Continuous Glucose Monitors for All? Opinions Remain Mixed

The recent US Food and Drug Administration (FDA) clearance of two over-the-counter (OTC) continuous glucose monitors (CGMs) — Dexcom’s Stelo and Abbott’s Lingo — has sparked interest in potentially expanding their use to those without diabetes or prediabetes.
There are several valid questions about how the general population might benefit from CGMs. Can they motivate those struggling with overweight to shed pounds? Would they prompt users to follow more healthful eating patterns? Can they act as a canary in the coal mine, alerting users to prediabetes? 
The short answer to these questions is, we don’t know.
“Glucose levels fluctuate in everyone in response to meals, exercise, stress, etc, but there has been no credible research to support CGM use by most people who do not have diabetes,” Jill Crandall, MD, chief of endocrinology at Albert Einstein College of Medicine and Montefiore Health System in New York City, told Medscape Medical News.
“The utility of CGM for people without diabetes hasn’t been established and the drive to market CGM as an OTC device seems largely driven by financial considerations,” Crandall said. She advocates instead for a strategy directed at more meaningful objectives.
“For now, efforts should be focused on making CGMs available to patients who will clearly benefit — ie, people with diabetes, especially those who are using insulin and those who are struggling to achieve desired levels of glucose control.” 
Nicole Spartano, PhD, assistant professor of medicine in endocrinology, diabetes, nutrition and weight management at Boston University’s Chobanian & Avedisian School of Medicine, Boston, agreed with this assessment.
“It is definitely too early to make recommendations for patients without diabetes based on their CGM data,” said Spartano, who also serves as the director of the Glucose Monitoring Station at the Framingham Heart Study in Framingham, Massachusetts. “We simply do not have enough follow-up data to tell us which CGM metrics are associated with higher risk for disease.” 
Spartano served as the lead author of a recent study showing time spent in various CGM ranges in a large cohort of individuals without diabetes using the Dexcom G6 Pro model. In the future, she said the data may be used to establish reference ranges for clinicians and individuals.
“We are working on another paper surveying diabetologists and CGM experts about how they interpret CGM reports from individuals without diabetes,” she told Medscape Medical News. Although the data are not yet published, Spartano said, “we are finding that clinicians are currently very discordant in how they interpret these reports.”
Potential Benefits Right Now
Satish Garg, MD, director of the Adult Clinic at the Barbara Davis Center for Diabetes at the University of Colorado Anschutz Medical Campus, Aurora, Colorado, and editor-in-chief of Diabetes Technology & Therapeutics, is convinced that glucose should be considered another vital sign, like blood pressure, pulse rate, respiration rate, and body temperature. Therefore, he sees the use of a CGM in people without diabetes as a way to build awareness and perhaps prompt behavior modification.
“Someone with an A1c of 4.9 on a normal day may notice that they’ve gained a little bit of weight, and if they use an OTC CGM and start seeing changes, it might help them to modulate their diet themselves, whether they see a dietitian or not,” Garg said.
He gave the example of “a natural behavioral change” occurring when someone using a CGM declines to eat a post-meal dessert after seeing their blood glucose had already risen to 170.
Wearing a CGM also has the potential to alert the user to high blood glucose, leading them to an earlier diagnosis of prediabetes or diabetes, Shichun Bao, MD, PhD, Diabetes Technology Program Leader at the Vanderbilt Eskind Diabetes Clinic of Vanderbilt University in Nashville, Tennessee, told Medscape Medical News. She has had cases where a family member of someone with diabetes used the patient’s fingerstick meter, found that their glucose was 280, and self-diagnosed with diabetes.
“It’s the same thing with the CGM,” she said. “If they somehow did not know they have diabetes and they wear a CGM and it shows their sugar is high, that will help them to know to see their provider to get a diagnosis, get treated, and track progression.”
Given the shortage of endocrinologists and long waits for appointments in the United States and elsewhere, it is very likely that primary care physicians will be the ones fielding questions from individuals without diabetes interested in purchasing an OTC CGM. Internist Douglas Paauw, MD, a professor at the University of Washington School of Medicine, Seattle, told Medscape Medical News, that for his practice, “the benefits outweigh some of the limitations.”
“I don’t really think somebody who doesn’t have diabetes needs to be using a CGM all the time or long term,” he said. “But I have used it in a few people without diabetes, and I think if someone can afford to use it for 2 to 4 weeks, especially if they’ve been gaining weight, then they can really recognize what happens to their bodies when they eat certain foods.”
