How Time in Range Changed My View of Diabetes
We all have heard of A1C and how it reports an overall average of glucose levels for the past 3 months.1
But have you heard of time in range (TIR) and how it reports what percentage of time glucose levels were within target range?
A1C and time in range: what's the difference?
A1C
A1C sums up glucose levels in a single number. It doesn't reflect how much those levels varied over time. The same A1C can result from having glucose readings that were consistently within a narrow range or from a mix of high, low, and in-range readings that vary widely. There's no way of knowing the difference without looking at all of the readings captured over time.2,3
Time in range
This is where time in range comes in. TIR reports glucose levels in a way that provides a view of how much time glucose levels were within, above, and below the targeted range of readings.1
TIR is expressed as a percentage of time per day. For example, 70 percent in-range translates into glucose levels that remained between 70 and 180 mg/dL (or between 3.9 and 10 mmol/L) at the rate of 17 hours throughout a 24-hour day. With this kind of reporting, TIR gives us some sense of how stable glucose levels have been.1,4
Time in range and its impact on me
When I started looking at my time in range, I felt a shift in how I thought about my glucose level readings. Instead of focusing on a single reading, I found myself considering my readings in a wider context.
It was like taking a deep, relaxing breath. I got a sense of how I was managing my diabetes overall – not just at one particular point in time. It was the difference between focusing on a single item (and probably giving it too much importance) and seeing the bigger picture.
By looking at TIR, I could see that my glucose levels were in range during the vast majority of time. At the same time, I could still see how much of the time my glucose levels were high or low.
With TIR, the highs and lows looked more like blips on my radar instead of major events. With this perspective, I feel a sense of calm and confidence about how I am managing my diabetes.
Why is time in range an important measurement?
For as long as A1C has been recognized as a way to measure long-term glucose management, it has also presented a dilemma to doctors and scientists. This led researchers to reexamine the thinking behind A1C and uncover a blind spot. Because the same A1C can result from vastly different sets of glucose level readings, it doesn’t report on how much time glucose readings are in-range, high, or low. TIR provides more actionable data than A1C alone.4
Providing a complete picture
Being able to measure time along with levels gives a more complete picture of how well a person is managing their diabetes. While TIR goals can be influenced by a person's unique situation, there are some standard recommendations.
The standard recommendations for TIR are:5
- At least 70 percent of the day in range
- Less than 4 percent of the day below target range
- Minimize the amount of time above target range
How is time in range measured?
With a continuous glucose monitor
TIR is determined by analyzing at least 2 weeks of glucose level readings by grouping how many of the readings are in range (between 70 and 180 mg/dL), above (above 180 mg/dL), and below (below 70 mg/dL). Then the number of readings in each group is divided by the total number of readings to calculate the percentage of time spent in each group.1,6
Continuous glucose monitors (CGMs) are well-suited for determining TIR. With a CGM, glucose levels are measured every few minutes continually around the clock. This amount and spread of readings means that the TIR reported in the CGMs app provides a more complete picture of glucose levels.1,5
With a glucometer
You can also get a sense of TIR using a glucometer, but it takes more work and will be less accurate than with a CGM.1
To calculate TIR using a glucometer, start with at least 2 weeks of glucose level readings spread across each day. Basically, check your blood sugars often – fasting, before and after meals, and bedtime. Most apps that pair with a glucometer will include a line graph that shows how the captured glucose readings change over time.6
If your glucometer doesn't have an app, you can calculate your TIR manually by doing the following:7
- # of blood sugars in range / # of blood sugars checked x 100 = TIR
Because there are fewer readings taken with a glucometer and checks tend to drop off while sleeping, the resulting TIR report will be less complete and accurate.
A clearer view of my diabetes management
Using TIR gives me a more accurate read on what my glucose levels are doing over time. Learning that I'm staying in range most of the time has made me more confident about how I am managing my diabetes.
As a result, I'm less bothered by the times my reading is high or low. That doesn't mean I ignore them – it means that I respond to them with the appropriate amount of attention.
Have you tried looking at your time in range?
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