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People with Type 1 Diabetes Test Freestyle Libre Flash System Performance

Oct 15, 2019
Editor: David L. Joffe, BSPharm, CDE, FACA

Author: Keri Hames, PharmD Candidate, Florida A&M University, College of Pharmacy & Pharmaceutical Sciences

Can the Freestyle Libre Flash glucose monitoring system perform accurately when challenged?

In previous studies, the Freestyle Libre Flash was shown to improve glucose levels in the blood. However, these studies also showed that the system’s performance was impaired by high rates of glucose flux.  Researchers believe that there is a need to understand the extent of how the Freestyle Libre Flash works. The purpose of the study was to examine the glucose monitoring performance of the Freestyle Libre Flash when it came to certain tests.  These tests include high carbohydrate meals, disturbances in bolus-insulin, and physical exercise in patients with type 1 diabetes.

In this study, subjects had to attend four randomized trial visits.  These visits were 14 hours in length in an inpatient setting. During these visits, the subjects had alternating pre and post-exercise bolus insulin dose administration.  19 of the subjects were given three meals that were high in carbohydrates and were asked to perform moderate-intensity exercise sessions. Researchers compared venous blood glucose and capillary blood glucose, during exercise, to the patients’ interstitial glucose concentration.  The accuracy of the Freestyle Libre Flash was tested using Median Absolute Relative Difference (MARD), interquartile range (IQR)), and Bland-Altman and Clark Error Grid.  Researchers also used guidelines provided by integrated CGM approvals.

The overall result for the MARD (IQR) during the inpatient phases of the trial was 14.3% (6.9%–22.8%), during hypoglycemia (≤3.9 mmol/L) 31.6% (16.2%–46.8%), hyperglycemia (≥10 mmol/L)  9.4% (5.1%–15.7%), and euglycemia (4.0 mmol/L − 9.9 mmol/L) 16.0% (8.5%–24.0%). The MARD score for acute exercise was 29.8% (17.5%–39.8%), for hypoglycemia 45.1% (35.2%–51.1%), hyperglycemia 16.3% (10.0%–22.8%), and euglycemia 30.7% (18.7%–39.2%).  There was a bias that was shown with the Bland – Altman analysis (95% LoA) of 1.26 mmol/L (−1.67 to 4.19 mmol/L). 

The researchers concluded that the Freestyle Libre Flash was not adequately accurate when it came to patients being within the hypoglycemia range. The glucose monitor also had issues during acute physical exercise and had to have confirmatory blood glucose tests done along with it. Patients may feel that if they have to do back up tests with the Freestyle Libre, there may not be a point in using this device.  Also, we wouldn’t know when a patient is experiencing episodes of hypoglycemia. However, this study did have a limitation of having a small study population. 

Practice Pearls:

  • Previous studies showed that when continuous monitoring was performed there was system impairment when there were high levels of glucose within the blood.
  • The Freestyle Libre Flash has difficulties with accuracy when measuring hypoglycemia, acute physical exercise.
  • Confirmatory tests had to be done on patients to confirm that the monitoring was accurate. 


“Performance of the Freestyle Libre Flash Glucose Monitoring System in People With Type 1 Diabetes.” PracticeUpdate, https://www.practiceupdate.com/c/87193/1/8/?elsca1=emc_enews_expert-insight&elsca2=email&elsca3=practiceupdate_diab&elsca4=diabetes&elsca5=newsletter&rid=OTE0MTIxOTE4NTkS1&lid=10332481.

Moser, Othmar, et al. “Performance of the Freestyle Libre Flash Glucose Monitoring (Flash GM) System in Individuals with Type 1 Diabetes: A Secondary Outcome Analysis of a Randomized Crossover Trial – Moser – – Diabetes, Obesity, and Metabolism – Wiley Online Library.” Diabetes, Obesity and Metabolism, John Wiley & Sons, Ltd (10.1111), 5 Aug. 2019, https://onlinelibrary.wiley.com/doi/full/10.1111/dom.13835.

Keri Hames, PharmD Candidate, Florida A&M University, College of Pharmacy & Pharmaceutical Sciences