Paauw added that CGMs are a more effective means of teaching his patients than them receiving a lecture from him on healthy eating.
“There’s nothing like immediate feedback on what happens to your body to change behavior.”
Similarly, William Golden, medical director at Arkansas Medicaid and professor of medicine and public health at the University of Arkansas for Medical Sciences in Little Rock, Arkansas, told Medscape Medical News, “It is difficult to justify coverage for CGMs on demand — but if people want to invest in their own devices and the technology motivates them to eat better and/or lose weight, then there are benefits to be had.” 
Potential Downsides
Although it may seem simple to use an OTC CGM to measure blood glucose on the fly, in the real world it can take patients time to understand these devices, “especially the first day or so, when users are going to get false lows,” Bao said. “Clinicians need to tell them if you don’t feel like your sugar is low and the device says it’s low, whether they do or don’t have diabetes, they should do a fingerstick glucose test to confirm the low before rushing to take in sugar. On the other hand, if they drink a lot of juice, their sugar will go high. So, it can create problems and false results either way.”
Many factors affect glucose, she said. “When you’re sick, glucose can go high, and when you’re very sick, in the ICU, sometimes it can be low. It depends on the situation.” Bao noted that certain vitamins and drugs can also interfere with readings.
Bao doesn’t see value in having people without diabetes monitor their glucose continuously. “If they want to see what foods or exercise do to their body, they will probably benefit from a short trial to gain some insight; otherwise, they’re wasting money,” she said.
Another potential downside is that there’s no head-to-head comparison data with the approved devices, Garg said. “But it’s clear to us that Stelo’s range is very narrow, 70 to 200, whereas the Lingo ranges are pretty much full, from 40 to 400 or 55 to 400. So, we don’t know the accuracy of these sensors.”
Golden observed that for certain patients, CGMs may lead to psychological distress rather than providing a sense of control over their blood glucose levels.
“I have had a nondiabetic patient or two that obsessed about their blood sugars and a device would only magnify their anxiety/neurosis,” he said. “The bottom line is that it’s a tool for a balanced approach to health management, but the daily results must be kept in perspective!”
Educate Patients, Primary Care Physicians
To maximize potential benefits for patients without diabetes, clinicians need to be well trained in the use and interpretation of results from the devices, Bao said. They can then better educate their patients, including discussing with them possible pitfalls surrounding their use. 
“For example, a patient may see that their blood glucose, as measured by a fingerstick, is 95, whereas the CGM says 140, and ask, ‘Which one do I trust?’”
This is where the patient can be educated about the difference between interstitial glucose, as measured by the CGM, and blood glucose, as measured by the fingerstick. Because it takes about 15 minutes for blood glucose to get to the interstitial tissue, there’s lag time, and the two measurements will differ.
“A discrepancy of 20% is totally acceptable for that reason,” Bao said.
She has also seen several examples where patients were misled by their CGM when its censor became dislodged.
“Sometimes when a sensor has moved, the patient may push it back in because they don’t want to throw it away. But it doesn’t work that way, and they end up with inaccurate readings.” 
At a minimum, Bao added, clinicians and patients should read the package insert but also be aware that it doesn’t list everything that might go wrong or interfere with the device’s accuracy.
Manufacturers of OTC devices should be training primary care and family practice doctors in their use, given the expected “huge” influx of patients wanting to use them, according to Garg.
“If you are expecting endos or diabetes specialists to see these people, that’s never going to happen,” he said. “We have a big shortage of these specialists, so industry has to train these doctors. Patients will bring their doctor’s data, and the clinicians need to learn the basics of how to interpret the glucose values they see. Then they can treat these patients rather than shipping all of them to endos who likely are not available.”
Paauw agreed that CGM training should be directed largely toward primary care professionals, who can help their under-resourced endocrinologist colleagues from seeing an uptick in “the worried well.” 
“The bottom line is that primary care professionals do need to understand the CGM,” he said. “They do need to get comfortable with it. They do need to come up with opinions on how to use it. The public’s going to be using it, and we need to be competent in it and use our subspecialists appropriately.”
Spartano received funding for an investigator-initiated research grant from Novo Nordisk unrelated to the CGM studies cited here. Garg , Bao, Paauw, Golden, and Crandall declared no relevant conflicts of interest.
Marilynn Larkin, MA, is an award-winning medical writer and editor whose work has appeared in numerous publications, including Medscape Medical News and its sister publication MDedge, The Lancet (where she was a contributing editor), and Reuters Health.
 
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