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Discrepancy with CGM and finger pricking

  • 1.  Discrepancy with CGM and finger pricking

    Posted 23-04-2022 08:02
    The latest Libre CGM sensor that I am using is giving very unreliable readings. For instance it showed a LO and since I felt OK I checked with a finger prick and received a reading of 5.4. This is happening for most readings. The readings using the sensor are about 4 - 5 units lower than the finger prick. Are others having a similar problem? I believe the Libre2 is more reliable. After purchasing a new phone I tried to get the Libre2 through the NDSS as I had been able to for the Libre but to my astonishment I had to go through all the paper work before I could get the Libre2. Hopefully it will be more reliable once I am able to get one.

  • 2.  RE: Discrepancy with CGM and finger pricking

    Posted 24-04-2022 09:44
    I had trouble with the Libre2 Reader - I was awakened at 1am 2am 3am to say that I was under 4.    A fingerprick showed 6.1.  After talking with the Pharmacist, I was advised to contact Abbot which I did, and they asked me to check settings etc.  The Abbot person who answered my call asked me to check the settings etc and guided me through (I have only been using this for about 18 months) and we found nearly all the areas showed an error.  Thankfully, Abbot expressed a replacement reader and they also included a box for me to return the faulty one.  I have also contacted them about the sensors falling off my arm and they replaced that one as well.  The Pharmacist advised that if I come in and get more sensors, I could use up the entitlement too soon,  and that I should contact Abbot  about this issue.   When I have an appointment with my Endo,  a check is made of the sensor situated on my arm, and is quite happy with the placements.


  • 3.  RE: Discrepancy with CGM and finger pricking

    Posted 25-04-2022 10:12
    Hi Margaret
    i have been using L2 for about 4 months, overall it works very well with the smart phone app, just some times when i can feel a low coming on the lag time for app might be a few minutes late to show this below 4.1 where it is set as low. Recommend L2, L1  was hopeless.


  • 4.  RE: Discrepancy with CGM and finger pricking

    Posted 24-04-2022 10:27
    Hi Marion

    I've been using Dexcom G6 for a couple of years and it is very accurate. Before that I used Libre (before Libre 2 was invented) and I had a lot of issues with inaccurate readings - a difference of around 5 units like you. I eventually discovered that there  were probably 2 reasons for this - not drinking enough water and taking vitamin C supplements. In the fine print of the paperwork that comes with the sensor it mentions all the things that can affect the accuracy of the readings, so it's worth checking out. I don't know if this is still an issue with the Libre sensors but it seems likely.


  • 5.  RE: Discrepancy with CGM and finger pricking

    Posted 24-04-2022 15:15
    Hi Marion, I made enquiries at the pharmacy about the Libre2 reader and was given paper work to fill out. As I'm already registered with NDSS I contacted them and was told that if you are  registered you would receive an email after April 27 to advice that the sensors would be available after that date but to contact Abbott about the reader. They advised me  if I was already registered with NDSS as a concessional person I would have to contact them after May 1st and they would arrange for a new Libra 2 reader FOC. You need to give them your NDSS membership number. I f I wanted those items sooner I would have to complete the application through my D. Educator or endocrinologist.
    I hope that helps.


  • 6.  RE: Discrepancy with CGM and finger pricking

    Posted 24-04-2022 17:04
    Just to let you know, the libre 2 is very accurate,  so much better than libre 1, I use to put next libre 1 on 24 hrs before activating to stabilise it, no need with 2, except have found can get  a dud  sometimes,   says check in 10 min abs then may end up saying sensor fail. I ring Abbott, and they replace for free, just post free back the dud. Example of good readings checked my level with blood test was 4.1 yesterday,  read sensor, same 4.1. 
    Rarely test with blood meter. 


  • 7.  RE: Discrepancy with CGM and finger pricking

    Posted 25-04-2022 13:30
    This thread is very interesting to me as I had the same experience with Libre 1. When contacting abbot I felt that it was only me with the problem. It was "very unusual" to have such discrepancies. It was difficult to get satisfaction- a solution for the next sensor or a replacement. I eventually gave up on it as it was costing me a fortune- $92 for a fortnight for random readings! I have found G3 Medtronic cgm accurate and reliable. There was a flier in my transmitter box that warned about the use of Panadol - not compatible with sensor.


