Department of Pharmaceutical Care, University of Iowa Hospitals & Clinics, Iowa City (Dr. Schleich); Department of Family Medicine, Carver College of Medicine, University of Iowa, Iowa City (Drs. Schleich and Ray) kevin-schleich@uiowa.edu
The authors reported no potential conflict of interest relevant to this article.
Two isCGM systems are available: the FreeStyle Libre 14 day and the FreeStyle Libre 2(both from Abbott).a Both consist of a reader and a disposable sensor, applied to the back of the arm, that is worn for 14 days. If the patient has a compatible smartphone or other smart device, the reader can be replaced by the smart device with the downloaded FreeStyle Libre or FreeStyle Libre 2 app.
To activate a new sensor, the patient applies the sensor, then scans it. Once activated, scanning the sensor provides the current glucose reading and recalls the last 8 hours of data. In addition to providing an instantaneous glucose reading, the display also provides a trend arrow indicating the direction and degree to which the glucose level is changing (TABLE 110,14,15). This feature helps patients avoid hypoglycemic episodes by allowing them to preemptively correct if the arrow indicates a rapidly declining glucose level.
Continuous glucose monitor readings often vary slightly from venipuncture or fingerstick glucose readings.
For the first 12 hours after a new sensor is activated, and when a glucose reading is < 70 mg/dL, patients should be instructed to avoid making treatment decisions and encouraged to utilize fingerstick glucose readings. FreeStyle Libre 14 day does not allow a glucose level alarm to be set; the system cannot detect these events without scanning the sensor.10 Bluetooth connectivity does allow FreeStyle Libre 2 users to set a glucose alarm if the reader or smart device is within 20 feet of the sensor. A default alarm is set to activate at 70 mg/dL (“low”) and 240 mg/dL (“high”); low and high alarm settings are also customizable. Because both FreeStyle Libre devices store 8 hours of data, patients must scan the sensor every 8 hours for a comprehensive glycemic report.14
FreeStyle Libre CGMs allow patients to add therapy notes, including time and amount of insulin administered and carbohydrates ingested. Readers for both devices function as a glucometer that is compatible with Abbott FreeStyle Precision Neo test strips.
Real-time CGMs(rtCGMs) measure and display glucose levels continuously for the duration of the life of the sensor, without the need to scan. Three rtCGM systems are available: Dexcom G6, Medtronic Guardian 3, and Senseonics Eversense E3.
