What is time-in-range (TIR) in CGM monitoring and why is it important?

• A. The percentage of time glucose stays within target range (e.g., 70-180 mg/dL); associated with reduced complications and better control.
• B. The average glucose level over 24 hours; correlates with HbA1c.
• C. The number of days with glucose outside range; predicts hypoglycemia risk.
• D. The time spent fasting; used to adjust meal timing.

Answer: (A)

Time-in-range in CGM monitoring is the percentage of time glucose readings stay within a defined target window, commonly about 70–180 mg/dL for many adults with diabetes. This measure matters because it shows how consistently glucose stays in a safe, desirable range, not just what the average looks like. You can have a decent overall average yet still spend a lot of time riding high after meals or dipping low at night; time-in-range reveals those fluctuations. Clinically, higher time-in-range is linked with lower risk of complications and reflects better day-to-day control. It also complements HbA1c by capturing variability and hypoglycemia risk, helping patients and clinicians tailor insulin dosing, meal timing, and activity to keep glucose within target more often. Other metrics describe different ideas—average glucose over 24 hours relates to HbA1c but misses fluctuations; counting days outside range isn’t about the proportion of time in range; and time spent fasting is not what CGM-time-in-range measures.