Continuous glucose monitors (CGMs) are wearable devices that track blood sugar levels in real time.
They are helpful for people with type 2 diabetes to manage their blood sugar. In 2024, the U.S. Food and Drug Administration approved CGMs for over-the-counter use, including by people who do not have diabetes.
But it’s still unclear how useful these devices are for people without diabetes.
Researchers from Mass General Brigham studied CGM data from people with type 2 diabetes, prediabetes, and normal blood sugar levels. They found that CGM results match up well with HbA1c—a standard blood test that shows average blood sugar over a few months—for people with diabetes.
But this match becomes weaker in people with prediabetes and disappears completely in people with normal blood sugar.
The results were published in the journal Diabetes Technology and Therapeutics.
Dr. Jorge A. Rodriguez, the lead author, explained that CGMs are great tools for people with diabetes. But for others, the numbers shown on the CGM don’t match the results of the HbA1c test. For people without diabetes, CGMs cannot replace the HbA1c test to measure long-term blood sugar control.
The study looked at 972 adults aged 40 and up. Participants were from the University of Alabama, the University of California, San Diego, and the University of Washington. They wore a Dexcom G6 CGM, which checks blood sugar every five minutes, for up to 10 days.
Researchers compared CGM results with HbA1c test results taken at the beginning of the study. They looked at eight CGM measurements, including average blood sugar, time spent in a healthy range, and how much blood sugar levels changed throughout the day.
They found that in people with diabetes, CGM results closely matched HbA1c. In people with prediabetes, the connection was weaker. In those with normal blood sugar, there was almost no connection. These results stayed the same even when they considered other health factors like body weight.
CGMs were originally made for people with diabetes, so it makes sense that they work best for this group. In people without diabetes, blood sugar levels naturally rise and fall with meals and physical activity, but these short-term changes don’t affect HbA1c.
For people without diabetes, CGMs may still be helpful in showing how food or exercise affects blood sugar right away. But they should not be used to measure long-term blood sugar health.
The researchers say it’s important to be cautious when using CGMs in people without diabetes. More research is needed to find out if CGM data can identify people at risk of developing diabetes even if their HbA1c is normal. They also stress that everyone should have access to helpful health technologies.
Dr. Rodriguez added that CGMs may still be useful for people without diabetes who want to understand how their body responds to food and activity. But these devices are not a replacement for professional medical tests like HbA1c.
The study is published in Diabetes Technology & Therapeutics.
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