Is it time for a new metric for diabetes monitoring?

By Naveed Saleh, MD, MS | Medically reviewed by Kristen Fuller, MD
Published September 23, 2022

Key Takeaways

  • Although hemoglobin A1C levels are widely used to assess diabetes over a 3-month period, they fail to capture the disease’s immediate impact.

  • Time in range (TIR) refers to the percentage of readings and time per day in target glucose range and has been correlated with improved clinical outcomes. It’s recommended as an adjunct measure to A1C to help guide diabetes interventions.

  • Clinicians should be aware of TIR when treating diabetes patients; endocrinologists and primary care physicians should consider using the metric to provide optimal care.

Diabetes treatment has advanced rapidly during the past 30 years—but the inability of hemoglobin A1C to contain its more granular impact could be undermining efforts to care for the disease.

Currently, A1C levels drive decision-making including regulatory approval, medication choice, and reimbursements. But experts are promoting a complementary metric, TIR, to advance patient care and self-management.[]

Why A1C falls short

Although A1C drives treatment decisions and is a primary outcome in trials of diabetes agents, it only tracks mean glucose during the past 2–3 months.

It doesn’t provide information on acute glycemic excursions, or acute complications of hypoglycemia or hyperglycemia. It also doesn’t reflect variations in glucose levels that occur during the day or between individual days.

Another issue is that some conditions, such as pregnancy, anemia, or iron deficiency can interfere with A1C measures. In some patients, A1C can fail to recapitulate average glucose levels even when no disease is present.

Origins of TIR

Continuous glucose monitoring (CGM) has made it possible to observe daily glucose profiles and glycemic excursions. CGM devices help you manage Type 1 or Type 2 diabetes with fewer fingerstick tests. A sensor just under your skin measures your glucose levels 24 hours a day.

A transmitter sends results to a wearable device or cell phone. It takes time to learn how to use CGM, but this granular data can help guide immediate therapy and lifestyle changes. One issue with CGM, however, is that the patient must be actively involved; they need to interpret and act on the data.

CGM is most beneficial with high-risk patients or those with severe hypoglycemia, as well as those with limited awareness of hypoglycemia.

It can help guide the use of multiple daily injections of insulin or subcutaneous insulin transfusion.[]

Although core CGM metrics offer valuable information, they can be difficult to interpret, so a consensus metric titled “times in range” was proposed at the 2017 Advanced Technologies & Treatments for Diabetes (ATTD) conference. The ATTD and others promote the use of TIR in conjunction with A1C to provide actionable information.

“The panel agreed that establishing target percentages of time in the various glycemic ranges with the ability to adjust the percentage cut points to address the specific needs of special diabetes populations (eg, pregnancy, high-risk) would facilitate safe and effective therapeutic decision making within the parameters of the established glycemic goals,” wrote the authors of an International Consensus Report published in Diabetes Care.[]

TIR captures three key measures: 1) percentage of readings and time per day in target glucose range (TIR); 2) time above target glucose range (TAR); 3) and time below target glucose range (TBR). The goal is to boost TIR and decrease TBR.

Since the 2017 CGM consensus, various studies have supported TIR’s clinical utility. Researchers validated the importance of TIR using data from the Diabetes Control and Complications Trials, which popularized the clinical benefits of normal/near-normal blood glucose levels.

Other research has shown higher risk of severe retinopathy in patients with lower TIR.

Lower TIR has also been linked to carotid intima-media thickness, which represents microvascular changes. For children with diabetes, TIR correlates with A1C levels and could be a useful marker, per the literature.

TIR in clinical practice

According to a survey by US investigators published in Clinical Diabetes, patients desire a metric that they can follow that reflects more granular changes in glucose levels. The investigators aimed to assess patient perspectives regarding different diabetes treatments, including quality of life.

"Our results underscore the need to consider the full spectrum of patients’ daily glycemia rather than simply the 3-month average, as measured by A1C."

Runge, et al.

“’Time spent in the ideal blood glucose range’ was rated as having a ‘big impact’ by all three groups surveyed … and can be used to quantitatively evaluate treatment efficacy,” the authors added.

Intriguingly, about twice as many of respondents with type 1 diabetes thought TIR had a bigger impact on their lives than A1C levels.

The American Diabetes Association (ADA) also promotes the use of TIR in routine clinical practice and has developed an initiative that educates physicians on how to use the metric in routine clinical practice.[]

“Published data suggest a strong correlation between TIR and A1C, with a goal of 70% TIR aligning with an A1C of ∼7% in two prospective studies,” the ADA wrote. “The ADA’s Time in Range initiative will provide guidance on treating your patients with diabetes who might benefit from time in range.”

Here is a video on how primary-care physicians can leverage the power of TIR. Clinicians should consult such resources to stay apprised on the significance of TIR in treating their diabetes patients; primary care physicians and endocrinologists should consider utilizing it to care for such patients.

What this means for you

TIR is promoted as a complement to A1C levels, which serve as a long-term measure of diabetes status. The minute-to-minute measurements of CGM allow for clinicians and patients to make treatment decisions in real time. Clinicians should be aware of the importance of TIR in their diabetes patients, with endocrinologists and primary care physicians using the metric to provide optimal care.

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