Living with diabetes has its ups and downs, especially when it comes to blood glucose. For years, the hemoglobin A1C has been the gold standard for providing an overview of average glucose values from the previous two to three months. But now there is a new measurement in town — time in range (TIR). TIR comes from the data provided by CGMs (continuous glucose monitors). These devices are able to obtain a glucose value every five minutes via a sensor worn on the body that transmits the information to a smartphone or personal device manager (PDM). There are currently four companies offering CGM systems in the United States:
Abbott (FreeStyle Libre 3, FreeStyle Libre 2, FreeStyle Libre 14 Day)
Dexcom (Dexcom G7, Dexcom G6)
Medtronic (Guardian Connect)
Research has found that having a TIR (with the range defined as 70-180 mg/dl) at or above 70% is recommended for reducing the incidence of diabetes-related complications. For most people, readings lower than 70 mg/dl and above 180 mg/dl should be minimized. (Speak with your provider about your personal target range.) Take this quiz to see how much you know about TIR.
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1. If I have access to my TIR data, then I don’t need to get my A1C checked.
2. Having glucose values that are above 180 mg/dl is always safer than those below 70 mg/dl.
3. My blood glucose level on my meter does not match the reading on my CGM. Which is accurate?
4. If I don’t have a CGM, I can’t determine my TIR.
1. False. For many years, hemoglobin A1C has been the gold standard for evaluating average glucose values over the preceding two to three months. On the other hand, the concept of TIR is still very new, and not all health care professionals are aware of this metric or how it can be beneficial for guiding treatment. Adoption of new technology is sometimes slow in health care, so providers will continue to use the A1C until another option is widely available. And for now, many medical professionals will look at both measures to optimize treatment.
2. False. Episodes of severe hypoglycemia (low blood glucose) are associated with a variety of dangerous consequences, including seizures and loss of consciousness. However, high glucose values can also, over time, lead to a variety of diabetes complications that affect multiple parts of the body, including neuropathy (nerve damage), nephropathy (kidney damage), retinopathy (eye damage), cardiovascular conditions, and more. High blood glucose can also result in potentially life-threatening situations known as diabetic ketoacidosis (DKA, which is characterized by high blood glucose and levels of substances of known as ketones in the blood and urine) and hyperglycemic hyperosmolar syndrome (HHS, which is characterized by high blood glucose and severe dehydration). Therefore, both high and low glucose values can potentially be dangerous, which is why maintaining a TIR at or above 70% is so beneficial.
3. C. The simple answer is that both are likely accurate. This is because a meter relies on readings from blood to calculate the glucose values, while a CGM calculates the values using interstitial fluid (fluid under the skin that surrounds the cells). With that being said, if both devices are functioning properly, the readings on your meter and CGM should be within 20% of each another.
4. True. A CGM will produce a new reading every five minutes, but people do not do finger-stick checks with a meter every five minutes to obtain comparable data. If you monitor numerous times per day, you could theoretically calculate the percentage of readings that were in your target range, but this information would not be nearly as accurate as calculations made with the data provided by a CGM. To learn more about TIR, visit bit.ly/3JUxrjH or doi.org/10.2337/ds20-0093.
Want to learn more about time in range? Read “Diabetes: Time In Range.”