Q&A: CGM metrics may not provide accurate health data for people without diabetes
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Key takeaways:
- People without diabetes using a CGM have a glucose management indicator 0.59% higher than their laboratory-measured HbA1c.
- More studies are needed to analyze whether CGM use benefits people without diabetes.
Continuous glucose monitoring has been firmly established as beneficial for helping people with diabetes understand their glucose profile, but whether these metrics translate for people without diabetes is still unclear.
In a study published in Diabetes Technology & Therapeutics, researchers found a discordance between glucose management indicator (GMI), a CGM metric that estimates HbA1c, and laboratory-measured HbA1c. In an analysis of data from 153 children and adults without diabetes who wore a masked CGM for 10 days, the cohort’s mean GMI was 0.59% higher than laboratory-measured HbA1c. Additionally, 71% of participants had a difference between GMI and HbA1c of 0.4% or more, a percentage much greater than the 39% of adults with diabetes who had a difference between GMI and HbA1c of 0.4% or more in the original GMI study published in 2018.
Viral N. Shah, MD, associate professor of medicine and pediatrics in the adult clinic of the Barbara Davis Center for Diabetes at the University of Colorado Anschutz Medical Campus and lead author on the study, said the research was important because the number of people without diabetes using CGM has increased in recent years.
“Based on the findings from our study, it would not be appropriate to use GMI as a substitute for HbA1c in people without diabetes,” Shah told Healio. “GMI will overestimate HbA1c by about 0.6%, and it is possible that it may misclassify many people without diabetes as prediabetes.”
Healio recently spoke to Shah about the rise of CGM use among people without diabetes, why people without diabetes should exercise caution in interpreting CGM data and whether new or revised metrics could benefit people without diabetes.
Healio: Your study noted CGM use among people without diabetes is rising. Why are more people without diabetes using CGMs?
Shah: There are many start-up companies promoting CGMs as adjunct to lifestyle modifications to help people either improve well-being and metabolic health, prevent progression of prediabetes to diabetes, or weight loss. This has been going on for a while now, but there has been more proliferation of these companies recently.
Healio: Why was it important to analyze differences between GMI and HbA1c in people without diabetes and what are some of the reasons there was such a large discordance between GMI and HbA1c?
Shah: With increasing CGM use by people without diabetes, it is expected that people will use CGM metrics, including GMI, to assess their health. GMI is a mathematical equation to estimate HbA1c from sensor glucose. The GMI equation was derived using sensor glucose from people with type 1 and type 2 diabetes. Therefore, it is possible that GMI may not work well for people without diabetes. We hypothesized that GMI may overestimate HbA1c for people without diabetes and, therefore, conducted our study.
GMI was derived for a population with diabetes with a mean HbA1c of 7.3%, where you would expect higher HbA1c compared to people without diabetes. Thus, we found higher discordance between GMI and HbA1c in our study for people without diabetes compared to people with diabetes.
When the first consensus was published in the Journal of Diabetes Science and Technology in 2013 on time in range and then modified in 2017 and 2019, the entire emphasis was on CGM use in people with type 1 and type 2 diabetes. They wanted to make sure that we are telling people about why these metrics are important, what are the goals and the recommendations. It was all based around managing type 1 and type 2 diabetes, there was never an emphasis on recommendations for creating metrics that are useful for people without diabetes. However, it may come in the near future. It was discussed at the Advanced Technologies & Treatments for Diabetes meeting that we need to start refining some of the metrics and giving more clarity to people that these metrics may be different for people without diabetes. There is momentum.
Healio: For people without diabetes, would experts look at adjusting reference ranges for existing CGM metrics or would they create new metrics?
Shah: It all depends on the consensus and who the experts are in that consensus group. Remember, the consensus is not evidence-based guidelines, it’s a starting point. Then, based on more evidence, they’re going to revise their recommendations.
We did publish data on CGM across the life span in people without diabetes. We also published some data on the exercise response and various meal responses in people without diabetes. We’re trying to create at least some literature around this so that it can be helpful in defining normal reference ranges in the future.
Healio: Have there been large studies analyzing whether CGM is beneficial for making lifestyle or dietary changes in people without diabetes?
Shah: No, not really. There have been some small-scale studies presented during various meetings that were not published, but they showed some benefit. There is one small study from the University of Michigan documenting a small change in some of the metrics over time in people with prediabetes. But there is not a really good phase 3 study with definite outcomes. An outcome is, for example, if I’m using CGM in people with overweight or obesity, and the reduction in weight is compared to the control group. If you are claiming it can improve athletic performance, is there any study around that part? If you are saying it improves metabolic health, is there any study to say that there is a definitive outcome? We need to do a lot of research before we can say that CGM is going to be useful for people without diabetes.
Healio: Should people without diabetes be using CGM at all? If they use CGM, what should they keep in mind as far as interpreting data?
Shah: In my opinion, CGM may be helpful to improve lifestyle and dietary changes and to improve adherence to lifestyle. However, we need more studies before I would recommend CGM to people without diabetes.
If people without diabetes use CGM, they have to remember that most CGM metrics, such as time in range or time below range or GMI, were developed for people with diabetes and not for people without diabetes. People without diabetes should not be using these metrics to assess their health status or changes in health status.
References:
- Bergenstal RM, et al. J Diabetes Sci Technol. 2013;doi:10.1177/193229681300700234.
- Bergenstal RM, et al. Diabetes Care. 2018;doi:10.2337/dc18-1581.
- DuBose SN, et al. J Diabetes Sci Technol. 2021;doi:10.1177/1932296820905904.
- Shah VN, et al. Diabetes Technol Ther. 2023;doi:10.1089/dia.2022.0544.
- Shah VN, et al. J Clin Endocrinol Metab. 2019;doi:10.1210/jc.2018-02763.
- Yost O, et al. JMIR Diabetes. 2020;doi:10.2196/21551.
For more information:
Viral Shah, MD, can be reached at viral.shah@cuanschutz.edu.
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