Clinical Targets for Continuous Glucose Monitoring Data
An international consensus group has recommended clinical targets to help health care professionals and patients use continuous glucose monitoring data to guide managing diabetes.
Richard M. Bergenstal, MD, talks about the latest clinical targets for people with diabetes who use continuous glucose monitors (CGMs). An international group of experts on continuous glucose monitoring developed the targets, which were published in 2019 and focus on the amount of time a person’s blood glucose levels are within specific ranges. Meeting these clinical targets can help improve diabetes management and lower the risk for diabetes complications.
Q: You were part of an international group that recommended clinical targets for people who have diabetes and use CGMs. How did the group develop these targets?
A: The first step was to develop standardized continuous glucose monitoring metrics. Over the past decade, the Park Nicollet International Diabetes Center and many investigators, including myself, have been working on this issue.
The effort began with an international consensus meeting in 2012. It took until 2019 to develop the 10 standardized, clinically useful metrics for continuous glucose monitoring. These metrics are included in the American Diabetes Association (ADA) Standards of Medical Care in Diabetes—2020. The metrics include time in range (TIR)—time in the target blood glucose range of 70 to 180 mg/dL—as well as time below range (TBR) and time above range (TAR).
The second step was to decide on clinical targets for these metrics, so health care professionals and patients would know what values to strive for.
Another international consensus group convened, and the resulting report, Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations from the International Consensus on Time in Range, was published in Diabetes Care in 2019. We recommend the following clinical targets for CGM blood glucose readings for most people who have type 1 or type 2 diabetes
- TIR 70-180 mg/dL: more than 70 percent
- TBR below 70 mg/dL: less than 4 percent
- TBR below 54 mg/dL: less than 1 percent
- TAR above 180 mg/dL: less than 25 percent
- TAR above 250 mg/dL: less than 5 percent
The report also recommends time-in-range targets for older and/or high-risk individuals with type 1 or type 2 diabetes and for pregnant women with type 1 diabetes.
Q: Why are data about time in ranges important? How can meeting these targets improve diabetes management?
A: The clinical targets may be aspirational for some people with diabetes. We based the targets on evidence in the literature to ensure that reaching these targets was possible and would reduce the risk of acute and long-term complications. For example, studies have shown that 70 percent TIR approximately correlates with an A1C of 7 percent. An A1C of 7 percent is a long-standing goal for reducing the risk of diabetes complications, if a person can achieve this goal safely.
A couple of good studies have shown that using continuous glucose monitoring to help manage type 1 diabetes during pregnancy improves neonatal outcomes. A JDRF-funded study, Continuous Glucose Monitoring in Women With Type 1 Diabetes in Pregnancy Trial (CONCEPTT), found the use of CGM led to an increase in TIR by 7 percent and this improved pregnancy outcomes. This research has led to more routine use of continuous glucose monitoring during pregnancy and showed that even small increases in TIR have clinical benefits.
This research informed the 2019 international consensus report statement that every 5 percent increase in TIR is clinically important for all people with type 1 or type 2 diabetes. For patients who are significantly below the target of 70 percent TIR and may feel discouraged, health care professionals can emphasize that every 5 percent increase in TIR will have clinical benefits.
Q: How can health care professionals work with their patients who use CGMs?
A: First, you can use continuous glucose monitoring data in shared decision-making with patients. The Ambulatory Glucose Profile (AGP) is a standard one-page report that includes the core continuous glucose monitoring metrics and targets, along with a visualization of the patient’s daily glucose profile. You can review and discuss the AGP with patients during clinic visits or phone calls. For example, if the AGP shows that your patient isn’t reaching the target of 70 percent TIR, you can encourage your patient to steadily work to increase TIR by at least 5 percent before the next visit or phone call. If your patient has too much TBR, or hypoglycemia, you can review the retrospective continuous glucose monitoring data with your patient to see when during the day or night hypoglycemia most often occurs. Then you can agree on appropriate changes in lifestyle or medications to minimize this risk of hypoglycemia.
Second, you can teach patients how to use real-time continuous glucose monitoring data to effectively manage their diabetes. Many patients are looking at their continuous glucose monitoring data 10, 20, or 30 times a day. We want to support them and teach them how to use the data they are looking at to help improve their TIR.
