When your blood sugar is in the target range, it provides information about the effectiveness of your diabetes therapy. In this article you will learn everything you need to know about this indicator and why the Time in Range (TIR) outshines the former gold standard HbA1c (A1c).
As long as I can remember, the HbA1c value was used as a gold star measuring stick in judging overall blood sugar control. If an A1c was below 7%, most endocrinologists were satisfied.
However, with the increased use of continuous glucose monitors (CGM), additional data has allowed providers to now see a broader picture of how well-managed their patients’ blood glucose levels are. This is the value of Time In Range, or TIR for short.
1. What does Time in Range mean?
Time in Range (TIR) indicates the percentage of how long your glucose value was within the target range during a defined period. This number can sometimes be described as “hours in target range” as well. If a person has a TIR of 50%, that would indicate that your glucose levels were within the target range for approximately 12 hours on any given day.
Target range may vary from person to person, as best guided by your primary care provider, but most official recommendations range from 70 mg / dl to 180 mg / dl (3.9-10 mmol / l).
2. Why is Time in Range so important?
In contrast to the HbA1c value, the Time in Range offers a few decisive advantages. Primarily, the A1c only represents the average glucose value over the past 2 to 3 months as a single snapshot. It is devoid of any additional data or explanations. Mapping the high's and low's, via TIR, offers a fuller view of the day-to-day management for a person with diabetes.
Here is a small illustration:
Although all three people received a supposedly good Hb1Ac from their doctor, a closer look at the times inside and outside the target area shows a different picture with regard to the variability of the glucose values. This information is vital in making those small, and sometimes constant, changes needed to live well with diabetes.
And just in case we needed more proof of concept, we now know that it’s not only permanently elevated BGs that risk long-term complications, but also fluctuating glucose levels. The more fluctuations over time, the more risk towards complications such as diabetic retinopathy or diabetic kidney disease.
3. Relationship between TIR and risk of complications confirmed in studies
Scientists found that there is a strong connection between the time in range and the risk of secondary diseases. Some scientists even believe that TIR is the superior indicator of complications. The HbA1c is an indirect measurement of glucose in the blood, and is dependent on the renewal of the red blood cells which can vary from person to person. This makes the A1c a measure that can be influenced by various external factors.
As such, many are leaning towards the simplicity of TIR. The higher the time in the range percentage, the lower the risk of developing complications. The lower the TIR, the higher the glucose variability and thus the risk of possible complications.
Brief sidebar for anyone who needs a diabetes 101 educational reminder:
The HbA1c shows the percentage of the “sugared” red blood pigment in the total hemoglobin content in your blood. Or, to put it simply, the sugar in your blood adheres to the red blood pigment (hemoglobin) a bit like cake frosting. This ‘frosting’ sticks as long as the red blood cells survive. Survival is an average of 8-12 weeks, but can vary from person to person.
Another great thing about the Time in Range value is that you can figure it out yourself! If you are a user of a continuous glucose monitoring at home, you do not have to go to a doctor or to a laboratory as you would with the HbA1c value. This, in conjunction with advances in telemedicine, makes the TIR an ideal part of your diabetic toolbox.
4. What is the optimal time in range target?
Most experts agree that the standard target range of 70-180 mg / dl (3.9-10 mmol / l) is best. However, factors such as pregnancy, hypoglycemia, or other health conditions may require individual adjustment of the target range on a temporary or ongoing basis. The target range should be determined individually by your doctor. Once you do set your range, aim to be in that target range as much as possible while actively avoiding hypoglycemia.
According to studies, the average time in range in people with diabetes is typically around 50% to 60%. Based on the latest findings, Researchers at the ATTD Congress 2019 (Advanced Technologies & Treatments for Diabetes) made the following recommendations for people with type 1 and type 2 diabetes:
- At least 70% of the day within 70 to 180 mg / dl (3.9-10 mmol / l)
- Less than 4% of the day below 70 mg / dl (3.9 mmol / l)
- Reduction of time over 180 mg / dl (10 mmol / l) per day
Most importantly, one should take care to set small but achievable goals. If measuring TIR is new for you, start with aiming for 1 hour in the target area per day. Slowly increase the time in range by 5% overtime. And utilize any telemedicine options available to stay in close contact with your primary provider.
And just in case you ever wondered what the normal TIR is for a person without diabetes, a recent study figured that out. In the study*, people without diabetes were monitored for 10 days with CGM systems.
Result: 97% time in range with a target range of 70 to 140 mg / dl (3.9-7.8 mmol / l) and an average glucose value of 99 mg / dl (5.5 mmol / l) with only slight variation. Welcome to your new favorite factoid!
5. How do I measure time in the target range?
In order to determine your personal time in range, you need your glucose data, which would be measured with a glucose sensor in the previous 14 days. If you are using a CGM system, the work is done for you since the CGM systems determine a glucose value around the clock giving you a consistent stream of measured values on average every 5 minutes.
Furthermore, most CGM (or other Flash Glucose Monitoring) systems automatically determine the time in the range and make this information readily available to you either on the reader, on an app, or in the respective evaluation software.
With a standard blood glucose meter, using individual fingersticks, the endeavor is unfortunately more complex. In order to obtain a similarly consistent database, you would have to determine each data point by pricking your finger every 5 minutes. To be truly consistent, you would need to keep up this effort through the night as well. It’s worth noting that we do not encourage this level of commitment because there is not enough coffee in the world and you’d be crazy-cakes-exhausted by the end of it all.
For those brave caffeine-addicted warriors who feel dedicated enough to try this level of insanity, the TIR can be manually calculated as follows:
(Values in target area / total amount of values) x 100 = amount of values in target area in %.
In the mySugr app, you can define your individual target area in the settings and have it displayed in the blood sugar graph on the home screen. The target area you defined is a little darker. So you can see at a glance how the day is developing in terms of time in range.
How do I use the Time in Range to optimize therapy?
While you should always discuss therapy adjustments with your diabetes care provider in advance before making any changes, Time in Range has proved to be an ideal monitor for your diabetes therapy. Use it to check if changes to your therapy have the desired effect, such as:
● You notice that your carbohydrate factor is somehow off. You can contact your diabetes team and make a quick adjustment. After 14 days, you look at your time in range and find that this little tweak has increased your TIR by 3%!
● You struggle with high BG values after a meal and you suspect the pre-meal bolus as the culprit. Reach out to your care provider and discuss adjusting that preprandial time. In a week or so, view the TIR percentage to determine whether you are on the right path!
The Time in Range gives you information about whether your efforts are going in the right direction in a short amount of time. No more waiting for the next appointment with the doctor to look forward to your HbA1c value.
Again, small adjustments. You should do this in a structured manner and coordinate all steps with your diabetes team. This is the only way the Time in Range value can develop its superpower.