Is Time in Range More Important Than A1C?

The A1C test has long been considered the gold standard for measuring diabetes management success. But now, continuous glucose monitoring (CGM) technology provides a new measurement option for people with diabetes: time in range (TIR).

Experts say that both measurements have a role to play in successful diabetes management.

“Time in range reveals how much of the day a person’s blood sugar stays in the so-called ‘healthy zone.’ It’s measured using a continuous glucose monitor device,” says Mihail Zilbermint, MD, associate professor of medicine at Johns Hopkins University School of Medicine and chief of the division of endocrinology, diabetes, and metabolism at Suburban Hospital in Maryland.

“There may be different target ranges for certain populations,” says pediatric endocrinologist Kristin Arcara, MD, clinical codirector of the division of pediatric endocrinology and diabetes at Johns Hopkins Children’s Center in Baltimore. “For example, target ranges for patients who are pregnant [may be different],” she says.

Advantages

TIR can show what’s really happening from day to day, says Dr. Zilbermint. “It’s not just an average like A1C. It can help capture high sugar, low sugar, [and] glucose swings, which we know affect how people feel, function, and stay safe,” he says.

Dr. Arcara says that time in range can really help providers home in on treatment decisions — for instance, if they see that a patient’s blood sugar is high at a particular time of day. “Time in range really has a lot of advantages in clinical decision-making about insulin doses and medication doses,” she says.

TIR hasn’t been studied as extensively as A1C because it hasn’t been available for nearly as long. Nevertheless, preliminary data suggests that higher TIR is associated with better diabetes outcomes, including decreased risk of:

• Cerebrovascular accidents and microvascular complications

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• Diabetic retinopathy

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• Severe low blood sugar

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• All-cause mortality and cardiovascular disease mortality

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• Pregnancy-related complications

  [8]

Disadvantages

There’s no TIR without a CGM. “Pretty much the only way to get a time in range [measurement] is to have lots of data, so it requires people to wear continuous glucose monitors, or CGMs,” says Zilbermint. “We know that it’s not accessible or may not be appealing to everyone.”

Acara also says that TIR can be an issue if a patient’s not wearing the sensor continuously. “When you look at the time in range data, you get a picture of what their glycemic control is while they’re wearing their CGM, but it’s not going to pick up their glycemic control during those times when they’re not wearing the sensor,” she says. Not everyone loves wearing a CGM all the time: Frequent alarms, alerts, and reminders from CGM devices can also lead to diabetes tech distress and burnout.

Advantages

Diabetes experts trust A1C because generations of experiments have proven its value in assessing the long-term health risks of people with diabetes.

Disadvantages

Zilbermint uses both in his practice. “I don’t think it’s [an] either-or choice,” he says. “A1C [and] time in range answer different questions. A1C is like a semester GPA, and time in range is [like] a daily report card.”

TIR can better guide real-time treatment decisions, says Zilbermint. “I can look quickly at time in range, especially focusing on low blood sugars, because those are the dangerous situations ... while the A1C helps me confirm that I’m moving in the right direction with my patient.”

Arcara agrees. “Each has their strengths and limitations, and I would say they can be used in a complementary fashion,” she says.

Arcara also says that TIR is probably the most useful metric for making decisions about overall treatment strategy. “Time in range can give you a lot more granular data about the day-to-day,” she says. “You can look at the graph of what the blood sugars are doing throughout the day, and that can really guide you to make clinical decisions.”

• While the A1C test remains the gold standard for measuring average blood sugar, time in range has emerged as a vital metric that tracks the percentage of time your blood sugar stays within your target zone.
• Unlike A1C, which can hide dangerous blood sugar swings, TIR provides granular data that helps healthcare providers identify specific times of day when blood sugar is high or low to better adjust insulin and medication doses.
• A1C is backed by decades of research linking it to long-term health outcomes and doesn’t require wearable tech; TIR offers immediate feedback but requires consistent use of CGM devices.
• Medical experts generally prefer to use both metrics together, viewing A1C as a “semester GPA” that confirms long-term progress and TIR as a “daily report card” used to guide immediate clinical decisions and help improve quality of life.