Most people with type 1 diabetes rely on daily insulin injections, not an insulin pump, to control their blood sugar levels and the disease. Now, two new studies evaluating the use of continuous glucose monitoring (CGM) in these patients find modest benefits for controlling hemoglobin A1C levels and blood sugar fluctuations.1,2
With CGM, "'you do get a moderate improvement in the A1C, and a little less hypoglycemica," says Mayer B. Davidson, MD, professor of medicine at Charles R Drew University and David Geffen School of Medicine, Los Angeles. He wrote an editorial to accompany the two studies, published in JAMA.3
However, he also noted downsides, including the device's invasiveness, expense, and the need for the patient to commit to learning how best to use the device. And finger sticks to test blood glucose are not eliminated, he points out. "Two times a day you have to finger stick to calibrate [the device]," he tells EndocrineWeb.
CGM has been studied in those with type 1 diabetes on the insulin pump, but not studied in those who use injections. The system includes a tiny electrode, or glucose sensor, inserted under the skin to measure glucose in tissue fluid. The electrode is connected to a transmitter that relays the information to a monitoring and display device. Alerts are sounded if glucose drops too low or rises too high.
DIAMOND Study: In one study, called the DIAMOND (Multiple Daily Injections and Continuous Glucose Monitoring in Diabetes), researchers evaluated 158 adults with type 1 diabetes who were using multiple daily insulin injections and had hemoglobin A1C levels of 7.5 to 9.9%. (In general, non-pregnant adults with diabetes are advised to aim for a goal of 7%.)4
They assigned 105 people to use CGM and 53 to usual care, taking blood glucose readings throughout the day.
After 24 weeks, those in the CGM group had a drop in A1C of 1% on average while those in the comparison group dropped an average of 0.4%.1
The CGM group also had fewer low blood sugar periods—a median (half longer, half less) of 43 minutes a day, compared to 80 minutes in the comparison group. The number of severe low blood sugar events was the same, two in each group.
The CGM device was well accepted, says study researcher Roy Beck, MD, PhD, executive director of the Jaeb Center for Health Research, Tampa. "About 90% at six months were still using it daily or nearly every day," he tells EndocrineWeb. The benefits, he says, ''are at the same levels as what we see in pump users'' who use CGM.1
The satisfaction scores are even higher, Dr. Beck says. That could be because the devices tested now have been improved from in years past, he says.
GOLD Study: In the second study, known as the GOLD (Glycemic Control Treated with Multiple Daily Insulin Injections) study, researcher Marcus Lind, MD, PhD, of the University of Gothenburg in Sweden, assigned 161 men and women with type 1 diabetes and an A1C of at least 7.5% who took multiple injections daily to either CGM or conventional treatment for 26 weeks. Then, they had a break or washout period for 17 weeks before each group switching to the other group for the next phase of the study.
The A1C, on average, was better while on CGM 7.92% compared to 8.35%. Low blood sugar was more common when CGM was not used. Five had it when they were in the conventional group, compared to one instance in the CGM group. The difference in A1C was .4, significant from a statistics point of view.2
Until now, GCM has ''been accepted mostly by pump patients," says Dr. Davidson. A number of studies on the use of CGM in pump users has shown moderate improvement, he says. "However, only about 40% of [those with] type 1 diabetes are on pumps."
So the research focusing on the benefit of CGM for those on injections was the logical next step, he says.
Although the two studies did show benefit, Dr. Davidson says, CGM is ''invasive and expensive."
Several companies make the monitors. The one used in the DIAMOND study, the Dexcom G4, costs about $1200 for the receiver and transmitter, according to Tomas C. Walker, a Dexcom spokesperson. The box of four sensors is $349; each sensor is labeled for 7-day use.5
It is often reimbursed by insurance, Walker says. Medicare approval is being finalized, he says.6
"This was a landmark study," says Walker of the Diamond study, ''that needs to change the way we think about using CGM and who can benefit from it—clearly CGM can be used in and benefit almost anyone with type 1 diabetes."
Patients who opt to use CGM need to commit to learn the approach, Dr. Davidson says, and physicians must be well-trained in the use of the device and be able to explain it well to patients.