Continuous glucose monitoring: What pharmacists need to know

The technology of continuous glucose monitors (CGMs) continues to evolve, and pharmacists can play a key role in helping patients navigate new systems coming on the market.

Gary Scheiner “They’re being used a lot more often. The devices have gotten quite a bit better, and just about everyone with type 1 diabetes or insulin-dependent type 2 diabetes can benefit from them,” said Gary Scheiner, MS, CDE, owner and clinical director, Integrated Diabetes Services, Wynnewood, Penn.

There are challenges. While private insurers typically cover the expensive CGMs, Medicare and Medicaid don’t. Patients must follow through with daily calibrations and accept living with a transmitter attached to their bodies. And the devices aren’t yet as accurate as fingerstick measurements of blood-sugar levels.

Still, CGMs can make a big difference in the lives of patients, allowing them to closely track their blood-sugar levels throughout the day and get better warnings of impending problems - especially hypoglycemia - so they can take action. 

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The final frontier

Hypoglycemia control is a final frontier in terms of diabetes control, said Irl B. Hirsch, MD, professor of Medicine, Division of Metabolism, Endocrinology, and Nutrition, University of Washington.

“We’re seeing dramatically less eye and kidney disease in type 1 diabetes patients, and the majority of people can do reasonably well with their hemoglobin A1c levels, thanks to fingerstick glucose testing and current insulin strategies,” he said. “The real challenge is eliminating life-threatening hypoglycemia, which we know is common.”

Hypoglycemia occurs when there’s too much insulin in the body. Blood-sugar levels drop, leading to symptoms such as dizziness, sweating, and headache. In diabetics, hypoglycemia may cause seizures and loss of consciousness. 

Hypoglycemia appears to be more common in people with type 2 diabetes than many patients realize. Hirsch and his colleagues found that type 2 diabetes patients over 60 years of age, who have an average of 40 years of illness, spend an average of 99 minutes a day in a hypoglycemic state, including 60 minutes with a glucose level of under 60 mg/dL. (Hypoglycemia is defined as a level below 70 mg/dL.)

To make matters worse, Hirsch said, “As patients live longer with diabetes, their ability to be aware of their hypoglycemia continues to diminish.”

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The importance of keeping track

While they’re not perfect, CGMs allow patients to track whether their glucose levels are trending up or down, Hirsch said, information that can be crucial. “If you have someone who’s getting insulin before a meal or driving a car, and they have a blood sugar level of 105, the sensor lets you know if the level is stable, going up, or trending downward,” Hirsch said. “Even if you’re doing fingerstick glucose-testing six or seven times a day, you don’t get that. If the trend is going down, you may eat more food or subtract some insulin. You’ll do something differently.”

Diabetes educator Scheiner puts it this way: “It’s one thing to know what your blood sugar is. It’s another to know which way it’s headed.”

Available options

H. Peter ChaseReal-time glucose monitoring isn’t new. The technology has been around since the 1990s, but it didn’t really begin to take off until 2000, said H. Peter Chase, MD, professor of pediatrics at the University of Colorado School of Medicine’s Barbara Davis Center for Childhood Diabetes.

Now, two companies, Medtronic and Dexcom, produce glucose monitoring devices. Dexcom offers the G4 Platinum System with Share, which transmits glucose statistics to a monitor and to certain smartphone models via Bluetooth. A new model, the G5TM Mobile Continuous Glucose Monitoring System, was scheduled to come to the market in September 2015 and doesn’t require information to go through a receiver on its way to a smartphone.

David PhamMedtronic offers several models, including the MiniMed 530G system, which features an insulin pump and stops the pumping of insulin when glucose reaches specific low levels; the MiniMed Paradigm Real-Time Revel System, which includes an insulin pump; and the Guardian Real-Time System, which doesn’t include a pump.

“If you can use a smartphone, you will have no problems using continuous glucose monitoring,” said David Q. Pham, PharmD, BCPS, CDE, associate professor, Pharmacy Practice and Administration, Western University of Health Sciences, Pomona, Calif. Indeed, FDA has approved the marketing of smartphone apps that allow users to share their glucose data with other users in real time, a boon for parents who want to track levels in their children.

User responsibility

Users do have to take action each day and each week to keep the devices working properly.

First, using an applicator, they must insert a filament sensor (about a centimeter long, approximately the size of a hair) under the skin, said Scheiner. A transmitter is also required.

David Swaschnig“The dimensions vary slightly between devices, but they generally are the approximate size of a quarter in diameter and 4 quarters in height,” said pediatric nurse practitioner David Swaschnig, CDE, a diabetes educator and children’s CGM coordinator at the University of Colorado School of Medicine’s Barbara Davis Center for Childhood Diabetes. “Use shouldn’t restrict any activities, as they are waterproof, and there are numerous methods for taping to help with better adherence.”

Users also must calibrate the devices by taking old-fashioned finger-stick measurements twice a day. According to Chase, research has found that 40% of patients who try the devices  keep up with their use only for about a year. “They don’t want to do the calibrations twice a day,” he said, “or they’re unhappy with the accuracy.”

Pros and cons

Indeed, the devices aren’t as accurate as needle sticks. For one thing, they’re 10 minutes behind: They measure glucose levels in the skin’s subcutaneous layer, and it’s always about 10 minutes behind the actual blood-sugar level, because glucose needs time to transfer from the intravascular space into the subcutaneous tissue, Chase said. “It’s not a blood reading that’s instantaneous, like when you do a finger poke.”

The devices are useful because information about levels can be downloaded by physicians for review, said Chase, author of the book “Understanding Insulin Pumps and Continuous Glucose Monitoring,” which can be purchased from the Children's Diabetes Foundation at Denver.

As for choosing between the two brands of machines, “the two competitors are very similar in a lot of respects,” said Swaschnig. “Users tend to have very polarized viewpoints, similar to the Apple/Android debate. If an individual struggles with or has issues with one system, they may  often find greater benefit in the counterpart.”

Dexcom devices are more accurate, Chase said. “Some people get frustrated by Medtronic values not matching their values as closely as they’d like.” However, the insulin pump shut-off capacity in one of the Medtronic devices is especially helpful to patients with severe hypoglycemia, especially children, Chase said. Ninety percent of children’s severe hypoglycemia incidents occur at night; in adults, it’s 50%, he said.

Potential users

Who are the best candidates to use the devices? “The biggest thing is that the person has to want it,” Chase said. “They need to have been compliant in taking care of their diabetes relatively well. People who aren’t compliant are less likely to keep using it.”

It’s also important to check on insurance coverage, since Medicare and Medicaid don’t cover the devices, he said. The systems can cost $1,000, he said, with ongoing costs of around $400 a year. 

The devices are most useful to patients with type 1 diabetes. In 2011, the Endocrine Society recommended their use for children and adolescents with type 1 diabetes, and for adults who have demonstrated they can use them on a nearly daily basis.

However, “most people with diabetes could benefit from either personal or diagnostic use,” said Swaschnig. “Anyone interested in having better blood glucose control and more insight into their diabetes can benefit greatly, in particular those who struggle with wide fluctuations in the blood glucose levels, very young children, and those who are very physically active.”

However, he said, “individuals with high levels of anxiety around their blood glucose, leading to the impulse to overcorrect or rush to treat, may not be great candidates, as seeing sensor glucose readings frequently may overwhelm them. This is not to say that those with anxiety can’t or won’t do well, but this needs to be assessed prior to going on a device.”

Randy Dotingais a medical writer based in San Diego.