutaneous tissue, but it’s only FDA approved for wear on the back of your upper arm.

    • Why would anyone listen to this guy telling you to put the sensor somewhere other than where the manufacturer and the FDA tell you to put it?

      • Hello Chris, thank you for your kind comment. It turns out that I do have well over several decades of experience using these devices (especially the Libre) along with thousands of my patients at the Veterans Hospital, UCSD Healthcare System, and TCOYD. You can put it anywhere you have subcutaneous tissue.

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        Just reading through some of these comments in the thread and gotta say, yours stood out for all the wrong reasons. What a disrespectful UNkind thing to say to Dr. Edelman. He does know what he’s talking about and his comment is valid. Dexcom is similar but opposite. It’s approved for wear on abdomen but people also wear it on their arm with great results. Have a NiCe day! ✌🏼

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        And we certainly believe EVERYTHING we get from the FDA! Like getting covid shots.

  17. I’ve been wearing my sensor on my thigh for about 6 weeks now, with my doctor’s approval. My readings have been accurate. I discontinued use of the device about 2 years ago because I hated that it showed during the summer. This is a much better solution for me.

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    I have just started using my free style first sensor didn’t make the 14 days they sent me a replacement sensor and now this one quit working it had 10 days left and it came lose. Is there any suggestions as to how to keep the sensor from coming loose

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    I have been wearing Libre 14 day for about 6-8 months and I love it, in the past week, I have had to replace my sensor 3 times as it ends abruptly and states to replace. This last one would not work at all. Has anyone had similar problem, am concerned to put on another as not sure if there is a problem with my arm or the sensor and they are very costly for me. I am getting replacements but have to wait for them to arrive. Has anyone had multiple sensors not work and is there something I can do to prevent.

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    My Libre 2 goes off all night saying it is low. 52 is the lowest. When I get up and stick my finger it will be over a hundred.. Anytime I use my reader and the check it by sticking my finger they are never close.. I’m not sure what to do. Someone said not to lay on it because it gets hot and miss reads. Is this true?

    • The FreeStyle Libre is notoriously inaccurate in the lower ranges, so what you’re experiencing is not abnormal. There is also something called “compression” that can happen to any device if you lay on it really hard – the blood sugars may look like they’re dropping like crazy.

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    Hi has anyone had any issues re sensor if put on your arm where there are lumps (from injecting)? This is my 3rd sensor that really doesnt like to work on my left arm and i am now thinking its maybe due to my injection sites? Any thoughts thankyou

    • Sounds like what you’re describing is lipohypertrophy from injecting insulin into the same site, and I would definitely put your sensor in a different spot, and inject in a different spot too.

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    What is an acceptable variance in the numbers in the Freestyle 2 versus finger sticking?

    • Hi Jocelyn,
      The national standards are to be within 20% of the true value, and the finger stick test doesn’t really qualify as the true value. When the CGM sensors were tested, they were tested against laboratory methods. For example, if the true blood sugar number is 200, what’s acceptable is anywhere between 160-240 (20% of 200 is 40). When blood sugar gets below 100, the difference should be within 10-15%. You have to control your expectations. The other thing to remember is, because these CGM devices are continuing to auto-calibrate, and because you get a new value every five minutes and you get a trend, having a number that’s not exactly perfect isn’t as detrimental as a single finger stick that is way off. If your hands are not perfectly clean and dry, or your strips have been exposed to air too much or are expired, the finger stick isn’t the gold standard. There was actually a study done where people touched different things like milk, sugar, water, etc, and a lot of things will give an abnormal finger stick value, so people get lulled into a false sense of security that finger stick values are gold.

      • Hello Dr. Edelman,
        I’ve been using the freestyle Libre 2 for about 7 months now but lately my arm has been itching around where the sensor is inserted while in my arm.
        Is there any suggestions on what to do to prevent this? Another time while the sensor was in for just 3 days, my arm got swollen so I had to remove it. When I removed it I noticed that my arm was infected. Is it possible that the sensor was bad? Because I always put in a new sensor after I take a shower and still clean my arm with the alcohol wipes before putting the sensor on.

