Review: Use of Diabetes Technology by Patients With Cystic Fibrosis

Almost all individuals with cystic fibrosis (CF) have some degree of abnormal glucose tolerance, and up to 20% of adolescents and 50% of adults develop CF-related diabetes (CFRD). Continuous glucose monitors, insulin pumps and automated insulin delivery systems have the potential to decrease the burden of CFRD.

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Melissa S. Putman, MD, a dual-trained adult and pediatric endocrinologist in the Diabetes Clinical Research Center at Massachusetts General Hospital, Jordan S. Sherwood, MD, a pediatric endocrinologist at the center, and colleagues recently reviewed diabetes technology in the Journal of Clinical and Translational Endocrinology with an emphasis on CFRD. This summary focuses on practical clinical concerns.

Continuous Glucose Monitors (CGMs)

CGMs use a subcutaneous sensor to measure glucose concentrations every five to 15 minutes. Trend arrows convey the rate of glucose rise or fall, allowing the user to predict impending hypo- and hyperglycemia.

Glycemic targets—Consensus guidelines published in Diabetes Care recommend targets of 70% time in range 70-180 mg/dL, <5% time in the hypoglycemic range <70mg/dL (1.2 hours per day), and <30% time in hyperglycemic range >180 mg/dL (7.2 hours) for most patients with type 1 or type 2 diabetes. Given the association between time in range and hemoglobin A1c, and the recommended A1c goal of ≤7% for CFRD, the authors of the review recommend similar goals for patients with CFRD.

Alarms—CGM users can decide whether to use vibratory and/or audible alarms to detect actual and impending hypo- and hyperglycemia. This choice should be made carefully because alarm fatigue is a common reason for CGM discontinuation. For patients with CFRD, the authors suggest considering the patient's A1c, hypoglycemia awareness and lifestyle factors that may affect alarm tolerance.

Diagnostic imaging—CGM systems are either worn on the skin for seven to 14 days or implanted in the arm for 90 days. All manufacturers warn against exposing CGMs to MRI, CT, X-rays and diathermy, a problem because sensors are covered in limited supply by insurance companies and can't be reinserted once removed. Individuals with CF are at a particular disadvantage since they often require diagnostic imaging.

Insulin Pumps

Insulin pumps provide a continuous subcutaneous infusion of rapid-acting insulin infusion, which more closely mimics physiologic insulin secretion than injection-based therapy does. Basal rates, carbohydrate ratios, correction factors and target blood sugars can all be programmed by the time of day.

There are multiple rationales for insulin pump use by patients with CFRD:

• Efforts to optimize caloric intake often rely on carbohydrate-containing foods that are rapidly absorbed and cause substantial postprandial glycemic excursions
• Most individuals with CF have pancreatic insufficiency, and fat digestion often remains abnormal even with pancreatic enzyme replacement therapy, leading to rapid gastric emptying and substantial postprandial hyperglycemia
• Gastroparesis occurs in approximately one-third of patients with CF, according to a systematic review reported in Scientifica (Cairo)
• CF is associated with varying degrees of insulin resistance that can change over time related to chronic inflammation, infections and glucocorticoid therapy

Insulin pumps have advanced features that allow patients with CFRD to better customize insulin delivery in the setting of unpredictable gastric emptying, postprandial excursions and varying degrees of insulin resistance:

• Mealtime insulin can be delivered over an extended interval with combination boluses (one portion of the insulin is delivered immediately and the other is delivered over a longer period of time)
• Temporary basal rates allow the user to increase or decrease basal insulin delivery by a percentage of the baseline dose for a specified time period; the ability to customize basal rates by time of day also allows lower overnight basal insulin rates, which are commonly required given the physiology of CFRD

These features may be particularly useful in individuals with CFRD who require tube feeds.

Automated Insulin Delivery (AID) Systems

AID systems use CGM glucose values to automatically increase basal insulin delivery or deliver automated correction boluses of insulin to prevent or treat hyperglycemia. These devices can also attenuate or stop basal insulin delivery to prevent or treat hypoglycemia.

All commercially available AID systems were developed specifically for patients with type 1 diabetes. It's important to consider that in patients with CFRD, endogenous insulin secretion paired with automated AID insulin delivery may lead to reactive postprandial hypoglycemia.

The authors often start with a less aggressive correction factor for patients with CFRD. For those who have significant endogenous insulin secretion, lower basal rates may also be required in the overnight hours.

Patient Education Needed

In a 2021 survey published in Diabetes Technology & Therapeutics, 75% of U.S. youth and adults with CFRD reported CGM use but only 29% reported insulin pump use. 19% had formerly used CGM and 28% had formerly used insulin pumps. Negative experiences or perceptions were embarrassment about wearing the device, skin irritation, high cost, increased worry about glycemia and pain related to device use.

Considering the potential for diabetes technology to decrease the burden of CFRD, strategies are needed to promote device uptake and sustained use. More research may improve health insurance coverage, and expanded CFRD-specific patient education should address excessive worry and pain. The latter is uncommon when devices are used properly.

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