Flash Glucose Monitoring

Continuously measures glucose levels throughout the day

Designed to replace the need for routine finger pricks, a flash glucose monitoring system is made up of a sensor that is worn on the back of the upper arm that continuously measures the glucose concentration in the body's interstitial fluid. Using the FreeStyle Libre reader or the FreeStyle LibreLink mobile app you can scan your FreeStyle Libre sensor to see your glucose levels.


What's the difference between flash glucose monitoring and blood glucose monitoring?

Sensor glucose readings come from the interstitial fluid, a thin layer of fluid that surrounds the cells of the tissue below the skin4 and not from the blood.

Monitoring diagram

Watch the video to find out more about
 the difference between testing interstitial fluid vs blood glucose

Interstitial fluid readings and blood glucose readings don’t always match

Glucose in the blood takes time to make its way into the interstitial fluid so there may be a lag time. The average lag time between the FreeStyle Libre sensor and blood glucose readings is by about 2.1 minutes for children and about 2.4 minutes for adults8.

When glucose levels are stable, the two readings may be very similar. However, if glucose is rising or falling, then they might be different.6


When blood glucose levels are stable, the glucose measurement displayed by the FreeStyle Libre system in the interstitial fluid, are similar to blood glucose.


When blood glucose levels increase, the glucose measurement displayed by the FreeStyle Libre system in the interstitial fluid may be below the blood glucose reading.


When blood glucose levels decrease, the glucose measurement displayed by the FreeStyle Libre system in the interstitial fluid may be higher than the blood glucose reading.


The FreeStyle Libre System

The FreeStyle Libre system is the leading sensor glucose monitoring devices globally7 and the only flash glucose monitoring system in Ireland. They consist of a small, discreet sensor worn on the back of the upper arm with a FreeStyle Libre reader or phone app to scan the sensor. You must scan once every 8 hours for a complete glycaemic picture, ensuring you remain engaged with your glucose monitoring throughout the day.

How accurate is the FreeStyle Libre System?

The FreeStyle Libre system is accurate, stable and consistent over 14 days8 without the need for fingerprick calibrations.

To assess the accuracy of the FreeStyle Libre sensor, the glucose readings the sensor provides are compared to a known independent reference. In this case the reference is a finger prick blood glucose reading which is taken at the same time as the sensor scan. The comparison between the 2 different readings is plotted on a graph called a Consensus Error grid.

The closer the sensor reading to the reference blood glucose meter reading, the better the accuracy. This is reflected by the Consensus Error Grid by various areas on the graph labelled A to E. The higher the percentage of readings in Zones A and B, the more accurate the sensor is. The consensus Error Grid below shows 99.9% of readings in Zone A + B of the Consensus Error Grid in adults.5


All values vs Yellow Springs Instruments (YSI)


No finger prick calibration ever

Calibration is needed for commercially available CGM systems because the sensitivity of each sensor can vary within each batch that is made. The FreeStyle Libre flash glucose monitoring sensor is calibrated at the factory - so you won’t need to calibrate it using a finger prick, ever. This means you can be confident in the accuracy of the system, and you can be confident the accuracy you're receiving is what is reported, without being affected by discrepancies caused by finger prick calibration.

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