Yes – Continuous Glucose Monitoring and Insulin Pumps Improve Glycemic Control
Consider the case of a 33-year-old teacher who has a toddler in preschool, regularly attends Pilates classes, and is in her second pregnancy. Her privacy is limited, and her lunchtime varies by at least 30 minutes. In her first pregnancy, when she used multiple daily injections (MDI) for insulin injection, her hemoglobin A1c at 36 weeks’ gestation was 7.2%, and her baby’s birth weight was 4,200 g. This time around, she cannot get her fasting blood glucose under 110 mg/dL without experiencing marked hypoglycemia around 3:30 a.m.
In her case, the demonstrated benefits of continuous glucose monitoring (CGM) and an insulin pump (for continuous subcutaneous insulin infusion, or CSII) make this method of insulin administration a compelling – and even obvious – choice over MDI. A glucose sensor and insulin pump would improve her glucose control, bring down her HbA1c, and lessen the frequency and severity of hypoglycemic episodes, while better meshing with her lifestyle.
Dr. Thomas R. Moore
She is far from the only type of patient who would benefit, however. Modern CSII pumps (with Bolus Wizard calculators) have been around for a decade, yet we significantly underutilize them. Many, if not most, insulin-requiring pregnant women are good candidates for glucose sensors and insulin pumps.
CSII improves glucose control by providing "background" changes in insulin dosing to match the complexities of metabolism in pregnancy, and CGM (as opposed to self–blood glucose monitoring) improves glucose control by removing the fear of unexpected lows, which is a big issue in my patients, and by warning of impending highs.
Together, today’s equipment also improves patients’ ability to administer insulin in social and business settings. The equipment is also easily programmable and understandable to women who routinely use electronic devices.
A Cochrane systematic review of CSII vs. MDI in pregnancy, published in 2007, unfortunately was not that telling for obstetrics, as only two of the seven available randomized trials were deemed appropriate for meta-analysis. While the mean birth weight was higher in the CSII group, there were no significant differences in macrosomia or any other outcomes, and the reviewers warned they could not draw any conclusions because of the dearth of data. It is important to note, too, that the studies involved ’90s-style pumps (Cochrane Database Syst. Rev. 2007 [doi:10.1002/14651858.CD005542.pub2]).
Fortunately, outside of pregnant populations, we see quite a bit of data on CSII v. MDI. For instance, a 2010 Cochrane systematic review of CSII v. MDI covering 23 randomized controlled trials of 976 nonpregnant patients with type 1 diabetes found a statistically significant difference in HbA1c favoring CSII (–0.3%), as well as a reduction in severe hypoglycemia and higher quality of life scores (Cochrane Database Syst. Rev. 2010 [doi:10.1002/14651858.CD005103.pub2]).
A randomized, controlled, crossover trial published in 2006 called the 5-Nations Trial similarly showed that CSII treatment in individuals with type 1 diabetes resulted in lower HbA1c, lower mean blood glucose level, less fluctuation in glucose levels, and higher quality of life than MDI (Diabet. Med. 2006;23:141-7).
CGM technology is rapidly evolving. A randomized controlled trial published this year found that patients receiving CGM spent significantly less time in hypoglycemia each day and had a concomitant decrease in HbA1c (again –0.3%, approximately). Normoglycemia was significantly longer (mean of 17.6 v. 16 hours per day). The 120 type 1 patients in the study had been randomly assigned to either receive real-time CGM or perform conventional self-monitoring (while wearing a masked CGM device) (Diabetes Care 2011;34:795-800).
Another smaller study of patients with type 1 diabetes or gestational diabetes mellitus being treated with MDI found that nocturnal hypoglycemic events dropped significantly when the patients switched to CGM.
Granted, the false alarms that occur with glucose sensors can be disconcerting, the equipment is expensive, and patients have to enter a series of finger-stick blood sugar readings into the monitor for calibration. Still, most patients place a value on being able to get real-time blood glucose readings at any time, even when asleep, busy, or distracted. And they can always temporarily suspend their system – to get ready for bed, for example, or to go to Pilates classes.
Dr. Moore is professor and chair of reproductive medicine at the University of California, San Diego. He said he had no relevant financial disclosures.
No – There Is Little Data Showing Improved Outcomes
I use these tools in less than one-third of my patients with type 1 diabetes, and only rarely in patients with type 2 diabetes or gestational diabetes. There is very little evidence about the efficacy and implications of monitoring. Because of this, and because it is expensive, many payers do not reimburse for continuous glucose monitoring (CGM).