For decades, diabetes doctors, educators, and patients have all known one simple fact: High blood sugar over time is bad news. It can lower both the quality and quantity of life. The science on that is irrefutable. But figuring out how to measure it, and what constitutes “good” or “poor” blood sugar control, has been a larger problem.

We’ve gone from crude urine tests that only told us what our sugar levels were hours before, to fingerstick tests that only told us what our sugar was in that very second, to a lab test called the A1C that provides a 3-month measure, but still only a hazy view of what is, in reality, a devilishly complex picture.

But now there’s a new way of looking at blood sugar called Time in Range, or TIR. It’s the next big thing, perhaps the biggest thing ever when it comes to blood sugar measurement. We’ve got the scoop on everything you need to know about it.

TIR basically moves away from a single precise measurement of blood sugar (or blood glucose, as it’s known medically), to give people a sense of how often they are staying within the desired healthy range (roughly 70-180 mg/dL).

It uses continuous glucose monitor (CGM) data to “count” the actual amount of time each day a person with diabetes (PWD) stays within those desired control limits, expressed in average hours and minutes over any period of days, weeks, or months.

That’s very different from the traditional “gold standard” measurement of blood glucose control that most PWDs are familiar with, the A1C test. That test, in fact, only provides an average of blood sugar levels over the previous 3 months — which is poor at reflecting change and does not measure variability. That means a “good” A1C result of 6 to 7 percent could be nothing more than a midpoint between severe daily high and low blood sugars over several months.

This is a problem, as increasing research shows that variability may play nearly as large a part in poor diabetes outcomes as do the sugar levels themselves.

TIR, on the other hand, reflects the number of actual hours that a PWD remains in healthy blood glucose range over a given period.

Adam Brown, a type 1 diabetes advocate now serving as Market Access Program Manager for the nonprofit diabetes data company Tidepool, credits a JDRF clinical trial from 2008 for “putting CGM on the map,” which ultimately lead to a push for recognizing and using TIR.

Diabetes advocates fed up with the emphasis on A1C that was so oblivious to quality-of-life concerns, started a campaign called Beyond A1C. That was led by the diaTribe Foundation, where Brown worked at the time.

It explained the limitations of the A1C as a one-size-fits-all metric: “It cannot capture other critical outcomes that matter to people with diabetes on a daily basis. Low blood sugar (hypoglycemia) can be fatal, and yet, A1C tells us nothing about it. New therapies may dramatically improve quality of life, but those improvements won’t necessarily show up in an A1C value. Two people can have the exact same A1C value but spend wildly different amounts of time at high and low blood glucose values.”

Beyond A1C called for a new approach: “Given recent improvements in the accuracy of glucose sensing devices, our metrics must reflect the additional data that glucose monitoring provides.”

Validation of TIR as an accepted outcome measure by the medical establishment was a long haul, one that included improved technology from companies like Abbott, Dexcom, and Medtronic; new clinical research; and meetings between the Food and Drug Administration (FDA), medical professionals, and PWDs that resulted in international consensus. By 2019, the American Diabetes Association’s (ADA) Standards of Care included TIR goals for the first time.

The current ADA Standards bundle TIR with two other closely related metrics: Time Below Range (TBR) and Time Above Range (TAR). These three metrics together form a risk picture more complete than A1C or any other previous measures can. In their Standards document, the ADA writes, “The primary goal for effective and safe glucose control is to increase the TIR while reducing the TBR.”

In other words, max-out time in the healthy (and happy) range without glucose lows.

What exactly is the happy range for TIR? It depends on whether you live with type 1 or type 2 diabetes. Plus your age. Oh, and are you pregnant? And even with these overarching categories, the ADA favors targets “personalized to meet the needs of each individual with diabetes,” but for most people, the goal is a TIR of 70 percent of the time between the blood sugar levels of 70-180 mg/dL, which corresponds to an old fashioned A1C result of 7 percent.

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The ADA isn’t standing alone. Their new goals have been endorsed by the American Association of Clinical Endocrinologists (AACE) and by the European Association for the Study of Diabetes (EASD), among other medical organizations.

Meanwhile, the JDRF is keeping TIR on the map and continuing to spread the word. Dr. Aaron Kowalski, the organization’s CEO, says, “The ability to measure Time in Range with continuous glucose monitors has been transformative for type 1 diabetes.” He says the organization now integrates it “into all aspects” of their activities, including “research, drug and medical device development, and clinical care and education.”

All that said, it’s still difficult to gauge how widely physicians have adopted TIR in clinical practice, especially at the primary care level, where most diabetes treatment takes place. If the past model of A1C is any guide, we probably won’t see widespread use of TIR as the guiding number for therapy design, implementation, and refinement until TIR is widely adopted by the big health insurance companies (aka payors).

Meanwhile, just as diabetes educators (now officially called Diabetes Care and Education Specialists) have historically used A1C and glucometer data to help PWDs understand how their diabetes control stacks up, many are now adopting TIR.

The newly renamed Association of Diabetes Care & Education Specialists (ADCES) offers training courses on the subject and keeps its members current on the growing use of TIR as a possible standard benchmark through various articles in their publications.

But regardless of how long it may take doctors and educators to embrace this measure, PWDs can use — and are using — TIR in their daily lives right now.

