A new glucose monitoring option

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Applied Evidence

A new glucose monitoring option

J Fam Pract. 2010 February;59(2):81-88

By

Rachel Hrabchak, PharmD

James Taylor, PharmD, CDE

These new devices allow patients to measure glucose continuously, via a tiny sensor in the skin. Here’s how they work, and which patients may benefit from using them.

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References

1. Dexcom. The new SEVEN PLUS. Available at: www.dexcom.com. Accessed January 6, 2010.

2. FreeStyle Navigator Continuous Glucose Monitoring System Available at: www.freestylenavigator.com. Accessed January 6, 2010.

3. Medtronic Diabetes Available at: www.minimed.com. Accessed January 6, 2010.

4. Garg S, Zisser H, Schwartz S, et al. Improvement in glycemic excursions with a transcutaneous, real time continuous glucose sensor: a randomized controlled trial. Diabetes Care. 2006;29:44-50.

5. Weinstein R, Schwartz S, Bragz R, et al. Accuracy of the 5-day FreeStyle Navigator Continuous Glucose Monitoring System. Diabetes Care. 2007;30:1125-1130.

6. Garg S, Smith J, Beatson C, et al. Comparison of accuracy and safety of the SEVEN and the Navigator continuous glucose monitoring systems. Diabetes Technol Ther. 2009;11:65-72.

7. Medtronic User Guide, Guardian Real-Time Continuous Glucose Monitoring System. Appendix A: Sensor Accuracy, pp. 131-146. Available at: www.medtronicdiabetes.com/pdf/guardian_real_time_user_guide.pdf. Accessed January 11, 2010.

8. FDA Approves Abbott’s FreeStyle Navigator Continuous Glucose Monitoring System Available at: www.abbottdiabetescare.com/adc_dotcom/url/content/en_US/10.10:10/
general_content/General_Content_0000163.htm. Accessed January 6, 2010.

9. Brownlee M, Hirsch IB. Glycemic variability: a hemoglobin A1C-independent risk factor for diabetic complications. JAMA. 2006;295:1707-1708.

10. Hirsch IB, Brownlee M. Should minimal blood glucose variability become the gold standard of glycemic control? J Diabetes Complications. 2005;19:178-181.

11. Monnier L, Mas E, Ginet C, et al. Activation of oxidative stress by acute glucose fluctuations compared with sustained chronic hyperglycemia in patients with type 2 diabetes. JAMA. 2006;295:1681-1687.

12. DECODE Study Group. Glucose tolerance and mortality: comparison of WHO and American Diabetes Association diagnostic criteria. Lancet. 1999;354:617-621.

13. Donahue RP, Abbott RD, Reed DM, et al. Postchallenge glucose concentration and coronary heart disease in men of Japanese ancestry. Honolulu Heart Program. Diabetes. 1987;36:689-692.

14. Temelkova-Kurktschiev TS, Koehler C, Henkl E, et al. Postchallenge plasma glucose and glycemic spikes are more strongly associated with atherosclerosis than fasting glucose or HbA1C level. Diabetes Care. 2000;23:1830-1834.

15. Kilpatrick ES, Rigby AS, Goode K, et al. Relating mean blood glucose and glucose variability to the risk of multiple episodes of hypoglycemia in type 1 diabetes. Diabetologia. 2007;50:2553-2561.

16. Chetty VT, Almulla A, Odueyungbo A, et al. The effect of subcutaneous glucose monitoring (CGMS) versus intermittent whole blood finger-stick glucose monitoring (SBGM) on hemoglobin A1c (HbA1c) levels in type 1 diabetic patients: a systematic review. Diabetes Res Clin Pract. 2008;81:79-87.

