In the era of telehealth amidst the COVID pandemic and a time when technology is becoming more integrated into patient care, continuous glucose monitoring (CGM) systems are becoming more integral in diabetes management. CGMs have been shown to reduce A1C, reduce hypoglycemic episodes, reduce nocturnal hypoglycemia, increase treatment satisfaction, and increase therapeutic time in range.1
Pharmacists can help identify patients who might qualify for CGM, assist patients and providers with selecting the most appropriate device, provide counseling to patients on CGM, and interpret CGM result data. In order to better understand CGM management, it is best to begin with understanding CGM-specific vocabulary as defined below.
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Term
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Definition
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Calibration
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Requires a person to check glucose with a traditional glucometer and enter that number into the CGM receiver, which helps to ensure device performance and accuracy
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Warm-up time
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The period after installation of the CGM device in which glucose can’t be read
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Sensor
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The part of the CGM with the filament that is worn by patient
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Transmitter
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Some CGMs require this, some don’t. This is worn by patient on top of the sensor
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Receiver
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Can either be a handheld device or a mobile app. This is the monitor in which patients can see their glucose readings
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Ambulatory Glucose Monitoring (AGP)
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One-page summary of glucose readings interpreted by healthcare professional
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Personal CGM
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CGM owned by patient
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Professional CGM
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CGM owned by provider/clinic; only used by patient temporarily
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Traditional blood glucose monitoring coupled with regular A1C testing do not provide information regarding patient’s day-to-day variabilities in blood glucose. Continuous glucose monitoring can provide up to 288 glucose readings per day, providing a more complete picture of fluctuations in patients glucose readings. There are two broad categories of CGM devices: personal and professional. Below is some information on the FreeStyle Libre (14 day and 2) and Dexcom G6 as these are the most common personal CGMs seen in ambulatory care pharmacy practice. The FreeStyle Libre 2 was approved by the FDA on June 15, 2020 and differs from the FreeStyle Libre 14 in that it can be used in patients as young as four years old (rather than 18 years old) and has the addition of high/low glucose alarms. It is worth noting that a mobile app has not been approved with the use of the FreeStyle Libre 2, whereas, one can be used with the FreeStyle Libre 14 Day. The Dexcom G6 replaced the Dexcom G5 which is no longer in production.
Historically, in order for a patient’s CGM supplies to be covered by Medicare, a patient must be insulin dependent (regardless of type of diabetes) requiring injections three or more times per day or having an insulin pump, require at least four self-monitored blood glucose (SMBG) measurements per day, and require frequent insulin adjustments based on SMBG measurements. However, with the recent pandemic, more patients have been approved outside of these coverage parameters. Medicaid and private insurance coverage will vary from state to state and from plan to plan.
Information regarding patient education, product ordering, and data interpretation can be found on each products’ respective website. Local drug representatives could also provide insight into state-specific coverage.
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Feature
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FreeStyle Libre 14 Day2
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FreeStyle Libre 22
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Dexcom G63
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Minimum age for use (years)
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≥18
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≥4
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≥2
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Sensor wear time, days
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14
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14
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10
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Required calibration with SMBG
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No
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No
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No
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Optional calibration with SMBG
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No
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No
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Yes
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Warm-up period
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1 hr
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1 hr
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2 hrs
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Alarm warnings?
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No
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Yes (if within 20 ft of reading device)
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Yes (if within 20 ft of reading device)
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Drug interference
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Ascorbic acid >500 mg/d can lead to false increase in readings (dose dependent effect)
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Hydroxyurea (unstated dose) can lead to false increase in readings
APAP >1,000 mg Q6h is contraindicated: can lead to false increase in readings
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Salicylic acid >650 mg can lead to false decrease in readings
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n/a
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FDA approved for insulin dosing?
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Yes (except for the 1st 12 hours of wear)
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Yes (except for the 1st 12 hours of wear)
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Yes
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Approved sites
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Upper arm
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Upper arm
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Abdomen (all ages), upper buttocks (2-17 y/o)
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Counseling Points2,3
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FreeStyle Libre 14 Day
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FreeStyle Libre 2
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Dexcom G6
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Must hold receiver to sensor to scan every 8 hours or else there will be data lapses
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Water resistant up to 8 feet for 24 hours
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Scanning can be done through clothing, just hold within 1.5 inches of sensor
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If further than 20 feet of the receiver, there may be data lapses
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Water resistant up to 3 feet for 30 min
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Counseling points for all CGMs
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· Make sure skin is clean and dry and clear of any cream or lotion before inserting the sensor (to ensure adhesiveness)
· CGMs are contraindicated with MRI, CT scans, or diathermy: remove prior to these procedures
· CGMs are safe in metal detectors but are likely to set them off; recommend notifying airport security of CGM sensor
· All CGM devices can be used while showering, bathing, swimming (preferable to avoid hot tubs, saunas)
· Always check SMBG if the way you feel doesn’t match how the CGM reads
· Severe dehydration and water loss can cause inaccurate readings
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References:
- American Diabetes Association. 7. Diabetes Technology: Standards of Medical Care in Diabetes-2020. Diabetes Care. 2020;43(Suppl 1):S77-S88. doi:10.2337/dc20-S007
- FreeStyle Libre System Providers: Personal and Professional CGM. https://provider.myfreestyle.com/. Published 2020. Accessed December 16, 2020.
- Proven. Protective. https://provider.dexcom.com/. Published 2020. Accessed December 16, 2020.
- Isaacs D. The pharmacist’s role in continuous glucose monitoring. Pharmacy Today. 2020 May. Available at: https://www.pharmacytoday.org/action/showPdf?pii=S1042-0991%2820%2930344-3.
- Cornell S. Implementing Continuous Glucose Monitoring in Pharmacy Practice: The Evolving Diabetes Landscape. Pharmacy Times Continuing Education. 2020 Feb 14. Available at: https://www.pharmacytimes.org/resource-center/optimizing-diabetes-care-with-cgm.
Article written by: Lauren Speakman, PharmD, PGY2 Ambulatory Care University of Illinois at Chicago
Article reviewed by: Rachel Murdock, PharmD, BCACP