For example, patients can view real-time glucose data to see which foods consistently make their glucose values rise too high and can easily notice how effective exercise can be at lowering their glucose levels. Before they eat, patients can check the glucose data for trend arrows that show whether their blood glucose levels are heading up or down and adjust their food intake or pre-meal insulin dose accordingly.
Q: How has continuous glucose monitoring affected diabetes management? How does continuous glucose monitoring data compare with information from traditional diabetes tests, such as the A1C test?
A: Continuous glucose monitoring has really transformed managing type 1 diabetes and probably diabetes in pregnancy. It also has the potential to make a huge impact in type 2 diabetes, but more research is needed there.
The A1C test is great because it’s been around for a long time and has been our gold standard metric for assessing a person’s risk for diabetes complications. However, the A1C test is an average measure of blood glucose and doesn't pick up hypoglycemia or glucose variability. Also, the A1C test is not accurate in many situations—for example, if a patient has iron deficiency or significant kidney or liver disease—and the A1C value can also vary considerably depending on each individual’s red blood cell lifespan.
Continuous glucose monitoring not only indicates a person’s risk for long-term complications but also serves as a much better tool for understanding how to effectively manage diabetes than the A1C test. Continuous glucose monitoring data are more meaningful to people with diabetes, allowing them to see their actual blood glucose values and understand where they may be struggling to keep them within the ideal target range. By responding to the continuous glucose monitoring data in real time and by having intermittent discussions about their overall glucose patterns with their health care team, patients are engaged and empowered to improve their diabetes management.
Q: What research is being conducted on the use of continuous glucose monitoring data?
A: Research has shown that continuous glucose monitoring is invaluable in managing type 1 diabetes. Continuous glucose monitoring is now the standard of care, and most clinicians feel it should be the first technology used to help manage diabetes, as opposed to the previous practice of starting with an insulin pump as the first advanced technology. There are some barriers to adopting continuous glucose monitoring technology, such as the cost and the hassle of wearing a device on the skin all day and night. Areas that require more research include
- which people with diabetes should move to a closed-loop system—a CGM and an insulin pump—for automated insulin delivery and when
- whether continuous glucose monitoring should be used to manage gestational diabetes
- which patients with type 2 diabetes might benefit the most from the use of continuous glucose monitoring
We particularly need studies on using continuous glucose monitoring as a lifestyle guide. Many of us—clinicians, dietitians, and diabetes educators—feel that when patients who are overweight or who have type 2 diabetes see their glucose profiles for the first time, it’s an amazing “A-ha!” moment. Continuous glucose monitoring could be an incredibly powerful motivating tool to encourage lifestyle changes, but that's a hypothesis that needs to be studied.
Continuous glucose monitoring sub-studies have been added to the NIDDK-supported Epidemiology of Diabetes Interventions and Complications (EDIC) study and the Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness (GRADE) study. Since these studies started, continuous glucose monitoring has become an important tool. For example, the GRADE study is a randomized trial examining how four different diabetes medications affect A1C. Now, we can expand the study findings to see how these medications also affect a person’s glucose profile by reviewing their continuous glucose monitoring data. That research will be very valuable and helpful in planning future diabetes studies.
Q: Is there anything else that health care professionals should know about using continuous glucose monitoring data to help improve diabetes management?
A: Health care professionals should take continuous glucose monitoring data seriously. The glucose management indicator (GMI)—which used to be called the estimated A1C—is one of the 10 core metrics and is an important marker. If you have adequate continuous glucose monitoring data—14 days of data, with the CGM active at least 70 percent of the time—then the blood glucose data really represent a person’s day-to-day life. The GMI shows what the patient’s A1C would be if they continued with the same general glucose levels for the next 30 days.
I want health care professionals to know that, in some cases, a patient’s GMI and A1C might not agree. Instead of being upset that there is a mismatch between the laboratory A1C and the GMI, give special attention to the GMI value, which can be used to guide safe, personalized diabetes management decisions. In many cases the GMI, in my opinion, is probably more clinically relevant for making management decisions for an individual, while the A1C is a standard population-based risk marker for diabetes complications.
How do you use continuous glucose monitoring data to help patients improve diabetes management? Tell us below in the comments.