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Time in Range

Article By Carolien Koreneff, CDE-RN, FADEA

Monitoring Time In Range can offer an opportunity for people with diabetes to improve the management of their diabetes, whilst reducing the risk of developing diabetes related complications.

What is Time in Range?

The Time in Range (TIR) is the percentage of time a person with diabetes spends with their sensor glucose (SG) levels in a particular target range. TIR can also be reflected as the hours per day spent in range.

What this range is will vary from person to person; for people who use continuous glucose monitoring (CGM) it is generally recommended to aim for SG levels between 3.9-10 mmol/L, while reducing time spend in hypoglycaemia.

Click image to enlarge.

Figure 1; CGM-based targets for different diabetes populations.2

 

TIR was validated as an outcome measure for clinical trials complementing other components of glycaemic control, like blood glucose and HbA1c.1  Numerous studies have demonstrated significant clinical benefits of CGM use in people with diabetes regardless of insulin delivery method.  The International Consensus in Time in Range was released in 2019.2

The metric developed by the International Consensus group includes three key CGM measurements: percentage of readings and time per day within target glucose range (TIR), time below target glucose range (TBR), and time above target glucose range (TAR). The primary goal for effective and safe glucose control is to increase the TIR whilst reducing the TBR.

 

Is TIR the same as the HbA1c?

Although relationships between TIR and HbA1c have been witnessed, they are not the same. Analyses or data from four clinical trials showed that TIR of 70% corresponded strongly with an HbA1c of 7% (53 mmol/mol) and TIR of 50% corresponded with an HbA1c of 8% (64 mmol/mol). Similarly, an increase of TIR of 10% (2.4 hours per day) corresponds to a decrease in HbA1c of around 0.5% (5.0 mmol/mol).3

TIR and HbA1c are not efficient for estimating the time in hypoglycaemia, so composite metrics (TIR+ TBR) are suggested to be complementary to HbA1c.4  However, higher percentages of TIR, similar to lower HbA1c results, are associated with a decreased risk of the development of diabetes related complications.

 

Limitations of HbA1c

It is recognised that, whilst HbA1c reflects average glucose over the last 3 months, there are limitations.  One limitation of HbA1c is the lack of information about acute glycaemic excursions. HbA1c does not show how much hypo- and hyperglycaemia a person had and it fails to identify the frequency and extent of intra- and interday glucose variation.2, 5  To put this in simpler language: one can have an HbA1c of 6.5% if BGLs are consistently between 4 and 8 mmol/L, but one can also have an HbA1c of 6.5% with BGLs between 2 and 22 mmol/L.

HbA1c is a weighted average of glucose levels, meaning that glucose levels in the past 30 days contribute substantially more to the level of HbA1c than do glucose levels from 90-120 days earlier. It is also important to note that amongst other things, anaemia, haemoglobinopathies, iron deficiency and pregnancy can affect HbA1c measures. The HbA1c test therefore can, at times, fail to accurately reflect the average or mean glucose.

 

Limitations of TIR

The use of CGM greatly increases the ability to assess glycaemic control throughout the day, as it allows for the direct observation of glucose excursions and daily profiles, including patterns of hypo- or hyperglycaemia, which can help in making therapy decisions and/or lifestyle modifications. However, CGM would need to be actively used in order to be effective which can be costly, and there may be a delay in registering SG changes in dynamic situations.

CGM is not a “set and forget” system, but requires the user to interpret the data and act upon this appropriately.

 

What is the optimal Time In Range target?

As outlined above, most experts agree that a target range of 3.9-10.0 mmol/L is ideal. However special considerations, such as pregnancy or other health conditions, will need to be considered (see figure 1.).

In short it is recommended to spend;

  • Less than 4% of the day in TBR (<3.9 mmol/L)
    • And less than 1% of the day <3.0 mmol/L
  • At least 70% of the day TIR (3.9-10.0 mmol/L)
  • Less time in TAR (>10.0 mmol/L)

 

How can the TIR be improved?

The first priority is always to reduce TBR to target levels and then to address TIR (or TAR) targets. Achieving targets for both TBR and TIR will reduce time spend in TAR. Some clinicians may choose to target the reduction of the high glucose values (TAR) and minimise hypoglycaemia (TBR), thereby arriving at more time in the target range.

To improve TIR it is important that the person with diabetes actively and accurately counts carbohydrates and adjusts bolus (pre-meal) insulin doses based on the current SG or BG level, their insulin to carbohydrate ratio (ICR), insulin sensitivity factor (ISF), insulin left on board (IOB) and insulin action/duration. Physical activity and meal composition of course also play a major role.

As people with type 2 diabetes tend to have less glucose variability and less hypoglycaemia than those with type 1 diabetes, people with type 2 diabetes can often achieve more TIR, more easily.

When it comes to making insulin dose adjustments; slow and steady wins the race.

 

References:

  1. Andrade Lima Gabbay et al, Diabetology & Metabolic Syndrome, published 16 March 2020; Time in range: a new parameter to evaluate blood glucose control in patients with diabetes. https://dmsjournal.biomedcentral.com/articles/10.1186/s13098-020-00529-z
  2. Battelino et al, Diabetes Care, August 2019; Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. https://care.diabetesjournals.org/content/42/8/1593
  1. R. W. Becket al, J Diabetes Sci Technol. 13 January 2019; The relationships between time in range, hyperglycemia metrics, and HbA1c. https://pubmed.ncbi.nlm.nih.gov/30636519/
  2. R. A. Vigersky, C. McMahon, Diabetes Technology & Therapeutics, online 1 February 2019; The Relationship of Hemoglobin A1C to Time-in-Range in Patients with Diabetes.  https://www.liebertpub.com/doi/full/10.1089/dia.2018.0310
  3. T. Danne et al, Diabetes Care December 2017; International Consensus on Use of Continuous Glucose Monitoring. https://care.diabetesjournals.org/content/40/12/1631