November 2007

Continuous Glucose Monitoring: Is It the Right Fit?
By Juliann Payonk
Today’s Dietitian
Vol. 9 No. 11 P. 32

Continuous glucose monitoring (CGM), a way to continuously track real-time glucose readings, may not work best for all patients with diabetes, but it’s certainly revolutionary for many. Suzanne Pecoraro, RD, MPH, CDE, president of the Diabetes Education Society, Inc. and a copresenter of the session “Continuous Glucose Monitoring: Deal or No Deal?” at this year’s American Association of Diabetes Educators (AADE) annual meeting, says the session’s title “helps convey the idea that CGM is not a game and that there are several things an educator needs to consider before making recommendations for CGM. There are also several important issues a potential candidate needs to understand before making the ‘deal’ to use CGM.”

What Is It?
CGM systems consist of three distinct parts: a sensor, transmitter, and receiver. After a disposable sensor is placed just beneath the skin in the abdomen, a plastic catheter is inserted to measure interstitial fluid (ISF) glucose levels, says Pecoraro of the system she uses. Inserting the sensor, which must be replaced periodically, causes minimal discomfort and can easily be done by patients themselves.

The sensors for another CGM system, the MiniMed Paradigm REAL-Time system, can be inserted in any area with sufficient adipose tissue, says Pat Danahy, RD, CDN, CDE, a diabetes clinical consultant in New York. “There is a platinum electrode that is coated with glucose oxides that is left under the skin (ie, there is no catheter).”

The transmitter is a “device placed on top of the sensor. It converts the ISF signal to a glucose value and transmits this value to the receiver,” Pecoraro says. The receiver—a handheld device that can be worn on a belt or insulin pump or carried in a pocket or purse—then receives the transmitter signal wirelessly and displays glucose values every one to five minutes.

“The MiniMed Paradigm REAL-Time system is set up such that the transmitter attaches to the side of the sensor; the entire unit is about the size of a quarter. With this system, the ISF signal is sent from the transmitter to the pump/monitor, which then converts the signal to a glucose value once a finger stick calibration has been entered,” Danahy notes.

But CGM systems don’t only display real-time glucose values. With alerts and alarms, the system can also be programmed to let patients know when they’re heading for trouble. “These are warning sounds or vibrations telling the patient that his or her blood glucose is headed for a predetermined value—this may be a high or low value,” says Pecoraro. “The alert or alarm signals patients that their glucose is moving toward an out-of-target value, and they can then take steps to treat the situation,” she adds, which helps patients better manage their diabetes.

Trending arrows, which indicate the direction the glucose value is moving over time, are additional data shown on a CGM system. “If the monitor shows 100 milligrams per deciliter, the arrow would indicate whether the glucose is going up or down or is stable,” she says. “Depending on the circumstances, the patient can take some action to remedy the situation. For example, if the arrow is going down, the patient may want to treat with some carbohydrate to prevent a low blood sugar reaction.”

Anne Ruelle, RD, LD, CDE, CLSC, a copresenter with Pecoraro, says, “With appropriate instruction, the trend arrows allow the patient to really see a high or low is on its way and be able to stop the event. Minimizing the alerts and alarms makes life easier for the patient and those who love him or her.”

Good to Know
Although CGM offers many benefits allowing for more in-depth diabetes care, health professionals should do their homework before recommending this new technology. The following are some good points to remember:

Blood Glucose vs. ISF
Instead of blood glucose, the value that most health professionals are adept at evaluating in patients with diabetes, CGM displays ISF glucose. Similar to blood glucose, ISF values can lag several minutes behind blood glucose values. Pecoraro explains this lag time: “Interstitial fluid lag refers to the glucose level in the ISF, which is a different value than glucose in the blood. The glucose in ISF lags behind or ahead of the blood glucose depending on several circumstances.”

She says the glucose in interstitial fluid is roughly 10 to 15 minutes behind or ahead of blood glucose and 10% to 15% different than blood glucose, adding that ISF glucose correlates almost directly to cerebral glucose, the glucose level in the brain. Pecoraro advises health professionals to be aware of the many factors that can affect these levels: weight, hydration, pregnancy, illness, time of day in relation to food intake, and activity.

Calibration Is Key
While CGM can help alert patients to dangerously low overnight glucose levels, which can often go undetected, the system must be properly calibrated to maintain accuracy. Calibration is performed using blood glucose finger stick values, with several values required while the patient is wearing the sensor. Each system has different calibration schedules, but all systems calibrate using finger stick blood glucose values.

Danahy notes that MinMed’s system requires a minimum of two calibrations per day, although three to four calibrations are recommended and are typically done before meals, when blood glucose is stable.

However, Pecoraro stresses the importance of health professionals explaining this process in detail to their patients. She says, “If they calibrate at a time when the blood glucose is changing rapidly (ie, postmeal), this will affect the accuracy of the calibration,” which will then affect the accuracy of all values coming from the CGM system.

