What is time above range (TAR) in continuous glucose monitoring (CGM)?

Time Above Range (TAR) in Continuous Glucose Monitoring

Time Above Range (TAR) represents the proportion of CGM readings—or the absolute time—that exceed the upper glucose target, reported as Level 1 (181–250 mg/dL) and Level 2 (>250 mg/dL). 1, 2

Core Definition and Measurement

• TAR is one of three core "time-in-range" metrics alongside Time-in-Range (TIR: 70–180 mg/dL) and Time-Below-Range (TBR: <70 mg/dL). 2
• TAR can be expressed either as a percentage of total CGM readings or as absolute hours per day. 2
• For adults with diabetes, a TAR <25% corresponds to <6 hours of hyperglycemia per day above 180 mg/dL. 1, 2

Two-Level Classification System

The international consensus stratifies hyperglycemia into two clinically distinct levels:

• Level 1 TAR (moderate hyperglycemia): 181–250 mg/dL (10.1–13.9 mmol/L). 1, 2
• Level 2 TAR (severe hyperglycemia): >250 mg/dL (>13.9 mmol/L). 1, 2

This two-tier system allows clinicians to distinguish between moderate postprandial excursions and sustained severe hyperglycemia that requires more aggressive intervention. 1

Data Requirements for Reliable Assessment

• A minimum of 14 days of CGM data with ≥70% sensor wear time is required; this duration correlates strongly with 3-month mean glucose and hyperglycemia metrics. 1, 2
• Longer CGM data collection periods (e.g., 4 weeks) may be required for individuals with more variable glycemic control. 1

Population-Specific Clinical Targets

Adults with Type 1 or Type 2 Diabetes

• Target TAR <25% of the day (i.e., <6 hours) above 180 mg/dL. 1, 2
• This target applies to both type 1 and type 2 diabetes in standard-risk adults. 1

Older or High-Risk Individuals

• Target TAR <10% of the day (i.e., <2 hours 24 minutes) above 250 mg/dL (Level 2 only). 1, 2
• This more lenient target reflects the need to prioritize hypoglycemia avoidance in frail or high-risk populations. 1

Pregnancy

• Target glucose range is 63–140 mg/dL; TAR is defined as time >140 mg/dL with stricter goals to reduce fetal risk. 1, 2

Clinical Significance and Outcomes

• Each 5% increase in TIR (and corresponding decrease in TAR) is linked to clinically meaningful reductions in diabetes-related complications for both type 1 and type 2 diabetes. 1, 2
• TAR correlates strongly with mean glucose (r = -0.790, p <0.001), providing real-time insight into hyperglycemic excursions beyond what HbA1c offers. 3
• TAR independently predicts TIR alongside TBR and HbA1c, making it essential for treatment optimization. 2, 3

Integration with Other CGM Metrics

TAR should never be interpreted in isolation but always alongside TIR, TBR, and glycemic variability (coefficient of variation, CV). 1, 2

Therapeutic Priorities

• The primary therapeutic priority is to reduce TBR to <4% (<1 hour/day) for most adults and <1% (<15 minutes/day) for older/high-risk individuals before aggressively targeting TAR. 2, 4
• After hypoglycemia is controlled, aim for TIR >70% and TAR <25% in standard-risk adults. 2
• Glycemic variability should be kept ≤36% when evaluating TAR and TIR, as high variability raises the risk of both hypo- and hyperglycemia. 1, 2

Common Pitfall

Changes in TIR are not associated with changes in TBR, so reducing TAR to increase TIR must not come at the expense of increased hypoglycemia. 4 This is particularly critical in older adults using automated insulin delivery systems, where TBR should be addressed independently of TIR. 4

Practical Clinical Application

• Visualize TAR using the Ambulatory Glucose Profile (AGP), which aggregates 14 days of CGM data and highlights periods of hyperglycemia needing intervention. 1, 2
• When Level 2 TAR (>250 mg/dL) is elevated, consider intensifying basal insulin, adding or up-titrating GLP-1 receptor agonists or SGLT2 inhibitors, or adjusting prandial insulin coverage. 2
• CGM-guided interventions focusing on food and lifestyle choices can reduce TAR from 53–55% at baseline to 21–30% at 3–6 months, even without medication changes. 5