Measure for Measure: How “Time in Range” May Be the Metric to Improve Diabetes Management

As more and more patients with diabetes embrace continuous glucose monitor technology, an international consensus group points to ways clinicians and patients can apply continuous glucose monitor data to minimize glucose highs and lows.

With more diabetes patients adopting continuous glucose monitors (CGM), endocrinologists are wrestling with questions about how best to use all that real-time data they provide.

An international consensus group believes that it is time for CGM data to assume its place as a major measure of glycemic control to avoid long-term diabetes complications.

Hemoglobin A1c provides useful information on a patient’s overall success at glycemic control, but it can’t provide guidance on how to improve it. In the August issue of Diabetes Care, the international group lays out state-of-the-art ways to use the CGM information, including “time in range” metrics of when glucose levels reach target levels and an ambulatory glucose profile report that organizes data into a usable display.

Beyond Hemoglobin A1c

“We’ve been living in an A1c world since 1993, the year the Diabetes Control and Complications Control Trial results were announced,” says Richard M. Bergenstal, MD, executive director of the International Diabetes Center at Park Nicollet in Minneapolis and a member of the consensus group. “But A1c has never been a very good individual care metric. It misses lows and variabilities in glucose. In this age of personalized medicine, we finally have the tools [through CGMs] that make it possible to know where your highs and lows are.”

 “A1c has never been a very good individual care metric. It misses lows and variabilities in glucose. In this age of personalized medicine, we finally have the tools [through CGMs] that make it possible to know where your highs and lows are.” – Richard M. Bergenstal, MD, Executive Director, International Diabetes Center at Park Nicollet, Minneapolis, Minnesota

Hemoglobin A1c is an average, so a benign-appearing measurement could mask the danger that a patient is spending considerable time in hypoglycemia and hyperglycemia outside the desired glucose ranges.

But until now there has been little guidance or agreement on the ranges to aim for and how much of their time patients should aim to spend within their range.

“Our group believes that clear, easy-to-understand, and broadly agreed-upon glycemic targets for time-in-range levels will positively impact short- and long-term diabetes outcomes, particularly if understood and adopted by people with diabetes,” says Tadej Battelino, MD, PhD, head of the Department of Pediatric and Adolescent Endocrinology at Ljubljana University Medical Centre in Slovenia and lead author of the report. “It is critical for clinical care, regulatory oversight, and research efforts related to CGM to all agree on standard core CGM metrics.”

Specific Goals and Metrics

The report provides the specific metrics patients and providers can use to work toward improving glycemic control. The group defines the target glucose range that most type 1 or type 2 diabetes patients should aim for as 70 – 180 mg/dL and 63 – 140 mg/dL during pregnancy.

The guideline recommends that patients aim to achieve at least 70% of their time in range — which converts to just under 17 hours of a 24-hour day. Patients should aim to spend less than 4% (58 minutes) below 70 mg/dL, less than 1% (14 minutes) below 54 mg/dL, less than 25% (6 hours) above 180 mg/dL, and less than 5% (1 hour, 12 minutes) above 250 mg/dL.

The guideline recommends more conservative targets for patients who are older or high-risk — with an aim to spend 50% or more of their time in target. These patients should be more focused on reducing the percentage of time spent in hypoglycemia — defined as less than 70 mg/dL — and preventing excessive hyperglycemia.

Time in Range and HbA1c Correspondence

The time-in-range percentages can be roughly translated into A1c levels, Battelino says: “On a population basis, the 70% time in range corresponds to an A1c of 7%,” which is the A1c target set by the American Diabetes Association for most patients. A 50% time in range corresponds roughly to an A1c of 8. The guideline notes that each incremental 5% increase in time in range is associated with clinically significant benefits for individuals with type 1 or type 2 diabetes.

Ambulatory Glucose Profiles

A characteristic that the time in range metric shares with hemoglobin A1c is that by itself it does not provide specific information on how to improve glycemic control. But the three components of an ambulatory glucose profile report — CGM metrics, summary glucose profile, and daily glucose profiles — provide the data in easily visualized ways to guide therapy recommendations.

The consensus statement recommends a standardized report to organize the data in a way that it is easy to interpret and act on — such as the ambulatory glucose profile, a format endorsed in the recently updated 2019 American Diabetes Association standards of medical care in diabetes.

“If your time in range is not good, you look at the profile picture. It shows when you are low and where you are high. It tells you not only that you need to take action, it tells you what action should be taken.” – Tadej Battelino, MD, PhD, Head, Department of Pediatric and Adolescent Endocrinology, Ljubljana University Medical Centre, Slovenia

The ambulatory glucose profile shows percentage of time within the target range or 70–180 mg/dL, below 70 mg/dL, below 54 mg/dL, above 180 mg/dL, and above 250 mg/dL. One part — the daily glucose profile — displays a graph of the glucose readings from a midnight-to-midnight period, highlighting the times of day when the glucose level goes above or below the target range. It’s easy to spot which hours of each day a patient is in range, above range, and below range.

“If your time in range is not good, you look at the profile picture,” Bergenstal says. “It shows when you are low and where you are high. It tells you not only that you need to take action, it tells you what action should be taken.”

Bergenstal reviews these reports with patients to identify specific ways to improve their control: “I like to say in clinic, ‘Why don’t we work on your post-dinner blood sugars and see what can we do about it — is it a medication adjustment, is it a lifestyle adjustment, is it exercise?’ And then at the next visit, it may be better, but another problem might pop up somewhere else. Our goal is constantly trying to get the glucose profile a little flatter, a little bit narrower, and mostly in target range.”

All the major CGM devices have an ambulatory glucose profile report option to upload data to create these displays.

The consensus statement was created by an international panel of 43 physicians, researchers, and diabetes patients convened by the Advanced Technologies and Treatments for Diabetes Congress in February. The recommendations have been endorsed by a variety of organizations, including the American Diabetes Association and the European Association for the Study of Diabetes. Although several Endocrine Society members took part, the fast turnaround time from the drafting to publication did not allow enough time for the Society to complete a formal review.

Seaborg is a freelance writer based in Charlottesville, Va. He wrote about the quest for accurate pediatric reference ranges in the October issue.

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