Make Sense of Glucose Data With Time-In-Range Targets
New time-in-range targets can help you make sense of your glucose data and better manage your diabetes
As continuous glucose monitors (CGMs) have become more accurate and popular over the past decade, a new way of determining glucose control has emerged. Called “time in range,” it could become an important tool to help you guide both medication and lifestyle management and limit the risk for diabetes complications.
The concept is straightforward: Your CGM crunches the data it gathers and tells you the percentage of time you’ve spent within a target glucose range, as well as how much time you’ve spent both above and below your targets. These details can offer helpful insight into how food, exercise, mood, and other factors cause fluctuations in blood glucose throughout the day. “It can help users understand what they’re doing well and what things can be acted on,” says Elena Toschi, MD, an endocrinologist at the Joslin Diabetes Center in Boston.
Currently, devices vary in the way that they display time in range, but experts are pushing for the data to be made uniform across all CGMs. “We hope in the next few years we’ll get there, so that it’s standard,” says endocrinologist Satish Garg, MD, director of the adult program at the University of Colorado–Denver’s Barbara Davis Center for Diabetes. “It would be nice to see time in range by the day, week or two weeks, or time of the day.”
The first time-in-range target guidelines were published last summer. Endorsed by the American Diabetes Association (ADA) and several other diabetes-focused organizations, the guidelines say that the goal for most people with type 1 and type 2 diabetes is at least 70 percent of readings between 70 and 180 mg/dl, or roughly 17 out of 24 hours in range each day. Different targets are provided for pregnant women and older people, as well as for those at higher risk for diabetes complications (see “Time-in-Range Targets,” below).
Recent studies suggest that the more time you spend in range, the less likely you are to develop certain diabetes complications. In one study, published in Diabetes Care earlier this year, researchers reported that as time in range decreased, the risk for developing both diabetic retinopathy and microalbuminuria—a risk factor for kidney disease—rose dramatically.
Another study in Diabetes Care, published in 2018, showed a link between time in range and retinopathy. The authors found that participants with more advanced retinopathy spent significantly less time in range. Recent research led by Irl Hirsch, MD, a professor of metabolism, endocrinology, and nutrition at the University of Washington in Seattle, suggests that less time in range may also be linked to neuropathy.
However, a lot more research needs to be done. Much of what’s understood about the link between time in range and diabetes complications comes from analyzing data collected years ago, before CGMs were in use. “It takes years to collect all the data about long-term complications, and so far we don’t have any long-enough CGM studies,” says Toschi.
For Garg, a member of the international panel that produced the guidelines, the introduction of time in range is part of a necessary evolution in diabetes management that recognizes both the promise of technology, specifically CGMs, and the shortcomings of A1C, the current gold standard for determining blood glucose control.
“We need to consider moving beyond A1C,” says Garg. “There’s a never-ending list of things that can interfere with blood glucose and therefore with A1C.” Kidney disease, liver disease, anemia, and other chronic conditions can skew the results of an A1C test. Even iron deficiency during menstruation can falsely elevate a woman’s A1C.
More important, A1C is an average of blood glucose for the previous three months or so. It doesn’t document the various highs and lows that people with diabetes may have during that period. “A1C does not represent a true, accurate measurement of glucose control,” says Garg.
Hirsch, who served on the panel with Garg, agrees. “If you just look at the A1C in such a case, you are potentially going to overtreat the diabetes,” he says. For example, an A1C of 7 percent may indicate well-managed diabetes—or it could be an average of high highs and low lows. Without knowing that, your doctor might prescribe medication in a dose that lowers your blood glucose into hypoglycemia territory. “With CGM, I have a much better and safer way to make decisions about therapy.”
And, Hirsch says, time in range helps self-management as well: “It’s a sophisticated but relatively simple-to-understand way to look at one’s diabetes management. You get much more information than you do from a simple A1C measurement.”
Does that mean A1C is on the way out? No. It has been and likely will remain the standard measure of diabetes management because it’s well established that A1C can be used to predict and help prevent diabetes complications.
“A1C has been a fundamental marker of management since the 1980s,” says Hirsch. “But we didn’t have the technology then that we have today with CGM. I don’t want to throw A1C away, but we have a better metric now.”
Both Garg and Hirsch consider time in range a useful complement to A1C. In fact, says Garg, research shows that spending 70 percent of the day in range equates to an A1C of 6.5 to 7 percent, the upper limit of the ADA’s recommended goal, while spending 80 percent of the day in range equates to an A1C of about 6.5 percent.
Up for Review
People with type 1 diabetes and those with type 2 who use insulin and have tight blood glucose goals (say, an A1C below 8 percent) will benefit the most from reviewing their time-in-range data. That’s because they’re most likely to fluctuate between highs and lows. And lows, says Hirsch, must be avoided as much as possible. “For people who take insulin, time in range can help minimize hypoglycemia, which can do some bad things for brain development in the young and [for] cognition in the elderly,” says Hirsch.
Research has yet to establish how often people should check their time-in-range status. However, Hirsch says, many people with diabetes find daily and weekly summaries to be helpful.
If you use the Freestyle Libre CGM, which requires you to scan the sensor to get glucose readings, the more scans you do each day, the more time you are likely to spend in range. Aim for more than 10 scans a day for best results.
If you have type 2 diabetes and don’t take insulin or use a CGM, you can feel comfortable continuing to use the A1C to set glucose goals. Still interested in time in range? Talk to your doctor about using a professional CGM for about two weeks to establish your time-in-range patterns and optimize them for better blood glucose management. Your doctor may recommend that you do this yearly to confirm that your time in range holds steady.
One barrier to the widespread adoption of time in range: the relatively limited number of people who use a CGM. Though the numbers have dramatically increased in recent years, fewer than 30 percent of people with type 1 diabetes use one.
Hirsch, who considers CGMs to be game changers in diabetes management, hopes that the number of users will continue to climb. He points out that insurance coverage of CGMs has improved, and Medicare now covers CGMs for anyone who uses an insulin pump, injects insulin multiple times a day, or checks their blood glucose at least four times a day.
At the end of the day though, the time-in-range data is meaningless unless both patients and health care providers take the time to review it. “It’s a new thing,” says Toschi. “We all have to learn how to use it, how to interpret it.”
The Individual Element
The new time-in-range guidelines standardize the amount of time people with diabetes ideally will spend in their recommended glucose range.
Making gradual changes is key. “Getting to the goal is important for avoiding long-term complications, but I want to get there without creating stress and anxiety in my patients,” says Toschi.
Remember: There’s no universal time-in-range goal. Yours will depend on your diabetes management needs and lifestyle.