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

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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.

Safety risks are few, minor

Insertion of the sensor can pose minor safety risks, including infection, inflammation, and bleeding. Adverse events reported in 1 study consisted mainly of mild sensor site reactions such as blisters, bullae, edema, and erythema, none of which required treatment.⁶ The CGMS must be removed prior to magnetic imaging studies and the devices are not approved for use on airplanes. When the FreeStyle Navigator sensor is removed, a portion of the membrane polymer is left in the skin. The company reports no health effects in clinical studies, aside from sensor site reactions mentioned above, but long-term effects of sensor membrane fragments remaining in the skin are unknown.⁸

CGMS have the potential to reduce diabetic complications

FAST TRACK

Glycemic fluctuations may be an independent risk factor in the development of diabetic complications.

Glycemic fluctuations that occur throughout the day may be an independent risk factor in the development of diabetic complications.^9-11 Continuous monitoring that can detect such fluctuations could, potentially, reduce complications, but further studies are needed to determine whether CGMS users actually experience fewer complications. Several studies have shown a relationship between postpran-dial glucose fluctuations and macrovascular disease.^12-14 An analysis of data from the Diabetes Control and Complications Trial (DCCT) showed that A1C, mean blood glucose, and glycemic variability were independent risk factors for severe hypoglycemia.¹⁵ Reducing glycemic fluctuations may, therefore, reduce the risk of severe hypoglycemia.

CGMS data can change behavior, reduce hypoglycemia. The data a CGMS generates could be used to adjust medications or diet on the basis of real-time glucose levels, identify glucose trends, and aid in pattern management by providing retrospective, nearly continuous glucose values. One study evaluated the benefit of using a CGM in 90 type 1 and type 2 patients receiving insulin.⁴ All patients wore the monitor at home and at work during daily activities. Patients were randomized to a control group that was blinded to their glucose data and an experimental group that saw the display readings, could review trends, and received alerts and alarms from the system.

The results showed that the group that saw the display spent 21% less time in a hypoglycemic state and 26% more time in the target glycemic range than the control group. Nocturnal hypoglycemia was also significantly reduced in the group that had access to the display. These improvements were seen even though no prescribed plan to adjust therapy on the basis of glucose readings was in place, and must therefore have been the result of diet or insulin changes patients made on their own initiative in response to their CGM readings. Thus, in this study, providing more frequent glucose readings to patients improved safety of insulin and glycemic control.

Studies have also been done comparing the efficacy of CGM and traditional monitoring systems on hemoglobin A1C.¹⁶ These studies revealed a trend toward lower A1C with the use of CGMS, but the results were not statistically significant (0.22%; 95% confidence interval, -0.439% to 0.004%; P=.055).

Crossing the barriers to adoption
Before CGMS can become widespread in the primary care setting, barriers to their adoption must be addressed. Some clinicians continue to be dubious about the accuracy of the readings because CGMS measure interstitial glucose levels, rather than blood glucose. As we have seen, studies have been published that indicate a high level of accuracy for CGM readings, but more research needs to be done.

In the real world of the caregiver’s office, physicians and patients will have much to learn before CGMS come into widespread acceptance. Patients and providers both need to learn to use the new equipment and how to apply the data it provides. Physicians and patients will need to take account of the time lag before a CGMS reading catches up with a standard reading, and check with a standard blood glucose meter before making medication adjustments. Patients will need to understand the time to onset and peak of their insulins so that they can make appropriate adjustments.

Providers will have to find ways to incorporate the technology into their already busy clinical practice. Integrating CGMS data into electronic medical records or downloading data before scheduled office visits may streamline the process.

So where does this leave you, the busy family physician?
CGMS can provide useful information to select patients, making it possible for them to alter their diet and lifestyle choices and make better insulin treatment decisions. Although CGMS may not be able to eliminate the need for traditional self-monitoring of blood glucose entirely, using the 2 methods together does offer additional advantages. These new devices may help prevent hypo- and hyperglycemic episodes, improve patients’ quality of life, and potentially reduce the likelihood that complications will develop. Long-term studies will be necessary to confirm these potential benefits.