Adjunct Only
It is important to note that the FDA has currently approved CGM devices for adjunct therapy only, meaning patients cannot replace daily finger stick testing with CGM. Whereas the testing from finger sticks shows blood glucose levels at a certain point in time, the real-time continuous testing of CGM, showing movement of blood glucose over time, is presently only a supplement to help patients with better disease management.

“The FDA’s current approval is for this technology to be used in addition to diabetes therapy,” says Pecoraro, “which includes point-in-time blood glucose monitoring. Currently, the FDA does not approve the use of ISF glucose values for making decisions about diabetes therapy changes—for example, premeal insulin dose.” The lag time, as well as calibration and accuracy issues, requires confirmation of a blood glucose value prior to making a therapy decision, she says.

“Occasionally, patients who have not done research [on the technology beforehand] are disappointed to learn that CGM is not a replacement for finger sticks at this time,” says Danahy. “It simply takes the snapshot finger sticks and makes them into a motion picture.”

Not for Everyone
Although Pecoraro says patients with type 1 or type 2 diabetes can benefit from CGM when used properly, she adds that it is not for everyone. “Someone who does not feel comfortable with data, problem solving, and making therapy decisions” may not be the best candidate for the technology.

But age isn’t necessarily a factor with CGM, although she notes that it is currently only approved for adults aged 18 and older. “I believe the Abbott Navigator has been used successfully in a younger population,” she says, but that device is still pending FDA approval.

“I have patients as young as 10 years old and as old as 85 years old wearing CGM,” says Danahy. “Motivation to improve diabetes care and outcome is the best predictor of success with CGM.”

Ruelle agrees: “Age is not a consideration as much as the patient’s willingness and capabilities.”

Education
Do patients need to understand all the details of CGM to use or benefit from the technology? Pecoraro, who is presenting the upcoming Webinar series “Discover the Future of Advanced Diabetes Management” with the Diabetes Education Society, says yes: “Patient education is integral. It is important to understand calibration, lag time, and accuracy issues associated with CGM. People should not embark on any new therapy blindly.” (More information about these Webinars can be found here.

“Many of the patients I have trained on CGM have been very successful in using it. Most have done research on the product, so they have a general understanding of what the system can and cannot do,” Danahy says, adding that patients must do their homework before CGM training can begin. “Patients are asked to prepare for their hands-on training by reading their user guide, viewing a CD, and completing Medtronic’s Pump School Online, which is an online tutorial.”

If they have done the homework, she says the training goes smoothly but typically takes one and a half to two hours in person. “We review all material that patients need to know to be successful with their system. After the initial start-up, there are 24- and 72-hour follow-up phone calls. More phone calls are made as deemed necessary to ensure patient success.”

Once a patient has been wearing a CGM system, either the patient or health professional can download the data to view online and better assess the information. Danahy says that a review of CGM downloaded data is critical as well. “All patients are instructed to download their device’s data after five to seven days of wearing it. When reviewing data, I make sure I am not critical of patients’ actual blood glucose values. I am confirming that they are utilizing the system to optimize its performance. I do troubleshooting and answer questions they have about wearing the system.”

Often, patients are able to recognize their own issues. Whether not bolusing enough, overtreating a low, or needing more or less insulin, Danahy puts emphasis on trends. When repeated problems occur, she says many patients are savvy enough to come to their own conclusions, “but I always advise they review any potential changes with their provider.”

Danahy informs patients that learning to optimize the system may take weeks. “We advise them to wear a sensor continually for the first four to six weeks to maximize learning,” she says. “Studies show that patients who wear the system continually gain more benefits than those who wear it intermittently, or sporadically.”

Real-life Benefits
Although CGM’s accuracy and calibration issues may not make it a one-size-fits-all technology, Sheryl Bouchard, RN, CDE, of St. Joseph Diabetes and Nutrition in Bangor, Me., has seen real benefits.

She details patient M.S., who has hypoglycemia unawareness, and how CGM’s alerts have helped him treat overnight lows. “He lives alone and has been on an insulin pump for about four years. Despite frequent testing, his blood glucose levels remain erratic and drop so low he is unable to function. Until he got the real-time CGM system, he had to keep his blood sugar well above target levels. He was afraid to sleep at night, so he would set his alarm clock and wake up every two hours at night. Sleep deprivation was becoming a major issue for him. Now, his sensor alerts him when his blood glucose goes too low.”

She also describes one client’s CGM realization with type 2 diabetes management. “R.D. is on three oral diabetes medications. His physician wanted him to go on insulin, but he was resistant. Once he had the CGM completed, he saw just how out of control his blood glucose levels really were. So, it helped him to move forward to manage his diabetes with the insulin his body needed.”

