CGM & Time in Range
Continuous glucose monitors (CGM), as the name suggests, continually monitor the glucose (sugar) in your blood through an external device that’s attached to your body, and gives real-time updates. They’ve become popular and more accurate over the years, and with that improvement has come a new way to manage your blood glucose—enter time in range (TIR).
What is time in range?
Time in range is the amount of time you spend in the target blood glucose (blood sugar) range—between 70 and 180 mg/dL for most people.
The time in range method works with your CGM’s data by looking at the amount of time your blood glucose has been in target range and the times you’ve been high (hyperglycemia) or low (hypoglycemia). Time in range is often depicted as a bar graph showing the percentage of time over a specific amount of time when your blood glucose was low, in range, and high. This data is helpful in finding out which types of foods and what activity level causes your blood glucose to rise and fall.
Most people with type 1 and type 2 diabetes should aim for a time in range of at least 70 percent of readings—meaning 70 percent of readings, you should aim for roughly 17 out of 24 hours each day to be in range (not high or low). Some may have different targets. Talk with your doctor to figure out the right blood glucose levels and time in range targets are right for you.
What does the research say?
Because CGMs are relatively new, we’re still learning about the long-term results of time in range. Here’s what we do know: the more time you spend in range, the less likely you are to develop certain diabetes complications. However, a lot more research needs to be done. What we understand about the link between time in range and diabetes complications comes from data before CGMs were in use. The good news is, as more people start using CGMs, we anticipate more data for research will be collected and more information will be available for the long-term effect of spending more time in your target range.
Time in range versus A1C
A1C is a measure of your average blood glucose for the previous three months—but it doesn’t document the daily highs and lows that people may have. The introduction of time in range is a result of the improvements in diabetes management (specifically CGMs) and what we find out from your A1C, the current gold standard for determining diabetes management.
Without knowing the details of your highs and lows, your doctor might prescribe medication in a dose that lowers your blood glucose into hypoglycemia territory, creating a situation where you need to correct medications over time. Being able to know your average blood glucose levels as well as the highs and lows time in range provides a bigger picture of what’s needed to manage your diabetes.
Does that mean A1C is on the way out? No. It has been and likely will remain the standard measure of diabetes management because it’s well established that A1C can be used to predict and help prevent diabetes complications.
Who should use time in range?
People with type 1 diabetes and those with type 2 who use insulin and have tight blood glucose goals will benefit the most from reviewing their time in range data. That’s because they’re most likely to have blood glucose levels outside their target range.
Research has yet to establish how often people should check their time in range status. However, many people with diabetes find daily and weekly summaries to be helpful. The more times you check your blood glucose levels each day, the more you’ll know about how long you are in range.
If you have type 2 diabetes, but do not use insulin, your health care provider may still advise you to use a CGM periodically to measure how much time your glucose is in range.
Still interested in understanding your time in range? Talk to your doctor about using a professional CGM for about two weeks to figure out your time in range patterns. Your doctor may recommend that you do this to confirm that your time in range since it gives more information than standard blood glucose meters.
One barrier to the widespread use of time in range for diabetes management is the limited number of people who use a CGM. Though the numbers have dramatically increased in recent years, we still believe a minority of people with diabetes are using one.
With insurance coverage of CGMs improving and with Medicare covering CGMs for anyone who uses an insulin pump, injects insulin multiple times a day, or checks their blood glucose at least four times a day—there will likely be more and more people who begin to use them.
At the end of the day though, time in range data is meaningless unless both patients and their diabetes care team take the time to check it.
As for what time in range target you should aim for, remember: there’s no universal time in range goal. Yours will depend on your diabetes management needs and lifestyle, and your doctor can help you determine the right range for you.