  24. I am having a hard time I am a farmer killed my arms they got jerked off leg did not work can we place on the neck?

    • Yes…you can try you neck where there is subcutaneous tissue. I put my Omnipod on my upper back between my spine and scapula. You could also try the inside part of your upper arm. It’s currently only approved for placement on the back of the arm because that’s where it was studied, but you can put it anywhere on the body with subcutaneous tissue.

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    What about weightlifting? I do triceps extensions for example…
    And I don’t want my Libre to be visuable when I wear a T-shirt… So can I wear the Libre higher on my upperarm?

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    I removed my sensor ten days early for an mri. They couldn’t do the mri. My sensor parts are embedded in the arm. Just maybe one or three pieces. I’m being sent all around the hospital to try and find someone who is willing to try and remove it. Any suggestions for how it should be removed? The tape of the sensor is gone. The sensor plastic is removed. Just the filament pieces are in my arm.
    Please help any advice or future reference for what the protocol is. I still need to get an mri. I can feel that something is in my arm. And I can see one black spot

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      Hi Anna,
      We haven’t heard of this happening before. Hopefully the hospital has provided a solution by now, but we would suggest you also contact FreeStyle Libre customer support, explain the situation to them and see if can determine why the sensor parts would have remained in your arm. Here is their info:
      Good luck!

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    Hello Dr. Edelman and TCOYD, thank you for answering all these questions and also providing explanation where necessary. I have been learning quite a bit too from these posts and your responses. I am a PharmD and a diabetes educator. Thank you.

  28. Strange one this, but bear with me…

    Next month I’m appearing in a play at the Edinburgh Fringe. My character, the artist Paul Cezanne, removes his shirt half way for a massage.
    Conincidentally, Cezanne was himself a diabetic, but since the play is set in the year 1900 I don’t want the audience seeing the actor’s own Libre Sensor!

    I was hoping to monitor my glucose levels in the wings without the faff of finger pricking. Onstage hypos are not a pleasant experience!
    Would I be able to attach the sensor to the top of my THIGH instead of my upper arm? (I keep my trousers on, thankfully!)

    PS Red Rover Theatre Company’s ‘Visiting Cezanne’ by Duane Kelly is on every afternoon at the Hill St Theatre 5th-28th Aug. 😉

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      Hi Mark,
      Yes, you can wear the sensor anywhere you have subcutaneous tissue. Jeremy wears his Dexcom sensor on his thigh. Thanks for sharing about your play…that’s so cool! Wish we could fly over and see it!

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    Where can I put the sensor to keep blood from getting in it since I’m on blood thinner I have a problem with this

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    I have been making great efforts to get back on track to managing my Type 2 diabetes via diet plus exercise. My Libre 2 average glucose history has been 116/126/130/131 for last 7, 14, 30 and 90 days respectively. From all the conversion tables I’ve found, this should equate to <6.5 A1C. So you can understand my surprise and frustration when results from blood tests earlier this week reported A1C as being 7.2.

    Hoping someone can shed light on what maybe occurring or if had similar experience. Thanks

    • The lab is absolutely off. That’s within the range of possibility for laboratory error, which can be as high as .8%.

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    Should I switch arms when replacing a sensor with a new one?

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    My Libre gives different readings to my blood glucose monitor, dependent upon left or right arm application. Left arm is generally low by 1 mmol/L, Right arm is generally high by 1 mmol/L. Is there a more accurate placement area for the sensor and does it make a difference if you don’t have a lot of body fat?

    • In general, using the same body part on the right and the left should not give any differences. However, it’s possible that the arm reading might be different from the stomach during periods of exercise where your arm is generating movement and it has more blood flow to that area. Most people that contact us say there’s no difference in the different areas.

      It also should not make any difference if you have low body fat because the sensor is so small and thin and doesn’t go very deep. If you’re really skinny and you put it in an area where you have absolutely no body fat, it may cause irritation and pain because it will be hitting the muscle, and that might cause abnormal bleeding that could mess up your results.

