What is the acceptable difference between a FreeStyle Libre system reading and a blood glucose reading?

Blood glucose readings and interstitial fluid (ISF) glucose readings taken simultaneously won’t always match, and that is to be expected. There is a physiological delay in ISF glucose response to changes in blood glucose; the time lag is 2.4 ± 4.6 minutes for adults and 2.1 ± 5.0 minutes for pediatrics. This difference is similar to a train ride in which a “blood glucose car” is toward the front of a long train and an “ISF” car is toward the rear. Both cars will pass the same points along the way, but the “blood glucose car” does so minutes ahead of the “ISF car.”  Glucose readings based on ISF have been proven to reliably reflect glucose levels.1  For specific questions on making treatment decisions based on the Sensor glucose reading, the Glucose Trend Arrow, and Glucose Graph, please contact your health care professional.   


1. Alva S, Bailey T, Brazg R, et al. Accuracy of a 14-Day Factory-Calibrated Continuous Glucose Monitoring System With Advanced Algorithm in Pediatric and Adult Population With Diabetes. J Diabetes Sci Technol. 2022;16(1):70-77.

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