For decades, the diabetes care community has been obsessed with three little characters: A-1-C. A1C, which is short for hemoglobin A1C, is a blood test that reflects a person’s average glucose level for the past eight to 12 weeks. Ever since the Diabetes Control and Complications Trial (DCCT) showed a relationship between A1C and the development of long-term diabetes complications, most research and clinical efforts have focused on A1C reduction. Unfortunately, the A1C has some serious limitations.
For one thing, there are many health conditions and blood abnormalities, such as anemia and iron deficiency, that influence the accuracy of the A1C. Additionally, obtaining an A1C isn’t the easiest thing to do: Measurement usually requires a blood draw at a lab (with several days’ wait time for the result) or a visit to a diabetes clinic that has special equipment for performing point-of-care A1C testing. But more importantly, A1C is not always a good reflection of the quality of glucose control. Those with frequent high and low glucose levels might have a decent A1C since their overall average isn’t too bad, but those wild glucose swings can affect one’s safety, performance, and daily quality of life. In the example below, Even Steven and Tillie McHilly have the same average (and same A1C), but Steven’s glucose levels are much more stable. Whose glucose control would you rather have?
What is time in range?
In recent years, a new statistical measurement (also called a “metric”) has gained popularity. Time in range, or TIR, represents the amount of time (usually expressed as a percentage) that your glucose is above a certain level and below a certain level. For example, if your target range is 70 mg/dl to 180 mg/dl, and your TIR is 55%, you are spending a little more than half of your time above 70 and below 180. Using the Even Steven and Tillie McHilly examples below (with their target range in gray), Steven spends about 90% of his time within the target glucose zone, while Tillie’s TIR is only about 30% — she spends most of her time above or below the target glucose zone.
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The fact that Tillie spends most of her time in a suboptimal glucose range does not show up in her A1C, but it is very clear from her TIR. Here’s the really cool part: TIR correlates very closely with the A1C, particularly when looking at data from two weeks or more. Recent research has shown that there is about a 0.5% A1C decrease for every 10% increase in time in range. So, time in-range not only provides a measure of glucose stability, but also serves as a predictor of long-term complication risk.
How does one learn their time in range?
Since we’re dealing with glucose values, there are two options for determining your TIR: Finger-stick (meter) readings and continuous glucose monitor (CGM) data. Some meters can calculate TIR by syncing with a smartphone app, downloading to a computer, or right on the meter itself. Essentially, the software takes the glucose values on the meter and determines the percentage that are within the target range. The problem with this approach is that meter readings don’t truly represent what is going on throughout the day and night. They are point-in-time values that are usually taken before meals, so they fail to capture what is happening after meals, between meals, and throughout the night.
CGM is tailor-made for generating TIR information. CGM generates data points every one to five minutes throughout the day and night, so the information is complete and unbiased. Some systems, such as the FreeStyle Libre CGMs, can produce TIR reports right on the receiver, while others, such as the Dexcom systems and Ascensia Diabetes Care’s Eversense, generate the data by syncing with a smartphone app. Still others, such as Medtronic’s Guardian Connect, allow the user to download to an online program.
Regardless of the system, it is best to use time blocks of seven days or more to generate TIR, as there can be a great deal of variability from one day to the next.
What should your target range be?
By now, it should be obvious that TIR is pretty boss. Which begs the question: “What should my target range be?” This is something that should be individualized and discussed with your health care team. A panel of experts at the Advanced Technologies & Treatments for Diabetes (ATTD) Congress developed a set of general guidelines that has been endorsed by most major diabetes organizations. Their recommendation for most people with type 1 or type 2 diabetes is to keep glucose levels within the range of 70 mg/dl to 180 mg/dl. However, it is reasonable to set looser targets (such as 80 mg/dl to 200 mg/dl) for the very young, very old, and those challenged by frequent/severe hypoglycemia. Tighter targets (such as 70 mg/dl to 150 mg/dl) are often used by those at low risk of hypoglycemia, as well as by folks who use automated insulin delivery systems. Even tighter targets (such as 60 mg/dl to 140 mg/dl) are commonly used during pregnancy.
