Safe Glucose Range for Diabetic Patients on CGM
For most adults with diabetes using continuous glucose monitoring, the safe target range is 70-180 mg/dL (3.9-10.0 mmol/L), with a goal of spending more than 70% of time in this range while keeping time below 70 mg/dL to less than 4%. 1, 2
Core Target Ranges
The American Diabetes Association has established standardized CGM metrics that define safe glucose parameters:
- Time in Range (TIR): >70% of readings between 70-180 mg/dL (3.9-10.0 mmol/L) 1, 2, 3
- Time Below Range (TBR): <4% total time below 70 mg/dL, with <1% below 54 mg/dL 1, 2
- Time Above Range (TAR): <25% total time above 180 mg/dL 2, 4
Each 5% increase in time in range provides clinically meaningful benefits, making incremental improvements toward the 70% target worthwhile 2, 4.
Hypoglycemia Thresholds (Critical Safety Limits)
Understanding hypoglycemia levels is essential for preventing dangerous glucose drops:
- Level 1 Hypoglycemia: 54-69 mg/dL (3.0-3.8 mmol/L) - requires immediate action 1, 3
- Level 2 Hypoglycemia: <54 mg/dL (<3.0 mmol/L) - clinically significant, dangerous hypoglycemia 1, 3
The priority in hospital settings and high-risk situations is hypoglycemia prevention, keeping time below 70 mg/dL at <1% 5.
Hyperglycemia Thresholds
Elevated glucose is categorized into two levels:
- Level 1 Hyperglycemia: 181-250 mg/dL (10.1-13.9 mmol/L) 1
- Level 2 Hyperglycemia: >250 mg/dL (>13.9 mmol/L) - should be minimized as much as possible 1, 2
Additional Safety Metrics
Beyond time in range, glycemic variability matters for safety:
- Coefficient of Variation (CV): Target ≤36%, though some evidence suggests <33% provides additional hypoglycemia protection for insulin-treated patients 1, 2, 3
- Mean Glucose: Should correlate with target A1C goals, typically corresponding to approximately 154 mg/dL for a 7% A1C 6
Modified Targets for Special Populations
Advanced Chronic Kidney Disease/Dialysis Patients
Given the heightened hypoglycemia risk from impaired kidney gluconeogenesis and decreased insulin clearance, more conservative targets apply:
Older Adults and High-Risk Individuals
The American Diabetes Association recommends:
- TIR: >50% (≥12 hours/day) in range 70-180 mg/dL 2
- TBR: <1% (<15 minutes/day) below 70 mg/dL 2
- TAR: <10% (<2 hours, 24 minutes/day) above 250 mg/dL 2
Children and Adolescents
While the standard 70-180 mg/dL range applies, targets should account for hypoglycemia unawareness risk and developmental factors 1. Less stringent A1C goals (such as <7.5% or <8%) may be appropriate for those with frequent hypoglycemia or limited access to technology 1.
Data Collection Requirements
For reliable CGM assessment:
- Minimum monitoring duration: 14 days 1, 2, 3
- Active CGM time: ≥70% of the 14-day period (approximately 10 days of data) 1, 2
Without adequate data collection, CGM metrics may not accurately represent glycemic patterns 2.
Clinical Context: Why These Ranges Matter
The 70-180 mg/dL target range balances microvascular complication prevention (achieved through lower glucose levels) against hypoglycemia risk 1. Time in range correlates moderately with A1C (correlation ~0.7), with approximately 70% TIR corresponding to an A1C of 7%, and 50% TIR corresponding to an A1C of 8% 6. However, for any given TIR percentage, there exists a wide range of possible A1C values, making CGM data more actionable than A1C alone 6.
Common Pitfalls to Avoid
- Focusing solely on mean glucose while ignoring time below range can miss dangerous hypoglycemic episodes 2
- Insufficient data collection (less than 14 days or <70% active time) leads to unreliable assessments 2
- Ignoring glycemic variability (CV >36%) increases hypoglycemia risk even when mean glucose appears acceptable 2
- Setting unrealistic targets for high-risk populations increases treatment burden without improving outcomes 2
Priority Hierarchy for Safety
When managing CGM data, prioritize in this order: