What is the ideal blood sugar data set from Continuous Glucose Monitoring (CGM) data?

Ideal CGM Data Set for Blood Sugar Monitoring

For most adults with diabetes, the ideal CGM data set should include >70% time in range (70-180 mg/dL) with <4% time below range (<70 mg/dL) and <25% time above range (>180 mg/dL), measured over at least 14 days with ≥70% active CGM wear time. 1

Core CGM Metrics for Optimal Blood Sugar Management

Data Collection Requirements

• Minimum 14 days of CGM wear for reliable assessment of glycemic patterns 1
• At least 70% active CGM time (approximately 10 days of data) to ensure accurate representation of glycemic status 1

Essential Metrics for Comprehensive Assessment

1. Mean glucose - provides overall average 1
2. Glucose Management Indicator (GMI) - calculated value approximating A1C 1
3. Glycemic variability - target coefficient of variation (CV) ≤36% 1
   • Some studies suggest lower CV targets (<33%) provide additional protection against hypoglycemia for those on insulin or sulfonylureas 1

Time in Ranges (Key Targets)

• Time in Range (TIR): >70% of readings between 70-180 mg/dL (3.9-10.0 mmol/L) 1

  • Each incremental 5% increase in TIR is associated with clinically significant benefits 1
  • For young people (<25 years) with A1C goal of 7.5%, TIR target may be adjusted to approximately 60% 1

• Time Below Range (TBR):

  • Level 1 (54-69 mg/dL): <4% of readings 1
  • Level 2 (<54 mg/dL): <1% of readings 1

• Time Above Range (TAR):

  • Level 1 (181-250 mg/dL): part of the <25% total time above range 1
  • Level 2 (>250 mg/dL): minimize as much as possible 1

Modified Targets for Special Populations

Older Adults/High-Risk Individuals

• TIR: >50% (≥12 hours/day) in range 70-180 mg/dL 1
• TBR: <1% (<15 min/day) below 70 mg/dL 1
• TAR: <10% (<2 hours, 24 min/day) above 250 mg/dL 1

Pregnancy

• Target range: 63-140 mg/dL (3.5-7.8 mmol/L) 1
• Specific TIR targets differ from non-pregnant individuals 1

Visualization and Reporting

• Standardized single-page glucose reports with visual cues such as the Ambulatory Glucose Profile (AGP) should be used 1
• Reports should include all 10 standardized CGM metrics for comprehensive assessment 1

Clinical Context and Interpretation

• CGM data provides more actionable information than A1C alone, which only reflects average glucose over 2-3 months 1
• A1C can be affected by conditions such as anemia, hemoglobinopathies, and pregnancy, making CGM data particularly valuable 1
• For comparison, healthy non-diabetic individuals typically spend:
  • 96% of time between 70-140 mg/dL 2
  • Only about 1.1% of time below 70 mg/dL 2
  • Only about 2.1% of time above 140 mg/dL 2

Common Pitfalls to Avoid

• Insufficient data collection: Less than 14 days or <70% active time may not provide reliable assessment 1
• Focusing only on mean glucose: Missing important patterns of hypoglycemia or hyperglycemia 1, 3
• Ignoring glycemic variability: CV >36% indicates unstable glucose levels with higher risk of hypoglycemia 1
• Setting unrealistic targets: Goals should be adjusted based on age, comorbidities, and hypoglycemia risk 1

Remember that structured, consistent use of glucose data leads to improvements in glycemic control regardless of whether using CGM or traditional blood glucose monitoring, though CGM is more effective at minimizing hypoglycemia, particularly for those on higher-risk medications 4.