Advances in Continuous Glucose Monitoring
New drugs, technologies, and treatment approaches for diabetes are revolutionizing the way the disease is understood and managed. The most consequential new technology is continuous glucose monitoring (CGM), which has been described as the single most important advance for people with type 1 diabetes since the discovery of insulin. Randomized controlled trials and observational studies leave no doubt as to the benefits of CGM. For people with persistently high glucose levels who may have under-recognized and under-treated their hyperglycemia, CGM data provide motivation and guidance for therapy intensification, and CGM use has been consistently associated with favorable reductions in A1C levels. For people with problematic hypoglycemia, alerts provided by CGM systems provide the basis for acting before the symptoms become severe or debilitating. CGM data can also be shared in real time, providing valuable insight and peace of mind to spouses or parents of children with diabetes and allowing them to intervene in the face of impending hypoglycemia.
When CGM first emerged in 2000 there were several challenges facing early adopters, including lack of pediatric indications, short wear times, complex training requirements, interfering substances such as acetaminophen falsely elevating CGM glucose, and required use of a separate dedicated receiver display. Additionally, CGM required fingersticks to calibrate the devices and were adjunctive to blood glucose monitoring, necessitating additional fingersticks before making diabetes treatment decision. However, advancements in CGM have changed the value proposition. Due to improved accuracy, some CGM devices no longer require calibrations, some can be used for diabetes treatment decisions without the need for confirmatory fingersticks (non-adjunctive use), and alert performance has significantly improved, minimizing the nuisance of false alerts. Other advances used in some systems have included automating sensor deployment and use of alternate devices such as smartphones and insulin pumps to display the CGM glucose data. The ubiquity and connectivity of smartphones allows alerts and alarms to be shared in real-time allowing remote monitoring by family or caregivers. The integration of CGM data in some insulin pump systems is now allowing some early forays into the automation of basal insulin infusion rates to reduce the risk of hypoglycemia. The FDA recently authorized the marketing of a new CGM — Dexcom’s G6. This system has many of the improvements: it is factory calibrated, replaces fingersticks for treatment decisions, provides customizable alerts when glucose is high, low, or rapidly falling into hypoglycemia, blocks acetaminophen, connects to smart devices, and allows data sharing with loved ones. As a Class II medical device, some changes to the G6 System that would have required FDA premarket approval as a Class III device may now be reviewed by the FDA in less time, promising more rapid innovation in the field. Clearly, CGM technology today is not CGM as it was.
Despite advances in hardware and software, only a minority of patients who could benefit from CGM systems actually have CGM prescribed. Category unawareness and cost are contributors to the low adoption rate, but recent data show that adoption has quadrupled among people with type 1 diabetes in the past 7 years. Other barriers to prescription are being addressed. Insurance coverage has greatly expanded to include most people with type 1 diabetes and many plans also cover people with type 2 diabetes using insulin. Documentation requirements have been greatly reduced in many health plans. Importantly, accumulated glucose data can be retrospectively summarized and reviewed by patients and clinicians using either brand-specific tools (Dexcom’s Clarity, Abbott’s LibreView, or Medtronic’s CareLink) or the brand-agnostic Ambulatory Glucose Profile. Retrospective reviews can reveal otherwise-hidden glycemic patterns and better inform lifestyle or therapy recommendations.
Poorly-controlled diabetes is common among insulin-using patients in the US- fewer than 1/3 of patients are meeting their ADA-recommended A1C goal and almost half have A1C values in excess of 8%. The need to avoid severe hypoglycemia while maintaining near-normal glucose concentrations is complicated by insulin’s narrow therapeutic index. The information provided by CGM systems empowers patients and their healthcare professionals to set and reach their glycemic goals, often without the need for new therapeutic agents or escalation from insulin injections to insulin pumps.
In the late 1970s and early 1980s, home blood glucose meters replaced urine glucose testing as the standard of care for routine glucose monitoring. CGM represents a sea-change in diabetes management as a replacement for blood glucose monitors, as a new foundation on which to build precision treatment plans for diabetes, and as the core technology for automated insulin delivery systems. Until a “perfect” risk-free insulin or a viable strategy for pancreatic beta-cell replacement is found, CGM should be viewed as the standard of care for diabetes and should be considered for all patients using insulin.
David Price, MD, is Vice President of Medical Affairs at Dexcom. He is responsible for leading the strategy, design, and interpretation, of clinical trials and usability studies. He supports or leads discussions with regulatory agencies, payers and strategic accounts. Dr. Price previously worked at LifeScan and was responsible for developing clinical decision support solutions and has numerous patents related to integrating decision support solutions into medical devices. Dr. Price received his medical degree from the Ohio State University and completed his residency at the Maine Medical Center and his fellowship at the Joslin Diabetes Center and Harvard Medical School.
