Endocrine Abstracts

Introduction: Recently, the factory calibrated FreeStyle Libre (FSL) flash glucose monitoring system has been introduced for use in patients with diabetes mellitus. We assessed the accuracy of FSL compared to the finger prick capillary blood glucose (CBG) over a 2 week period in patients with congenital hyperinsulinism (CHI) and assessed the parents’ experience of using FSL.

Methods: About 346 episodes of CBG along with corresponding swipe FSL readings were available form 7 children with CHI (0.4–5years). A detailed questionnaire was completed by the parents.

Results: The mean variation between the two methods was 0.55 mmol/l (SD ±0.9), higher readings by FSL compared to CBG. The FSL sensor stayed in-situ for an average period of 13.5 days. There was a positive correlation between the two methods (r=0.73). The FSL had a tendency to overestimate compared to CBG (bias=0.55 mmol/l; 95% CI: 0.46 to 0.65). Only 72% of values were within the reference standard (±0.83 mmol/l) at glucose concentrations less than 5.6 mmol/l. The overall Mean Absolute Relative Difference (MARD) was 18%. 31 episodes of hypoglycaemia (CBG<3.5mmol/l) were noted but FSL identified only 55% of these episodes. The Bland Altman plot showed the 95% limits of agreement between the 2 methods ranging from −1.23 (95%CI: −1.39 to −1.07) to 2.35 (95%CI: 2.18 to 2.51) mmol/l. Majority of the parents found the glucose trend on FSL to be useful to detect and prevent hypoglycaemic episodes. All parents felt that FSL is a very easy and convenient method to measure the glucose level especially during sleep. A significant proportion of parents felt that FSL readings were not accurate and 50% of parents expressed interest to continue using FSL after the trial period.

Conclusion: Noticeable variability between the two methods of measuring the glucose was noted. Despite the ease of using the FSL system, concerns related to accuracy, especially at low glucose values do remain although parents find the glucose trend to be very useful. Further larger trials are needed in CHI patients before FSL is recommended as a routine alternative method for measuring glucose values.