The Endocrine Society has published new guidance for how to incorporate trend-arrow information from the Dexcom G5 continuous glucose monitoring (CGM) system into insulin dose adjustments for patients with diabetes.
The two documents — one each for adult and pediatric diabetes patients — were published November 20, 2017 in the open-access Journal of the Endocrine Society.
Grazia Aleppo, MD, of the Feinberg School of Medicine, Northwestern University, Chicago, Illinois, was the lead author of the adult paper, and Lori M Laffel, MD, MPH, of the Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, was first author on the pediatric guidelines.
"We know CGM offers the opportunity to increase glucose time-in-range without severe hypoglycemia. Now, we can further optimize glycemic control by using CGM trend arrows to fine-tune insulin doses," Dr Laffel told Medscape Medical News.
"CGM provides glucose information that is more than just a static number. The CGM trend arrows give an understanding of which direction the glucose is going and the speed of the rise or fall, allowing one to make dose adjustments in anticipation of the rising or falling glucose level," she added.
The recommendations are geared toward patients who use CGM with either insulin pumps or multiple daily insulin injections.
However, they apply only to the Dexcom G5 system, which was approved in December 2016 by the US Food and Drug Administration for "nonadjunctive" insulin dosing, thereby eliminating the need for confirmatory finger-stick blood glucose testing in calculating insulin doses.
Recently the FDA approved another nonadjunctive glucose monitor, the Freestyle Libre, but it works differently and is not currently approved for pediatric use in US but in EU from 4 years old.
"Fine-Tuning" of Dose Adjustments Accounting for Insulin Sensitivity
Four previous papers have addressed the incorporation of CGM trend arrows in the calculation of insulin doses along with the actual current blood glucose level, anticipated carbohydrate consumption, exercise, and other factors. But each of those methods "has various limitations in its complexity, utility, and applicability," the authors write.
Rather than require the patient to calculate a percentage or to alter the actual glucose reading, the new method advises increasing or decreasing the insulin dose in units based on the patient's insulin sensitivity.
Those who are more insulin sensitive will need less insulin to make the trend adjustment, and vice versa. "Percentages are hard for patients. It's much easier to recommend adjustments by units," Dr Laffel observed.
The sensitivity is denoted by the patient's previously determined correction factor (ie, the amount in mg/dL that the patient's glucose level will drop per unit of insulin).
For adults, there are four categories of insulin sensitivities (or correction doses): <25 (ie, very insulin resistant), 25–50, 50–75, and ≥75 (very insulin sensitive). Five insulin sensitivity categories are given for pediatric patients: <25 (eg, an insulin-resistant teenager), 25–50, 50–75, 75–125, and ≥125 (eg, an insulin-sensitive toddler).
Charts in the documents provide guidance on the amount of insulin to add to or subtract from the usual dose of insulin that would be given to cover carbohydrate intake or to correct an elevated glucose level. These dose changes are based on the trend arrows according to the patient's insulin sensitivity.
For example, a 52-year-old woman with a sensor glucose value of 220 mg/dL, correction factor 50, and one trend arrow pointing straight down (ie, blood glucose is dropping by 2–3 mg/dL/min) would subtract 2.5 units from the insulin amount she would otherwise take for a given carbohydrate amount she's about to eat. (Advice on rounding is also provided for patients who inject with pens that don't provide half-unit dosing.)
On the pediatric side, a 16-year old with a reading of 75 mg/dL, correction factor 25, and two arrows pointing up (ie, glucose is rising by >3 mg/dL/min), would add 3.0 units to the usual calculation.
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"These new guidance documents simplify the approach to adjust for trend. While there are many factors, such as exercise, illness, or stress that can alter glucose levels, CGM trend arrows can provide information about where the glucose is likely to be within the next 15 to 30 minutes. The new fine-tuning of dose adjustments takes into account what that glucose level is likely to be in the next half hour or so," Dr Laffel explained.
A Practical Approach to Using Trend Arrows on the Dexcom G5 CGM System for the Management of Adults With Diabetes. Pdf in full text. Free
Advice for CGM Trend Arrow Data to Adjust Insulin Doses in Diabetes
Miriam E Tucke. Pdf in full text. Free
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