Trending: New Guidelines on Using Flash CGMs

Glucose monitoring systems can provide information on trends in glucose levels that can be a key in making dosing decisions. Specific to the newest entry, the Endocrine Society has issued a usage guide to make life easier for both clinicians and patients.   

 

High-tech options for diabetes management continue to proliferate so quickly that it can be difficult to keep up. The U.S. Food and Drug Administration approved Abbott’s FreeStyle Libre flash glucose monitoring system late in 2017 — and the Endocrine Society has responded with new guidance for providers and patients on how to make the most of its feature of providing trend arrows to alert users to which way their glucose levels are headed.

In 2017 the Endocrine Society published a similar guidance for the first “trend arrow” continuous glucose monitoring (CGM) on the market, the Dexcom G5. Dexcom soon followed that model up with an even more advanced model, the G6, which requires no calibration by the user through fingersticks.

The FreeStyle Libre system comes in two versions, one designed for use over 10 days and one over 14 days, with neither system requiring calibration by the user.

The Libre differs from the Dexcom models in that the Dexcoms communicate with a reader device (including a cell phone) with no patient intervention, whereas the Libre requires the patient to scan a reader over the sensor — hence it is often referred to as a “flash” glucose monitoring system. The Libre systems also do not have the automatic alarms that are built into the Dexcom models.

The important feature that the two systems share is that in addition to glucose readings, they display trend arrows that alert users about whether their glucose levels are holding steady or heading up or down.

Meeting the Need for Education

“There are more and more CGM options available, but there is a lack of educational materials for both patients and providers on how to use them” says Yogish Kudva, MD, of the Mayo-Clinic Rochester, Minn., who chaired the panel that wrote the document. “This is the second initiative from the Endocrine Society to provide more educational material. [This expert panel built on the experience of the previous panel] by developing patient educational material in parallel with the provider document.”

For providers, “Approach to Using Trend Arrows in the Freestyle Libre Flash Glucose Monitoring System in Adults” was published in the December print edition of the Journal of the Endocrine Society, and for patients, the Society developed a webpage about CGM systems in general and a downloadable brochure specific to the Libre: hormone.org/cgm.

“There are more and more CGM options available, but there is a lack of educational materials for both patients and providers on how to use them. This is the second initiative from the Endocrine Society to provide more educational material. [This expert panel built on the experience of the previous panel] by developing patient educational material in parallel with the provider document.” – Yogish Kudva, MD, Mayo Clinic, Rochester, Minn.; Chair, Guideline writing panel

Impact of Trend Information

These new systems are affecting treatment by showing the importance of putting glucose readings into the context of which way the level is headed, says L. Kurt Midyett, of St. Luke’s Hospital of Kansas City and a member of the guidance-writing committee. For example, glucose readings of 180 mg/dL can result in different actions, depending on the context. “If you put [the numbers] into the context of directionality, they are dramatically different. [You would take different actions] if you had a blood sugar of 180 that was rising very rapidly versus a blood sugar of 180 that was falling very rapidly versus a blood sugar of 180 that was very stable and flat. The number itself becomes immaterial. It is the movement that we want to try to focus on. Someone might actually give themselves insulin if the blood sugar was rising very rapidly [and do the opposite if it were falling] to try to prevent a low blood sugar. Yet the number is exactly the same, “ Midyett says.

The information from a few fingersticks in a day provided only a snapshot of a patient’s status, and “we couldn’t figure out why a patient might have a completely opposite reaction to the same treatment,” says Midyett. The information on how the patient’s glucose was trending helps explain the diverse reactions.

Expert Opinion

Trending information is still so new that there is not a published evidence base for decision-making, so the new guidance is based on the expert opinion from clinicians who have experience with patients using CGM systems. Hence, it is titled an  “approach” instead of a guideline. But this lack of a formal evidence base could make the recommendations all the more important for clinicians who do not deal with the new technology every day and could use help in getting up to speed. The expert panel’s work was supported by an unrestricted educational grant to the Endocrine Society from the Libre’s manufacturer, Abbott Diabetes Care.

“Our goal is to provide guidance that facilitates individualized recommendations for trend arrow use and data assessment. Our approach focuses on typical insulin sensitivity ranges used in adults and provides a range of adjustments in discrete insulin units. We believe this simplified approach reduces numeracy requirements and the number of calculations, which will help patients improve glucose control and increase glucose time in range without hypoglycemia, while promoting clinical discussion.” – from “Approach to Using Trend Arrows in the Freestyle Libre Flash Glucose Monitoring System in Adults”

Developing recommendations on how to use the trend information is made more difficult by the fact that the Dexcom and Libre display different arrow combinations — the Dexcom has seven combinations compared with the Libre’s five. (The Dexcom includes “double up” and “double down” arrows that the Libre does not.) Midyett said that the guidance-writing process drove home to him “the importance of developing a universal language of glucose management with more uniformity in nomenclature.”

Tips on Exercise

Kudva says that one area in particular in which the Libre expert panel could add information that was absent from the Dexcom guidance “was about physical activity and exercise and how patients could use the CGM signal to manage their glucose.” The guidance and the patient brochure both contain tables with recommendations. For example, in the case of a “pre-exercise glucose concentration” of 100–180 mg/dL, it gives the general advice to “exercise carefully; rescan every 30 minutes to avoid hypoglycemia.” Specific advice relating to the trend arrow is: If the arrow is pointing straight up or 45 degrees up, “rescan in 30 minutes.” If the arrow is stable or pointing 45 degrees downward, “consider ingesting 15 g carbohydrate.” If the arrow is pointing straight down, “consider ingesting 30 g carbohydrate.”

“Our recommendations are intended to provide a safe, practical approach to using the FreeStyle Libre systems, in general, and trend arrows, in particular,” the guidance document concludes. “Our goal is to provide guidance that facilitates individualized recommendations for trend arrow use and data assessment. Our approach focuses on typical insulin sensitivity ranges used in adults and provides a range of adjustments in discrete insulin units. We believe this simplified approach reduces numeracy requirements and the number of calculations, which will help patients improve glucose control and increase glucose time in range without hypoglycemia, while promoting clinical discussion.”

— Seaborg is a freelance writer based in Charlottesville, Va. He wrote about the Endocrine Society’s new clinical practice guideline on treating adult survivors of childhood cancers in the December 2018 issue.

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