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The holy grail of diabetes treatment is to mimic the way the pancreas works, constantly monitoring the amount of glucose in the blood and changing the amount of insulin being produced in response. The advent of continuous glucose monitoring (CGM) is an important step toward meeting the first criterion.
"We are now going to be able to go from getting information on blood sugar status three or four times a day to over 300 values a day," says Satish Garg, MD, professor of medicine and pediatrics at the University of Colorado School of Medicine and director of the Adult Program at the Barbara Davis Center for Childhood Diabetes in Aurora, Colo. "Generally the primary care physician [PCP] may not see 300 values for a given patient in a year. You are talking about a wealth of information that patients and physicians have to learn how to integrate into practice."
HOW CGM WORKS
CGM systems consist of a wireless, pager-like monitoring device that receives information from a sensor inserted under the skin that detects glucose oxidase in the interstitial fluid. Glucose meters are still a necessary component of CGM. Since interstitial and blood glucose may differ, CGM systems depend on the patient's entering blood glucose levels every 12 hours or so to teach the computer how the glucose oxidase levels correlate with the glucose meter results.
The U.S. Food and Drug Administration (FDA) approved DexCom's STS Continuous Glucose Monitoring System in March and Medtronic's MiniMed Paradigm in April. FDA approval is pending for Abbott's FreeStyle Navigator (DOC News, August 2006).
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With the interactive DexCom, measurements are taken every 5 minutes, and patients can read those glucose values in real time or view glucose trends and graphs. In addition, the device can be programmed to sound an alarm when glucose is either too high or too low (<55 mg/dl is a critical alarm, indicating that patients should immediately contact their physician, and the 80 mg/dl alarm alerts patients that they still can treat the problem themselves according to whatever protocol they have worked out with their physician). The sensors should be replaced every 72 hours, something patients can learn to do on their own.
The Medtronic device is "blind" and collects data during the 72 hours it is in place before it is removed and the information downloaded for graphing and analysis.
WHICH PATIENTS AND PROVIDERS WILL USE IT?
Because CGM is a new technology, currently no generally accepted clinical guidelines exist for its use.
"I do not see a lot of use for type 2 patients," says Howard Wolpert, MD, director of the Insulin Pump Program at the Joslin Diabetes Center in Boston. "The early adopters will be those who are in intensive diabetes management programs, such as individuals with brittle diabetes and unstable blood sugars, or those with frequent hypoglycemic episodes."
Other physicians agree that insulin use will be the major defining criteria, as opposed to type of diabetes.
Jeffry Lindenbaum, DO, is a family practitioner in Yardley, Penn., and has diabetes. "The most important thing is that [CGM] identifies fluctuations in blood sugars, especially episodes of hypoglycemia," he says. "This is its greatest value."
Who will be the major care manager of CGM over the next few years is the subject of some controversy.
"It is not that I am dismissing the PCPs," Wolpert says, "[but] I think it wouldn't be fair to expect them to be playing a major role in guiding the patients when most diabetologists haven't yet had much direct experience. It has only been a few months since the FDA approved use of the device."
Garg disagrees, saying not only is it possible, but it is imperative that PCPs become comfortable with CGM as quickly as possible. "There are around 2,000 endocrinologists in the nation, and not even 50% are well versed in this technology," he says. "There will never be more than 10% of all patients with diabetes seen by an endocrinologist, and someone has to treat the other 90%.
"The only way to solve the problem is to look at it from the primary care side and decide how we can empower them to do what is needed," Garg continues. "They will go back to their offices and, trust me, they will do a lot better job than we [endocrinologists] can do."
The manufacturers recommend patients attend a 45-minute session to learn how to use either of the available systems, how to insert the sensor probe, and how to analyze the acquired information. Wolpert expresses concern that PCPs will not be able to take the time to do the teaching and follow-up required, especially while reimbursement issues are being worked out.
On the other hand, Garg says about 50% of payers in his practice are paying for the integration of glucose values, education, and advanced or extended visits for patients using CGM. He suggests that a monthly clinic starting 8–10 patients on the sensor could generate an increase in income to help offset the increase in expenses, while at the same time improving long-term diabetes outcomes.
Lindenbaum suggests two methods for implementing a CGM program in a primary care practice. The PCP can purchase the system and run it as part of the practice. This entails becoming proficient with insertion, disconnection, maintenance, generation and interpretation of reports, and education of patients for successful use. The other option is to contract with an outside company to handle all of the above. The individual practice should look closely at reimbursement issues with its particular mix of payers before deciding which, if any, pathway is best.
Start-up costs with the Medtronic device are roughly $2,000 for each glucose monitor, cables to connect to a computer, and other accessories. The monitor is reusable.
Assuming that a practice already has a computer, the initial costs for the DexCom monitor are minimal, as the manufacturer supplies the computer program and training. Cost to the patient is around $800 for the monitor and another $35 for each sensor.
"I think every PCP, if they are going to take care of diabetes, must
know about CGM," Lindenbaum says. "Diabetes cannot be treated on a
quarterly basis when the diabetologist can see [patients]. You need to see
them once a month or more often for continuous education, monitoring of their
glucose logs, and making sure they are getting required physical exams such as
eye and foot care." 
Footnotes
The U.S. Food and Drug Administration offers general information about glucose meters and monitors at www.fda.gov/diabetes/glucose.html, and about the DexCom STS Continuous Glucose Monitoring System and Medtronic MiniMed Paradigm at www.fda.gov/cdrh/pdf5/p050012.html and www.fda.gov/cdrh/pdf/p980022.html, respectively.
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