AskNadia: Is The FreeStyle Libre CGM Sensor As Accurate as Finger Pricking Blood Glucose Monitors?

Dear Nadia:

I have had type-2 diabetes for more than ten years.  I was first enthusiastic about lancing to see my blood sugar levels, but this dropped off.  My doctor checked blood fasting levels about every three months.  Then, she retired. My new doctor is a proponent of A1C testing over lancing.  
I recently was referred to an endocrinologist who put me on the Abbott FreeStyle Libre sensor and monitoring system.  It seems to track my blood sugar 24 hours.  When I pass the monitor over the arm sensor, I get the current reading and lines indicating whether the sugar level has changed between readings.
What is your view of the FreeStyle Libre system?  Is it as accurate as lancing?

Dear TW:

I liked reading that you started testing your blood sugar after being diagnosed with type 2 diabetes. Even though your healthcare professionals have different recommendations, they seem to be clear about one thing, testing your blood sugar is essential.

Testing your glucose levels also teaches you which foods shoot up your blood sugar and which foods make it easier to stay in a healthy range, helping you meet your A1c targets as determined by you and your healthcare professional.

Prolonged high blood sugars can cause complications. Monitoring and staying within your A1C goal can enhance your lifespan. Staying motivated in managing your blood sugar is not always easy. The important thing is to never give up on yourself by finding new solutions to a new problem.

It appears that the CGM technology has become the solution for you since you stopped testing your blood sugar. The convenience of the FreeStyle Libre CGM can help you achieve better blood sugar levels with a visual alert, bringing your attention to a high or low blood sugar trend, allowing for corrections to be made.

Self-Monitoring Blood Glucose (SMBG) Meter Accuracy

When glucose meters were introduced in the 1970’s, it was meant to help insulin-using diabetics. Initially, the medical community did not embrace the new technology for two reasons; they were concerned about the accuracy of the device and if patients knew what to do with the information.

The downside to finger blood glucose testing is that when you test your blood sugar, the reading is a reflection of where you are at that moment in time. You have no idea which way your blood sugar is trending. Is it in fact on its way up? or down? Knowing which way your blood sugar is trending can help you make a better decision when it comes to blood sugar self-management.

Feeling burned out from finger pricking glucose testing can cause your enthusiasm to drop. Some people who don’t test their glucose think that they can guess their blood sugar reading. One study proves otherwise. It is estimated that 46% of type 2’s who guess their blood sugar level, are inaccurate.

Having a device that reads your blood sugar is essential to your overall health. How else would you know how to correct a blood sugar unless you have biofeedback?

The Benefits to Continuous Glucose Monitoring (CGM)

CGM devices are the new darlings in diabetes blood glucose market. The allure of not having to prick your finger, wearing a sensor from 10 to 90 days depending on which device you use, is attractive to many. Especially, to the type, 2’s who are not using insulin.

I recently had a family member diagnosed with type 2 diabetes. Similar to your new doctor, their physician also recommended a CGM to them.

I believe we will see more and more of this; CGM’s replacing finger pricking for people who do not take insulin.

The FreeStyle Libre CGM

The Abbott FreeStyle Libre CGM sensor last 14 days, replacing the standard finger blood glucose test. The FDA approved the sensor for use on the upper arm. After two weeks the sensor needs to be changed.

It is the least expensive alternative on the market with a built-in glucose finger testing meter to check your CGM reading.

The one downside to the Libre device? Unlike its competitors, it does not currently have an audio hypoglycemia or hyperglycemia alarm to alert you when your blood sugar is falling or rising. You visually need to check your sensor and your blood glucose with a finger-pricking test to verify your reading. Having the CGM & BGM built in one medical device makes it easier to test without having to reach for another gadget.

It is just a matter of time before Abbott adds the alarm feature, making their CGM sensor even more competitive than just being the lowest cost CGM alternative in the market today.

The accuracy for the CGM sensor is the same as the blood glucose meter; it falls within a 20% plus or minus variance as set by the Organization for Standardization (ISO). Translation? The CGM can read 20% higher or lower than what the CGM reads. For example, if your sensor reading shows a 100-blood glucose reading, the 20% variance means your blood sugar can range between  80 and a 120 Mg d/L.

Today you have four different CGM devices to choose from; The FreeStyle Libre from Abbott Diabetes, The Dexcom 6 CGM, Medtronic’s Guardian Connect, and the new Eversense 90-day implantable continuous glucose monitor.

Both the self-monitoring blood glucose meters and the continuous glucose monitoring system are regulated by the International Organization for Standardization (ISO) where the 20% rule measures the device accuracy against laboratory test results. When in doubt, check your BGM & CGM medical devices tests immediately after your lab visit to compare the results.

Journal of Diabetes Science and Technology conducted an accuracy study on the FreeStyle Libra alarms. It was found that the hypoglycemia alarm still needs to be verified with a finger blood glucose test while the hyperglycemia alarm was more consistent.

If you would like to know the difference between the four CGM’s, next month, look online for our CGM chart comparison.


The Rationale for Continuous Glucose Monitoring-based Diabetes Treatment Decisions and Non-adjunctive Continuous Glucose Monitoring Use

Testing Versus Guessing Blood Glucose Values 

Alarm Characterization for Continuous Glucose Monitor That Replaces Traditional Blood Glucose Monitoring


Nadia’s feedback on your question is in no way intended to initiate or replace your healthcare professional’s therapy or advice. Please check in with your medical team to discuss your diabetes management concerns.