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    Can I put a new monitor on the same arm that the old one was on but in a different location.
    My son had a vaccine shot and has a swollen arm so I didn’t want to use that arm if I can help it

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    Dr. E, I have been using a Freestyle Libre 14 for 3-4 years. After 8 to 10 days, maybe 12, they frequently tell me I’m low (50-ish) when I don’t feel low. When I do a finger stick (with a clean finger), the readings are frequently significantly higher than the FSL14’s “guaranteed within 35 points,” and almost always above the 20% you mention. A 50 reading and a 100 finger stick are not uncommon. Which do I trust–the FSL14 or the finger stick? I just reviewed your 2021 video on CGMs and read through all the comments above. You and Dr. P say in the video and above to trust the sensor, but throughout there are statements about checking with a finger stick when we have reason to think the CGM is inaccurate. I infer from those statements that I should trust the finger stick. I’ve been changing out the sensor when it starts reading so low, but am losing 1/4-1/3 of the life of the sensor and am paying out of pocket. I would try a Dexcom, but it’s unaffordable since it’s at least three times as expensive as the FSL14.

    • Hi Priscilla,
      First…the problem you are getting is a very common complaint, so you are not alone. Second…always do a fingerstick if your symptoms do not match the CGM value. Third…for sure call Abbott and they will send you a new sensor to replace the one that did not last two weeks and/or was not accurate.

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        I did this and it’s really hard getting the people to hear over in India. They don’t understand English. I had to call out the numbers slowly and say a word with each number. It took about an hour. I am hoping I get 2 sensors to replace the first 2 of my 6 in a bag at the pharmacy. I’m wondering if all the last ones were bad.

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    My sensor constantly says I’m having low blood sugars at 69 and going down. Pricked my and the finger prick says 111. Called the phone number to report my sensor not reading correctly and they gave me another to call and talk to someone about and still no response. It has been almost 14 days I guess no one wants to hear any complaints which I don’t blam them but these sensors are very costly out of pocket.

    • It’s well known that the Libre sensor can read inappropriately low, and if find that it continues to be way off, you should call their customer service back and talk to someone about replacing the sensor. And don’t take no for an answer! They generally are very good about that, and you may have not spoken to the right person.

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      I also had this happen. I’ve been scared to death. The first ones I got were good. These last ones seem bad. It’s falling to 50 at night when it’s normal all day. It’s scary!

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    I’ve been having problems with by sensor coming off. The back of the arm is not an ideal place for me as I find myself brushing up against things. I’ve been through two sensors in less than 10 days. I shower daily, so I am wondering if that is an issue with them coming loose?

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    Hi there, we get get my son’s Freestyle Libre 2 sensors through the mail. I know they’re not supposed to get over a certain temperature. They’re shipped in the regular mail so no special shipping. Could they get to hot in shipping and affect how they work? Thank you

    • It’s really not an issue for the sensors. If it was insulin, it’d be different.

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      exactly. Something has happened to the bag of 6 I just purchased. I have been freaked out by the low readings. It’s really not been good for my nerves. The first ones worked out so good. Are these being shipped from India? The man I talked to could barely understand English at all. It was painful spelling the numbers of the sensors . I don’t know if I’ll even get them or not. I am so disappointed. I’ve been panicked about the night readings. I wish I had only bought one, even though I am paying 35 out of pocket that’s 6 sensors so that’s 200+ dollars and my nerves are shot thinking I have severe low readings.

      • We’ve seen this problem with all sensors, and the best thing to do is make sure you have a glucose meter so you can double check.

  38. Why is it necessary to put the sensor where it’s going to show, and catch on things? I HATE IT. People are nosy, and I bloody hate their stupid, prying questions. Just as I hate having to wear long sleeves when it’s 80+ degrees outside to cover the damn thing up.

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      Hi Sandra,
      You can wear the sensor anywhere you have subcutaneous tissue. We know folks who wear them on their thighs, abdomen, etc.

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      I’ve been wearing mine on my chest, a few inches below my collarbone/around horizontal with my armpit, where it can sit under my bra strap (search it on You Tube). There was a learning curve to avoid where it is affected by movement, but once I figured that out it was so much easier! I don’t get compression sleeping, rip it off on clothing, hit it on doors, or worry about what to wear. 🙂

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