How often do I need to be “in range”?
It is unreasonable to be within your target glucose range all the time. That would be like a baseball player expecting to get a hit every time they come up to bat. For most people, it is reasonable is to get a “hit” at least 70% of the time, with fewer than 4% of your time below your target range (each 1% represents about 15 minutes per day) and less than 25% above target. This represents fairly stable control without excessive glucose swings. Elderly people and those with hypoglycemia unawareness (in which a person does not experience the usual early warning symptoms of hypoglycemia) may aim for even less time below target and allow for more time above.
Of course, these goals need to be individualized. Rather than choosing an arbitrary goal, see where you are currently and try to improve over time. For example, if your current glucose average is well above where you want it to be and your TIR is very low (say 10%), set small achievable goals. Raising your TIR by 10% each month might be a reasonable goal. If your current TIR is high (85%) but you spend 8% of time below target, your goal might be to reduce the lows to 2% or 3% while maintaining at least 80% TIR.
How can you improve your time-in-range?
If you’re looking to up your TIR, here are some strategies that I’ve found very helpful:
Manage your carbs
Note, this doesn’t mean avoid carbs. Although carbs are the major contributor to postmeal rises in blood glucose, they are also an important source of energy and … well … quite delicious. You can include carbs in your diet and still manage your glucose nicely. Just make an effort to keep the carb portions modest and choose slower-digesting (low-glycemic-index) forms of carbohydrate whenever possible.
Use a CGM
Not only does a CGM help you to figure out your TIR, it can also help improve it. Set the high and low alerts at levels that provide valuable early warnings without being a major nuisance. And be sure to respond to the alerts with corrective action immediately. This will minimize the frequency, severity, and duration of your highs and lows.
Take your meds
Whether you have type 1 or type 2 diabetes, it is vitally important to take your diabetes medications as prescribed and on time. With so many factors affecting glucose that are beyond our control, taking medications in a consistent, timely manner is something that is completely within your control … and a real difference-maker for improving TIR.
Those who require multiple doses of insulin daily can benefit from the latest “hybrid closed-loop” (HCL) technology. These systems automatically adjust a pump’s insulin delivery based on current glucose values and trends. This 24-hour automated “assistance” reduces the work/responsibilities of the user while promoting greater TIR.
Adjust, adjust, adjust
Many people define insanity as doing the same thing twice and expecting different results. Insanity is no way to achieve a desirable TIR! If something is not working, do something about it. Not that occasional out-of-range readings are unacceptable, but patterns of out-of-range readings are something that should be acted on. Communicate with your health care team, and ask them for guidelines to follow so that you can make your own adjustments.
Adapt to the situation
Life is all about change. It would be nice if we could all live under perfectly ideal conditions all the time, but things happen! Stress, illness, injury, travel, restaurant meals, changes in physical activity, new medications, and visits from your in-laws represent recurring events that can pose obstacles to glucose management and lessen TIR. Don’t just accept it! Use your diabetes management tools and skills to improve your glucose management in these and other challenging situations.
Even though change is perfectly normal, one’s usual day-to-day lifestyle can greatly influence TIR. Sticking to a reasonably consistent schedule for things like meals, exercise, and sleep can go a long way towards producing more consistent and predictable glucose levels.
Small changes add up
So, there you have it. Think of TIR as a “new and improved” version of the A1C, providing insight into the true quality of your glucose control. Determine a reasonable target range for yourself, and apply strategies for improving your TIR. With more TIR, you’ll likely find yourself feeling better and performing better in many aspects of your life, all while helping to prevent long-term health problems. Regardless of where you’re starting, challenge yourself to do better! Over time, small improvements can really add up.
Want to learn more about blood glucose management? See our “Blood Sugar Chart,” then read “Blood Sugar Monitoring: When to Check and Why,” “Strike the Spike II: How to Manage High Blood Glucose After Meals,” and “Five Hacks to Help Control Blood Sugar Naturally.”