AskNadia and receive her unique perspective on your question.

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AskNadia (ranked #1 by Google), named “Best Diabetes Blog for 2017 by Healthline and with 24 nominations, Nadia Al-Samarrie’s efforts have made her stand out as a pioneer and leading patient advocate in the diabetes community.

Nadia was not only born into a family with diabetes but also married into one. She was propelled at a young age into “caretaker mode,” and with her knowledge of the scarcity of resources, support, and understanding for people with diabetes, co-founded Diabetes Interview, now Diabetes Health magazine.

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10 thoughts on “AskNadia: Is The FreeStyle Libre CGM Sensor As Accurate as Finger Pricking Blood Glucose Monitors?

  • November 5, 2018 at 5:45 pm

    I appreciate reading the information in your blog reading.

  • September 14, 2019 at 7:30 pm

    Your answer that the Freestyle is as accurate as a regular meter +/- 20% is no answer. Some newer meters are closer to +/- 10 % . I find that the Freestyle reads consistently 20 to 30 points lower than my meter and two others available to me. If I were to use only the Freestyle I might expect a1c’s under 6. For anyone expecting to stop finger sticking they might be disappointed. While I expect the usual disclaimer that everyone’s experience is different , I remain underwhelmed and will continue to finger stick. No one seems willing to criticize the Freestyle Libre system , and I find this also odd.

    • November 25, 2019 at 12:18 am

      For me it is atleast 20 points higher than lancing. And I may have done atleast 100 tests by simultaneously lancing and checking on the Freestyle libre over last 14 days. So in my case, I am trying to control my sugar based on Freestyle libre, the benefit I hope will be , I will be able to keep my sugar levels below the levels I see with lancing. But then I heard Lancing versus lab results will vary too. Lets hope for the best. Atleast we have some tools.

    • June 10, 2020 at 4:50 pm

      I found same thing freestyle libre. Readings are too low compare to finger pricking. I used freestyle without finger pricking and my doctor change my medication because it was showing very low. Now I am comparing my libre readings with finger pricking and differences is unacceptable. Yesterday my fasting reading was very low on libre and it could not read. After pricking my reading was 5.9. This morning after breakfast my reading with libre was 8.8, with finger pricking reading was 12.3
      This sensor will expiring in few days and that’s it and not going to use it anymore.

    • September 26, 2020 at 7:53 pm

      I have found that my Contour finger-stick glucometer readings are consistently 20% higher than my Freestyle Libre reading except for very low Freestyle Libre readings which may be 40% or more lower than the glucometer readings. I am very sensitive to feeling the effect of a blood sugar less than 70mg/dL, so when I get a Freestyle of LO or 40-60 and am feeling fine I know my true blood sugar is generally about 80-90. For readings above 80 or so I simply multiply by 1.2 and that comes very close to my glucometer reading. I have never had a Freestyle Libre reading that is lower that a same-time glucometer reading.

  • October 31, 2019 at 6:58 pm

    My wife uses the libre and altho its nice to see if blood glucose is steady…rising or lowering…there is a 60 to 100 points difference between libre and fingerpricks. Libre reads lower which is dangerous when basing your insulin injections on readings.

  • November 18, 2019 at 3:15 pm

    I recently started using the FreeStyle for my hypoglycemia. I know that my blood glucose runs low, but it seems that the CGM is recording it even lower! I have consistently been in the 40s or the scan reads LO, which I don’t think is quite accurate. I did a finger prick this morning after using it and it was at 87 while the other was at 40. Why such discrepancies? I am having a hard time trusting the CGM when my levels are at a consistent 40. I have looked and looked trying to determine if this is normal to have the numbers so far apart but all I can find is that the CGM is within 20% of accuracy which would mean that my blood glucose is between 32 and 48. Any thoughts or suggestions?

  • February 28, 2020 at 4:30 am

    Trying the Libre 14 day CGM, after 7 days of 30+ reading lower than blood testing. It was constant 30 points which was odd. I found that its accuracy was off enough that I stop it. Now after talk to Nurse I found out lot of patients had the same issues as I did. My doctor put the first sensor on me so it was installed correctly. Oh did learn that you can’t take aspirin, Vitamin C, or Tylenol and other thing medicals that will effect results. This is just me personnel experience yours might be different.

  • April 19, 2020 at 8:08 pm

    I have the new FreeStyle Libre 14 Day. Abbott has already replaced 2 of my first four sensors due to inaccuracy. The FreeStyle reads lower than the finger stick. With one sensor, the average deviation was greater than 25% and one reading was 42% lower! It has been reported that as many as 25% of FreeStyle sensors are “bad” (inaccurate). This is probably true because my Diabetes device supply house said Abbott was having trouble with sensors (they get the complaints) and Abbott will replace sensors for free, no questions asked. My finger stick meters have a precision of about +-10%. +-20% would make it difficult for proper insulin dosing. As of now, I am calibrating (comparing) my sensors to finger sticks. For now, don’t assume you won’t need finger sticks for proper insulin dosing.

  • January 1, 2021 at 5:20 pm

    My Libre readings are typically 10-20 points higher than pricking with a keto-mojo device.


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