The Freestyle Libre 14-day flash glucose monitoring system is a continuous glucose monitor that measures interstitial glucose every minute and records it every 15 minutes. The Freestyle Libre sensor is approved for use by the FDA in human diabetic patients. Its use in veterinary patients is off-label. Interstitial glucose is the glucose concentration in the tissue/interstitial fluid, and it closely approximates the blood glucose, except at times when the blood glucose is changing rapidly e.g. after, meals, insulin administration, and exercise and then there is a lag between the interstitial glucose and the blood glucose.
The libre sensor is a small disc (size of 2 stacked quarters) with a soft flexible piece of tubing that lies under the skin. The sensor is placed on the neck, chest or rump. We clip a patch of hair, clean and dry the skin with alcohol, use a sticky wipe (skin tac wipe), then apply the sensor (painless), and sometimes use a dressing such as an adhesive patch or tissue glue, to help keep the sensor in place. If the sensor stays in place, it can measure glucose levels continuously for up to 14 days. It is important to be very careful not to displace the sensor e.g. do not use a collar if sensor is on the neck, avoid vigorous play, grooming, etc. The sensor can store up to 8 hours of data and must be scanned using the reader (or an app on your phone) at least once every 8 hours to capture all the glucose readings. The reader or app can store months of information.
The glucose levels are measured by scanning the sensor with the Freestyle Libre reader or the Librelink app on your phone. The sensor is ready to measure glucose 1 hour after it is inserted into the skin. During the 1 hour warm-up period, you can scan the sensor to see when it will be ready.
The sensor can be scanned using either a free app on your phone (Freestyle Librelink for iPhone 7 and up, or Androids running OS 5 or higher) or using a reader that can be purchased by prescription from your pharmacy.