Time in tight range (TITR): emerging evidence and clinical perspectives

Continuous glucose monitoring (CGM) has enabled increasingly stringent assessment of glycemic control beyond conventional time in range (TIR; 70-180 mg/dL). Time in tight range (TITR), defined as the percentage of time with glucose levels between 70 and 140 mg/dL, was proposed in 2023 as a more stringent CGM-derived metric. This review summarizes current evidence regarding the clinical significance and limitations of TITR. TITR correlates strongly with HbA1c and TIR, and may be more sensitive than TIR to changes in mean glucose when glycemia approaches the normal range. Recent cohort studies suggest that lower TITR is linearly associated with higher risks of all-cause and cardiovascular mortality, while higher TITR is associated with lower incidence of diabetic retinopathy. TITR has also shown associations with favorable outcomes in COVID-19 pneumonia. However, its interpretation requires caution because glycemic variability can influence TITR differently according to mean glucose levels. In individuals with type 1 diabetes treated with multiple daily injections, higher TITR may be accompanied by increased time below range, suggesting that indiscriminate pursuit of higher TITR could increase hypoglycemia risk. Further prospective studies are needed to establish optimal TITR targets and determine whether TITR provides prognostic value beyond established CGM metrics across diverse populations.