Frank Westermann, one of the founders of the diabetes data platform mySugr, says, “The great thing about TIR is its simplicity. As a PWD you know the ‘healthy’ ranges and it’s a simple concept to communicate that you are just as healthy as a normal person when you are within these ranges. Also, it’s a real-time indicator that all of us can just look up,” rather than waiting for an A1C result four times per year. On that last point, Westermann praises what he calls a shorter “feedback loop” provided by TIR.

PWDs can readily check out their TIR on their CGM software without the need to go to their doctors’ offices. It’s front and center in Dexcom’s CLARITY mobile app, smack in the middle of the Medtronic CareLink Assessment and Progress Report, present on the dashboard of the Tandem t:connect app, and is featured on many third-party D-apps like mySugr.

Can’t be bothered to look at a report? Dexcom’s system can text you a weekly update on your TIR, complete with a note on how it has changed from the week before.

Speaking of reports, how does TIR differ from the Ambulatory Glucose Profile (AGP)? The AGP is an attempt at an industry standard for presenting CGM data for both clinicians and PWDs. There’s quite a bit of information in an AGP report, including — at the top right — a TIR graph. So TIR is part and parcel of AGP, not a replacement for it.

Dr. Roy Beck, the director of the Jaeb Center for Health Research Foundation, says, “TIR seems to resonate with people with diabetes more so than mean glucose or time above range.”

He thinks that the fact that TIR is expressed as a percentage of time makes the data “more intuitively understandable” than previous measurements of blood sugar control, and that people like the positive message that increases in TIR are a good thing — rather than struggling with the decades-old mission of eternally seeking lower numbers.

Meanwhile, advocate and D-technology expert Brown likes the way TIR can be self-deployed. “I think about TIR as a way to answer ‘What is working in my diabetes? What is not working? What should be changed? Did the change I just made actually have an impact?’ Because you can measure TIR over any time horizon, it is far better suited to answering these kinds of questions than A1C.”

Diabetes advocate, writer, and long-term type 1 Kelly Kunik agrees. She says, “TIR has been a gamechanger for me.” She uses an Omnipod tubeless pump, a Dexcom G6 CGM, and a host of supporting data-tracking tech including Glooko and CLARITY. She challenged herself to meet the ADA goals of 70 percent TIR for 99 days following a period of longterm A1C creep. At the start of the challenge, her TIR for the previous 3 months was 57 percent.

She says that she worked hand-in-hand with her medical team throughout the challenge, uploading data, and making changes to her pump settings. In the beginning, Kunik checked her TIR “almost daily,” and used the data to make what she calls “dietary tweaks.”

Kunik says that during the process she “celebrated” each percentage point improvement, but was careful not to beat herself up if she had a period when she didn’t improve. Still, she confesses that days outside of range were annoying and that sometimes she was even “downright pissed.”

“But I realized that the days where my blood sugar graph was full-on wonky were occurring less often,” says Kunik. Her positive mindset helped her avoid one of the largest potential land mines of TIR: Focusing on the stick, not the carrot.

In a study published in the journal Clinical Diabetes in spring 2018, researchers found “survey respondents tended to perceive greater therapy success in preventing negative time-in-range outcomes than in delivering positive time-in-range outcomes.”

How did it work out for Kunik on her 99-day plan? She reported that by focusing on TIR, she improved it from 57 to 84 percent, with only 1 percent in that TBR low range. Her old fashioned A1C dropped enough to make her endocrinologist smile. Kunik says that, for her, “Focusing on TIR one day at a time is a lot easier than focusing on a good A1C for 3 months.”

So, will TIR actually replace A1C in the future? Brown thinks so, saying, “It should replace A1C! For me, the only question is when.” In his mind, TIR does “everything A1C does” plus “all the other additional awesome and highly important metrics.”

He does see some speed bumps to widespread adoption though, the largest being the lack of “broad CGM access to everyone with diabetes,” including type 1s, type 2s, and even people with prediabetes.

No CGM, no TIR. You need the former to get the latter.

Other speed bumps Brown sees include the need for more clinical education and more research. He’d like to see studies on the health economics of TIR, saying, “How much does improving TIR save in terms of healthcare costs? What is the annual healthcare cost of someone with a TIR of 60 percent vs.70 percent? How much should our system pay for X percentage improvement in TIR?” He also wonders what levels of TIR will associate with improved longterm health outcomes.

Meanwhile, the traditional A1C test requires either a blood draw at a lab or a fingerstick test at a clinical location. In this time of COVID-19, with PWDs being at higher risk of serious illness if they contract the virus, many are reluctant to come into clinical locations for their quarterly A1C test, and many doctors are reluctant to have their diabetes patients go into medical environments as well.

Enter TIR as “the Zoom Meeting of diabetes control tests.” CGM data can be safely uploaded remotely, giving both PWDs and their medical teams a zero-contact way of measuring diabetes control. Just as the virus has rapidly forced many changes on society, so too, may it accelerate the adoption of TIR over A1C.

Kunik, now six months out from her original 99-day challenge, continues to focus on TIR. She says that while the “weight of [diabetes] knowledge gets incredibly heavy to carry,” she finds TIR “less overwhelming” for her to process than other approaches to diabetes control, and that it integrates better into her real life.

“I’m taking it one day, one daily TIR, at a time,” says Kunik, “because it’s working for me.”