  • 8.  RE: Discrepancy with CGM and finger pricking

    Posted 26-04-2022 10:33
    Hi T1's with discrepancies. The Libre2 is great, what you must realise is that the reading is
     not as immediate as finger pricking, you must set your L2 so that you get your low warning before it becomes urgent (knowing that it will).
    Your finger prick will give you your blood sugar level on the spot.
    Your L2 will give you your level. Because you are not testing blood directly, the result will be a little slow, hence setting your low warnings a bit higher. (You know, give you a little more time)

  • 9.  RE: Discrepancy with CGM and finger pricking

    Posted 26-04-2022 14:33
    Hi John,

    I realise the delay using sensors as they use interstitial fluid not blood. I commented on the libre 1 which gave readings of 3 when bloods were 10! And I also (on advice from ADE) tested bloods with a 15min gap with similar, huge discrepancies. They were not "a little" out as I was expecting and happy to accept. 

    The Medtronic guardian sensor however,has been accurate and within range. 

    My diabetes educator didn't believe the libre's difference in readings to the finger prick until she saw the difference herself. Then we tried a new one with her inserting it to see it if was user error. It wasn't. The sensor was out often and by a lot so was of no use to me. Just a very expensive exercise while I kept persisting. 

    The Medtronic has a finger prick for calibration 3 times a day and the readings are generally closely aligned - except when glucose is rising or dropping quickly as you'd expect. 

  • 10.  RE: Discrepancy with CGM and finger pricking

    Posted 27-04-2022 07:30
    Hi all, I used Libre 1 and now use Libre 2. I connect it to an IPhone, when I start the sensor, which gives me all the alarms. I am the same as John, because it reads fluids not blood, I set the alarms to give me time to take glucose or food when it is low or take insulin if it’s going high. I also have the reader and I check with a blood prick if am at all worried.
    Regards Joan

    Sent from my iPad

  • 11.  RE: Discrepancy with CGM and finger pricking

    Posted 26-04-2022 10:44
    on reading all of these comments it makes me very glad that I just use the ole finger prick. simple quick and good readings. If I feel unhappy I have about 4 other testers to compare.


  • 12.  RE: Discrepancy with CGM and finger pricking

    Posted 27-04-2022 13:50

    Now that CGM is being subsidised and accessible to more people I would encourage people to consider it and talk to their endocrinologist/diabetes educator about it. Finger pricks are like taking a photo of glucose control - it gives a picture at the time of taking the photo only. CGM is like cctv - it gives the entire picture 24/7. It also gives you the insulin profile with food, activity, trending and what is going on while you are sleeping - finger pricks don't give this information.

    It also generates reports from the data and can give you a percentage of time in range figure and a glucose management indicator (close to Hbac1) every fortnight instead of waiting 3 months for the Hbac1. Endocrinologists and diabetes educators now use CGM data in their consults and say Hbac1 is becoming redundant because it's an average and doesn't give the picture of what is going on. Someone can be fluctuating between big highs and big lows and still have a good Hbac1.

    The research has been done and has concluded glucose control and diabetic outcomes improve with CGM because it has enabled more precise and accurate insulin dosing leading to more stable glucose levels. Ophthalmologists say damage to eyes is caused by spikes in glucose which are picked up by CGM ( and rectified) not Hbac1's or fingerpricking

    I have hypo unawareness and CGM has literally saved my life and given my life back to me. Yes there are deviations in readings and technology glitches but the benefits of CGM outweigh these greatly. The research outcomes show this and I don't think you would find an endocrinologist on the planet who would disagree.

    I hope this gives a more positive outlook about the benefits of CGM. To anyone in doubt I would suggest talking to your health care team. Technology and medical research are greatly improving peoples lives and health but it requires a person to be open minded and agreeable to change for benefits to be reaped.


  • 13.  RE: Discrepancy with CGM and finger pricking

    Posted 29-04-2022 08:18
    Kim, I totally agree with all that you wrote about CGM. They have saved me trips to the Hospital and many call out of Ambulance. I feel much safer during the night knowing that the CGM will warn me in plenty of time if going LOW. I have no natural warning about HYPOS,  lost that many years ago so I love my CGM.


  • 14.  RE: Discrepancy with CGM and finger pricking

    Posted 30-04-2022 09:29
    Spot on Kim!


  • 15.  RE: Discrepancy with CGM and finger pricking

    Posted 01-05-2022 15:35
    Thanks Kim (and Anita and Michele). A terrific summary of the security and comfort one feels with the CGM and its range of graphical reports. My Libre 1 tells me I consistently swipe it for a reading 17 times a day - not that I'm consciously timing myself - but it seems to be a suitable frequency to stay in front of the 'worm' to keep that Hbac1 where it should be all the time.

    I am unsure about the CGM "warning" that users speak about. I assume it is an audible warning. If so, I've never heard it, as I'm pretty short of hearing. This remains a worry at night. Must read the instructions!