PRACTICE RECOMMENDATIONS

• Practitioners and patients can use continuous glucose monitoring (CGM) data to modify medications and institute lifestyle alterations. A

• CGM systems must be calibrated with conventional blood glucose monitors to ensure accuracy. A

• CGM systems can set off an alarm to alert patients to glucose thresholds above and below established norms. A

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series

We all know that the key to optimal diabetes management is tight glucose control, which can be achieved with multiple daily fingersticks, good record keeping of the results, and appropriate modification of the medication regimen, diet, and exercise schedule.

But patients find the routine burdensome, and many skip fingersticks or abandon the process entirely. And even those who follow the program faithfully may find that it fails to protect them from unpleasant and potentially dangerous episodes of hyper- and hypoglycemia.

The newer technology of continuous glucose monitoring systems (CGMS) offers the promise of overcoming these limitations. But how do these new systems work and what does the evidence tell us about their potential benefits and remaining uncertainties? Read on.

The old way: Take a snapshot
The variables that affect blood glucose levels—meals and snacks, exercise or the lack of it, dosages and timing of medication, and stress, among others—keep changing throughout the day and night. The impact of these variables cannot be adequately captured in snapshot blood glucose levels taken at isolated moments in the patient’s day. Achieving glycemic control with blood glucose monitors can be difficult for some patients, especially since the data generated are dependent on the patient’s willingness and ability to self-monitor his or her glucose levels.

The new way: Monitor continuously

FAST TRACK

Continuous glucose monitoring systems measure the amount of glucose in the interstitial fluid every 5 minutes, throughout the day and night.

CGMS measure the amount of glucose in the interstitial fluid—not in the blood. These measurements are taken every 5 minutes or so, depending on the system. Each system consists of a sensor, transmitter, and receiver. The sensor is a fine wire—about the diameter of 2 human hairs—that sticks into the skin of the abdomen or upper arm and is kept in place by an adhesive pad. The transmitter fits on the sensor pad and sends information to the receiver via radio waves. Sensors are disposable; they last for 3 to 5 days and then must be replaced. The system is wireless, so your patient isn’t tethered to the equipment.

Calibration with a glucose meter is still necessary. To be sure that interstitial glucose measurements reflect actual blood glucose levels, currently available systems require daily calibration with conventional blood glucose monitors. Patients will still have to do fingersticks, but far less frequently. The FDA has approved CGMS for use only in conjunction with conventional glucose testing. Traditional glucose self-monitoring may also be necessary when CGM results do not correspond to symptoms patients are experiencing.

Receiver displays data, can set off an alarm. Glucose measurements from the CGMS are displayed and stored in the receiver, and the data can be downloaded to a computer using the manufacturer’s data software. Continuous readings over a 24-hour period for up to 7 days allow the user to detect variation and identify trends. High and low glucose value thresholds can be customized for the individual patient and fed into the system. When these thresholds are exceeded, an alarm will sound. The receiver displays directional arrows showing the rate of change in glucose levels, allowing the patient to predict—and possibly prevent—hypoglycemic episodes.

Impact of events can be noted. The systems also allow for input of additional information about events that may affect blood glucose levels, such as medication, exercise, and food intake. Patients can use information about how these events affect their glucose levels to adjust the prandial or basal insulin dose, modify the insulin correction algorithm, or adjust their diet. Patients can bring computer-generated charts and graphs to office visits as a basis for joint decision-making about their care. Short-term, periodic use of a CGMS in patients with type 2 diabetes may identify times when patients need more frequent self-testing or guide further therapy selection.

These systems are available now

The systems available in the United States include:

the iPro Continuous Glucose Monitor, Guardian Real-Time System, and Mini Med Paradigm Real-Time System—all from Medtronic, Inc.
the SEVEN PLUS, from DexCom
the FreeStyle Navigator, from Abbott.^1-3

The SEVEN PLUS and the FreeStyle Navigator are FDA approved for adults only. Pediatric versions of Medtronic’s MiniMed Paradigm and Guardian systems are approved for use in patients ages 7 to 17. All these systems require a prescription. For detailed comparisons of the features of these systems, see the TABLE.