Melissa Lee, diagnosed with Type 1 diabetes at 10, models what she says is an easy-to-use continous glucose monitor. (Lauren Hanussak/KQED)
Continuous glucose monitors have been around for over a decade, but reductions in cost and improvements in quality have enticed more patients and doctors to try them out.
For Melissa Lee, the worst part of diabetes isn’t pricking her finger to check her glucose level or changing her diet to keep her blood sugar in check. Rather, it’s the constant worry and mental calculations.
“You have to think about what did I eat last, how much insulin did I take for that, where is my blood sugar now, which direction is it trending, and then based on that, what am I going to eat?” she says. “You’re making these educated guesses about how much of a really volatile hormone [insulin] to take, and that is mentally exhausting.”
Lee, 38, who was diagnosed with Type 1 diabetes when she was 10, recounts ruined dates, missed flights and abandoned excursions, all because she was worried about her glucose level or forgot to bring a replacement for her insulin pump.
“You can go from being okay to being really not okay in a moment’s notice,” says Lee, who lives in Milpitas, California and works as the director of community relations at Bigfoot Biomedical.
To relieve some of the burden for the estimated 9.3 million people who use insulin to regulate diabetes, medical device makers have introduced new ways to monitor glucose and administer insulin.
Better Glucose Management
Continuous glucose monitors, or CGMs, have been around for over a decade, but poor quality and high costs have been barriers to use, says Irl Hirsch, who holds the Diabetes Treatment and Teaching Chair at the University of Washington School of Medicine. But improvements on both fronts lead him to believe that CGMs will soon become the standard of care. At his own clinic, 60 percent of patients use one.
“The financial impact and the insurance coverage is not the barrier that it used to be,” Hirsch says. What’s more, “The quality and the accuracy of these things have just gotten better.”
CGMs measure glucose levels not in blood but in the interstitial fluid, which surrounds the cells just underneath the skin. A sensor sticks onto the body, typically on the upper arm or abdomen, with a small, flexible needle that penetrates the skin. The sensor takes a reading every 5 to 15 minutes and transmits that information to a separate receiver or a smartphone app, which patients can check at any time. The reading shows their current glucose level and a trend graph for the last eight hours. If the number is high and rising, the patient can bring their glucose down using insulin; if it’s low and dropping, they need to eat some sugar, fast.
“It's very exciting technology. I think it's really revolutionizing diabetes care,” says Kathleen Dungan, an associate professor of medicine at Ohio State University who runs the school’s endocrine clinical trials unit. “In a perfect world, everybody with diabetes would benefit from some form of this technology.”
Too Little Insulin
Every time you eat, your pancreas pumps out insulin to help your cells extract glucose from the blood and use it for fuel. In Type I diabetes, the pancreas stops producing insulin, while in Type II the cells can’t utilize the hormone properly. In either case, too little insulin causes excessive blood glucose levels. Chronic high blood sugar, or hyperglycemia, can lead to heart disease, kidney disease, stroke, nerve damage, blindness and loss of limbs.
In contrast, too much insulin results in low blood sugar, or hypoglycemia, which can cause weakness, dizzy spells, seizures, shaking, fainting and even death.
Patients typically use blood glucose meters that measure sugar levels in a drop of blood to determine if they need to take more insulin or not. However, having to prick your finger and draw blood to check your glucose level can be a major hurdle for maintaining normal blood sugar. Some patients may have aversions to needles, while others may have difficulty creating a sterile environment in which to take a reading.
CGMs aim to ease that pain and inconvenience. Dexcom and Abbott are two of the largest producers of CGMs, with Abbott’s FreeStyle Libre the newest device approved by the FDA, in September 2017.
The Libre sensors last for 10 days and cost $59 each. Sensors for Dexcom’s G4 or G5 system are $350 for a pack of four and have to be replaced every seven days. Patients also have to purchase a receiver, about $60 for the Libre versus $465 for the Dexcom G5. Finally, Dexcom requires a separate transmitter to send the glucose information to the receiver, another $595. Both companies’ devices are covered by major insurance providers and Medicare, so the actual cost to patients varies.
The Libre is the only monitor that doesn’t have to be calibrated daily with a traditional blood glucose reading, meaning patients never have to prick their fingers.
Studies show that patients who use a CGM have better control over their diabetes than patients who use traditional blood glucose tests. Doctors recommend patients check their glucose between 4 and 10 times per day, but in reality, only one-third of patients test themselves as often as they should. Abbott says patients using its device easily exceed this standard, checking on average 16 times a day.
Lee, who uses the FreeStyle Libre, says being able to easily check her blood glucose helps her know how it's affected by her diet. “You suddenly have this insight into how actions you took actually affected some kind of diabetes outcome,” she says.
Another Type 1 diabetes patient, Lisa Trahan, 33, yses the Dexcom G4 and says it’s “terrific.” Trahan, a clinical psychologist based in San Marcos, Texas, says the frequent readings provide her with more peace of mind, especially before exercising or eating. However, she still doesn’t trust the device enough to forego pricking her finger to double check the numbers.
“I can trust the CGM reading of my Dexcom G4 to be within 20 percent in either direction of my actual blood sugar reading,” she explains. But, she says, that range can make a big difference when tinkering with blood sugar or insulin. “I use the alert as a suggestion to check my blood sugar and go from there.”
Smarter Insulin Pumps
Besides checking blood sugar, the other part of managing diabetes is taking insulin, either with an injection or an insulin pump.
Traditional insulin pumps are preset to deliver different doses at certain times of the day. However, it can be difficult to match the correct dose to fluctuations in glucose levels that occur naturally throughout the day or because of diet or exercise. A patient or doctor can adjust the levels manually, but it requires complex calculations and typically isn’t done every day.
Medtronic’s MiniMed 670G, the first integrated CGM-insulin pump system approved by the FDA in 2016, aims to solve that problem. The 670G can vary the amount of insulin it delivers as often as every five minutes, in response to input from an integrated glucose monitor.
The only calculation patients have to make is to manually deliver a boost of insulin every time they eat that is proportionate to the number of carbohydrates in the meal. They also need to prick their fingers three times a day to calibrate the system.
Despite the excitement over the 670G, the price can be prohibitive, running between $6,000 and $9,000. Medtronic says some of the cost is covered by insurance.
A Debate Over Alarms
Because low glucose levels can be so dangerous, most monitors have built-in alarms that go off when a patient’s glucose has dropped too low. However, Abbott’s FreeStyle Libre does not. Hirsch, the diabetes expert from the University of Washington, says because of this he recommends Dexcom’s CGM, even though the Libre is less expensive and easier to use.
The MiniMed 670G also has an alarm, and to patient Ken Reutell, 67, from Petaluma, California, this is a great feature. In the past he’s had to call 911 and has even passed out because his blood sugar had dropped so low. He's used the 670G for six months and says the alarm alerts him well before he gets to that point. Other users, however, have complained that the 670G’s alarm is loud and goes off too frequently.
And while the device can alert a patient to a dangerously low glucose level, it can’t do anything about it because it doesn’t administer glucose.
“(W)hen you get too low, your liver starts pumping out more glucose. That’s something that insulin pumps don’t do yet,” Reutell laments.
Something for the next generation of devices, perhaps.
Get the best of KQED’s science coverage in your inbox weekly.