Endocrine Society Advice on Insulin Dose Adjustment for Libre

Liam Davenport

November 27, 2018

Patients with diabetes who use Abbott's FreeStyle Libre continuous glucose monitoring (CGM) systems can now better manage their blood glucose levels with a new method for leveraging the trend arrows and precisely calculating the recommended insulin dose, say experts.

The guidance, published online on November 14 in the Journal of the Endocrine Society, focuses on two systems available in the United States: the FreeStyle Libre and FreeStyle Libre 14-day CGMs.

FreeStyle Libre received US Food and Drug Administration approval for use in adults with diabetes in September 2017. The FreeStyle Libre 14-day system, which was subsequently approved, has a longer wear time for the sensor and shorter warm-up period, which are comparable with systems available in Europe.

Yogish C. Kudva, MD, Division of Endocrinology and Metabolism, Mayo Clinic, Rochester, Minnesota, and colleagues were convened by the Endocrine Society to provide guidance on how to incorporate trend arrow information into insulin dose calculations for the Libre, as little had been provided.

"Our method fills the gap by suggesting strategies that healthcare providers and CGM users can use to refine insulin doses using trend arrows in the FreeStyle Libre CGM systems," Kudva said in a press release from the Endocrine Society. "We want to make it easier for CGM users to act on the trend arrow information."

The recommendations follow similar guidance issued last year on using trend arrow information with the Dexcom G5 CGM system to simplify the safe adjustment of rapid-acting insulin doses.

Patients With Diabetes Not Achieving Glycemic Goals

"A large proportion of individuals with diabetes treated with intensive insulin therapy are not achieving their glycemic goals and hypoglycemia remains a key obstacle to effective diabetes management," Kudva and colleagues write.

Underlining that the guidance is "intended to provide a safe, practical approach" to the use of CGM systems and trend arrows, they say that their method "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."

In addition to the two FreeStyle Libre devices assessed for the current guidance, Abbott's FreeStyle Libre 2 CGM was recently granted a CE Mark for use in European Union countries. This latest system is equipped with optional real-time alarms for high and low glucose levels that can be customized by the user or switched off if unwanted, but the latter are lacking in the two Libre systems currently available in the United States.

To develop guidance on using trend arrow data for FreeStyle Libre and FreeStyle Libre 14-day CGM systems, the Endocrine Society adopted a similar approach to that used for the Dexcom G5, albeit tailored to take into account differences between the systems.

As well as not having automatic alarms, the Libre systems available in the United States don't have the double-up or double-down trend arrows present on the Dexcom CGM.

Guidance Developed by Expert Users of CGMs

The Society convened an expert panel, which based its guidance on their clinical and personal experiences of diabetes and using CGMs, as well as guidance from other diabetes specialists.

The authors focus on patients with diabetes on multiple daily injections of intensive insulin therapy rather than continuous subcutaneous insulin infusion administered by a pump, as "these individuals currently make up a greater proportion of type 1 diabetes and type 2 diabetes populations on intensive insulin therapy."

However, they note that the recommendations are applicable to both treatment methods.

"Additionally, our approach is based on the anticipated changes in individuals using rapid-acting insulin analogs for prandial and correction insulin doses," the authors note.

For the Dexcom G5, the authors based their advice on a review of four previously published methods to adjust insulin doses using trend arrows.

This time, they modified the methods to reflect the features and functionalities of the FreeStyle Libre systems.

Comfort With Complexities of CGM Before Adjusting Using Trend Arrows

The authors nevertheless emphasize that, before starting to adjust insulin doses using trend arrows, patients should "wait until they are comfortable with the general application of CGM data and learn how their body responds to various meals and physical activity."

This, they note, is because "adjusting insulin dose using trend arrows adds a layer of complexity," and "the approach relies on the accurate determination of insulin-to-carbohydrate ratio and correction factors as insulin dose parameters."

This information is used to calculate the rapid-acting insulin dose, with insulin added or subtracted depending on the direction and angle of the trend arrow.

As for Dexcom G5, the adjustment recommendations for the Libre are based on typical sensitivity ranges, which are divided into four categories of correction factors: < 25, or very insulin resistant; 25-50; 50-75; and ≥ 75, or very insulin sensitive.

These categories determine how many units are added or subtracted from the insulin, in the range of -3.5 units to +3.5 units.

For example, a 44-year-old man with type 2 diabetes on continuous subcutaneous insulin therapy is about to eat a meal with 45 g of carbohydrate. He sees that his sensor glucose value is 164 mg/dL and an angled-up trend arrow is displayed on his device.

The meal requires 4.5 units of insulin and he has a correction factor of 1.1 units. With the trend arrows indicating that, based on his insulin sensitivity, a further 1.5 units should be added, the total dose would be 7.1 insulin units.

Unlike Dexcom G5, the FreeStyle Libre systems are not currently approved for pediatric use in the United States, and so no insulin sensitivity categories are given for such patients.

However, the authors set out a number of potential scenarios, including for postmeal monitoring and treatment, planning for aerobic exercise, sick day management, and management in frail individuals.

Above all, they emphasize the importance of patient engagement.

The authors write, "Optimal use of the FreeStyle Libre systems requires that patients and clinicians become actively engaged with utilizing CGM data in both real-time decision-making and retrospective analysis."

They conclude that "CGM has the potential to transform diabetes management."

Their approach provides a starting point for addressing "the needs of clinicians and the growing number of patients using CGM seeking an approach to safely reduce glycemic variability using trend arrow data."

The work was supported by an unrestricted educational grant to the Endocrine Society from Abbott Diabetes Care. Kudva has reported receiving research support from Dexcom, Roche Diabetes Care, and Tandem Diabetes. Disclosures for the other authors are listed in the article.

J Endocrin Soc. 2018;2:1320-1337. Full text

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