A conversation with Jessica Castle, M.D., about the benefit of continuous glucose monitoring for type 2 diabetes patients not on insulin

Continuous glucose monitoring led to larger A1C reductions than routine finger-stick testing, according to the results of the Dexcom-sponsored CONNECT study.

Participants using the Dexcom G7 lowered their A1C by an average of 1.6 percentage points over 26 weeks, from a baseline of 8.8%. That was 0.9 points more than the control group. Among participants with a baseline A1C above 10%, the CGM group saw an average reduction of 3.1 points. Median daily sensor use was 97%, according to a Dexcom news release, and a six-month extension phase is underway to evaluate outcomes through 12 months.

Jessica Castle, M.D., adult endocrineologist and vice president of global affairs at Dexcom, recently sat down with Managed Healthcare Executive to discuss what these results could mean for the future of type 2 diabetes monitoring.

The interview has been edited for length and clarity.

MHE: What are the different types of diabetes, and how are they treated?

Castle: Type 1 diabetes is an autoimmune disease in which the immune system attacks the insulin-producing cells in the pancreas. People with type 1 generally need insulin for survival. Type 2 diabetes involves insulin resistance and the body not producing enough insulin to manage glucose effectively. It accounts for about 90% to 95% of people living with diabetes in the U.S.

Type 2 diabetes treatments vary. They can include lifestyle changes, oral medications, GLP-1 medicines or insulin. The CONNECT study focused on people with type 2 diabetes who were not taking insulin, a group of more than 20 million people in the U.S.

MHE: What is a continuous glucose monitor?

Castle: A continuous glucose monitor is a device that measures glucose using a tiny wire inserted just under the skin to measure glucose in the interstitial fluid, the fluid around the cells. The Dexcom G7, for example, provides a reading every five minutes and sends it to a smartphone. Depending on the sensor, it can be worn for about 10 to 15 days.

MHE: This study looked at the CGM use of patients with type 2 diabetes not on insulin. Why has this group received less research attention in the past?

Castle: CGMs were first studied and used for people with type 1 diabetes, then for people with type 2 diabetes taking multiple insulin injections and later for those using basal insulin. The CONNECT study gave us an opportunity to test CGM in people with type 2 diabetes who aren’t taking insulin, a large population that had received less study.

MHE: In the study, what was considered routine care, and how did the Dexcom G7 compare with it?

Castle: Routine care involved using a blood glucose meter for finger-stick testing. The groups had the same number of visits and the same amount of education. The main difference was whether participants used a meter or a CGM.

Finger-stick testing gives you a few snapshots, while CGM is more like watching a movie. It provides glucose data throughout the day. That can help people see how meals, medication or a walk after dinner affect their glucose. In the study, the CGM group lowered A1C by 1.6 percentage points, which was 0.9 percentage points more than the routine-care group. They also improved time in range and had less hypoglycemia.

Sometimes when you lower high glucose, you can get glucose that is too low. In this case, we saw both of those things get better, which is fantastic because you don't want to trade one for the other.

MHE: Why is reaching an A1C below 7% significant?

Castle: Participants started with average A1C levels in the high 8s. The American Diabetes Association recommends a target below 7% for many people with diabetes because high glucose can contribute to complications affecting the eyes, kidneys, nerves and heart. About twice as many participants in the CGM group reached that target compared with routine care.

MHE: How did participants use their CGM day to day?

Castle: People could check their glucose whenever they wanted, and the data could also help them learn over time. For example, they might see how a particular food affects their glucose or whether walking after dinner helps. That information can help people make choices that work for them, such as changing portion sizes, pairing a food with exercise, or choosing something different.

If I think back to my time caring for people with diabetes, oftentimes people would have these ‘aha’ moments when they were wearing the CGM. Take breakfast cereal as an example. Breakfast cereal is one of the most processed foods, and with things like corn flakes, people will see this really rapid spike in glucose. People learn what works for them, and they might make a different decision like a smaller portion size or pairing food with exercise.

Participants also wore the sensors 97% of the time. That’s a high rate, and it suggests participants continued using the device because they found it useful.

MHE: Were the benefits consistent across different groups of participants?

Castle: The study found benefits across the groups examined, including by age, sex, medication type and socioeconomic status. That was encouraging because it suggested that people across those groups could use CGM information to make changes and improve their diabetes management.

MHE: What about insurance coverage, including for people using CGM for health and wellness?

Castle: Some people with type 2 diabetes who aren’t taking insulin have CGM coverage, but Medicare does not yet cover it for that group. The Stelo Glucose Biosensor, Dexcom’s over-the-counter product, is a separate product for health and wellness and is currently an out-of-pocket expense. There may also be an opportunity for glucose monitoring to support prevention in the future.

MHE: Why might people taking GLP-1 medicines see additional benefits from CGM?

Castle: GLP-1 medicines are among the most potent glucose-lowering treatments for type 2 diabetes, but the study found a significant benefit from adding CGM. CGM may help people and their clinicians see when glucose remains high and decide whether a treatment adjustment is needed. It can also show how lifestyle changes affect glucose and provide feedback if someone misses or stops taking a medication.

MHE: What is the main takeaway you hope readers have from the CONNECT study?

Castle: CGM can be a valuable tool for people with diabetes, including people with type 2 diabetes who aren’t taking insulin. The CONNECT study adds evidence for a population that some might have assumed could manage with finger-stick testing alone.

MHE: What’s next for this research?

Castle: We’re looking at how improvements in glucose measures might translate into health outcomes. Data presented at the European Association for the Study of Diabetes conference included a GLP-1 subgroup analysis, in which CGM users taking GLP-1 medicines saw a 0.9-percentage-point A1C benefit. Another analysis estimated a 16% reduction in the proportion of participants at high risk for heart problems over the next 10 years.