CGM can also work for younger patients, such as college students. “A.L. was establishing care for insulin management and would be leaving for school out of state in 10 days. I needed data quickly,” says Bouchard. “The CGM system allowed me to see what his blood sugars were 24 hours a day. I brought him in daily and downloaded the CGM system to effectively make insulin adjustments and get him back to school on time.”

Ruelle says that she even witnessed how CGM alerted a client to an illness beyond diabetes. “Alice wore CGM for three days. Her blood sugars had been extremely elevated for months—[hemoglobin] A1c over 10. Her physician insisted the patient was eating and not compensating with insulin, but I knew her well and that could not be the case,” she says. “CGM revealed excursions with and without food. Lab tests later revealed her cancer had returned. Alice is in chemotherapy now. Her case would have been much worse had we not used the CGM and continued to resolve the problem.”

A Better-managed Future
Although relatively new, CGM is a technology that many health professionals hope will be around for years to come. “I have used CGM with my patient population for about four years. The majority of time has been with the sensor offering retrospective data; but in the last year since the availability of the real-time sensor, I use both,” says Bouchard.

She raves of CGM’s ability to evaluate “frequent unpredictable hypoglycemia, hypoglycemia unawareness, nocturnal hypoglycemia, exercise-related glucose control difficulties, and titrating control during pregnancy. Real-time CGM system monitoring enables the ability to make responsive corrections to unpredictably high and low blood glucose levels and learning through immediate feedback about which foods and physical activities adversely impact blood sugar levels.”

Pecoraro says that overall, CGM allows patients greater information about their blood glucose, which in turn allows for better decision making in diabetes self-care. “It will provide more information ... if used in a manner to help change diabetes therapies to keep blood glucose values in the target range with less fluctuation, CGM has the potential to reduce complications of diabetes,” she says.

As for CGM being the future of diabetes care management, Pecoraro says, “I think Dr. Daniel Einhorn made some helpful comments about CGM therapy when he presented at the American Association of Clinical Endocrinologists conference this past April. He identified the clear benefits—trends reveal secrets, alarms, safety, etc.—and he also laid out the challenges—the sensor can fail outright, can be inaccurate, can take time to acclimate, can wane, and can be unreliable at extreme highs and lows. Managing the data is also a very complex undertaking for both patient and clinician.”

However, Pecoraro says that the biggest indicator of CGM’s future is in what Einhorn noted as a typical response from patients using the technology: “It’s some of the most difficult, frustrating technology I’ve ever had, and I don’t know how I ever lived without it.”

— Juliann Payonk is an editorial assistant at Today’s Dietitian.

Living What You Preach
Pat Danahy, RD, CDN, CDE, a diabetes clinical consultant in New York, works with patients using continuous glucose monitoring (CGM), but she has also been using it herself since its FDA approval in April 2006. She may be one of the biggest advocates for the new technology because she sees its benefits firsthand.

“It has become a part of me. I do not have to wear it. I want to wear it,” she says. “I simply cannot live without it. During my 29 years of having diabetes, there were many days that I wished I had had this information: my wedding, my pregnancies. I remember a fellow educator asking me once why I would want to know my blood sugar continually. (This was many years ago, before any thoughts of real-time data existed.) All I could say to her was, ‘Why wouldn’t I?’ Now that I have the data, I cannot imagine having lived without it.”

Of the many lessons learned through CGM, Danahy says, “I have learned, most dramatically, that the analogue insulins do not work instantaneously for me and that I need to bolus earlier than I had been in the habit of doing.

“I have also been able to modify my basal settings for all those crazy female days of the month,” she adds. “I have been able to minimize the high and low excursion I have, and my [hemoglobin] A1c dropped 0.7 in the first two months of wearing CGM.”

Danahy appreciates the alarms that “keep me safe” but says viewing the graphs on the screen help her make more educated decisions about when she exercises, when she eats, what she eats, and when to bolus. “In terms of ease of use, CGM does require a little more forethought in order to calibrate the system properly. Calibration is best done when the blood sugar is fairly stable—ie, no recent meals or boluses,” she recommends.

One of CGM’s barriers is a lack of insurance coverage and the staggering cost to uninsured patients. “Several patients whose insurance will not pay have opted to pay out of pocket. The ‘Starter Kit,’ which includes the MiniLink transmitter, charger, inserter device, tape, and 10 sensors, retails for $999. Sensors are $35 apiece,” she says, adding that the monthly cost will vary dependent on how often the sensor is worn but that the current sensor only has a three-day FDA approval. An extended indication is being sought from the FDA by Medtronic.

However, CGM insurance coverage has been improving steadily, she notes. “In western New York, we have one local HMO approving the sensor system. Nationally, there are several large insurance companies approving. The rate of acceptance of the technology is growing rapidly. Patients are requesting, physicians are requesting, and insurers are responding.”

— JP