What are the target blood glucose levels for normal Continuous Blood Glucose (CBG) monitoring trends in individuals with diabetes?

Normal CGM Monitoring Trends: Target Blood Glucose Levels

For most nonpregnant adults with diabetes, the target is to maintain Time in Range (TIR) >70% (glucose 70-180 mg/dL or 3.9-10.0 mmol/L), with Time Below Range <4% and Time <54 mg/dL <1%. 1

Core CGM Metrics and Targets

Time in Range (TIR) Goals

• Standard target for most adults: >70% of readings between 70-180 mg/dL (3.9-10.0 mmol/L), which translates to >16 hours and 48 minutes per day 1
• Older adults or high-risk individuals: >50% TIR (>12 hours per day) with more relaxed targets to minimize hypoglycemia risk 1
• Each 5% increase in TIR provides clinically significant benefits for reducing microvascular complications 1

Time Below Range (TBR) - Hypoglycemia Prevention

• Level 1 hypoglycemia (54-69 mg/dL): <4% of time (<1 hour per day) for most adults 1
• Level 2 hypoglycemia (<54 mg/dL): <1% of time (<15 minutes per day) for all adults 1
• High-risk/older adults: Combined TBR <1% (<15 minutes per day) to prioritize safety 1

Time Above Range (TAR) - Hyperglycemia Limits

• Level 1 hyperglycemia (181-250 mg/dL): <25% of time (<6 hours per day) for most adults 1
• Level 2 hyperglycemia (>250 mg/dL): <5% of time (<1 hour 12 minutes per day) for most adults 1
• Older adults: Combined TAR <50% (<12 hours per day), with Level 2 <10% 1

Glycemic Variability

• Coefficient of variation (%CV): Target ≤36% to minimize dangerous glucose fluctuations 1
• Some evidence suggests targeting <33% provides additional protection against hypoglycemia for those on insulin or sulfonylureas 1

Data Collection Requirements

Minimum Monitoring Duration

• 14 days of CGM wear is required for pattern management and accurate assessment 1
• 70% active CGM time over those 14 days strongly correlates with 3-month mean glucose and time in range metrics 1
• For CGM use between 45-95% over 90 days, 14 days minimum sampling is sufficient for mean glucose, TIR, and TAR metrics 2
• Assessment of hypoglycemia requires longer sampling: 28-35 days for time <54 mg/dL regardless of CGM use frequency 2

Special Population Targets

Advanced Chronic Kidney Disease/ESKD

• TIR target: >50% (more conservative due to heightened hypoglycemia risk from impaired kidney gluconeogenesis and decreased insulin clearance) 1
• TBR target: <1% (stricter hypoglycemia prevention given increased risk) 1
• Use Glucose Management Indicator (GMI) instead of HbA1c when discordance exists, as HbA1c has low accuracy in advanced CKD 1

Hospitalized Patients

• Target range: 70-180 mg/dL with priority on hypoglycemia prevention 3
• Keep time <70 mg/dL at <1%, with heightened awareness when glucose is 72-106 mg/dL, especially with downward CGM trend arrows 3
• While 70% TIR is ideal, hypoglycemia prevention takes priority during acute illness 3

Pregnancy and Gestational Diabetes

• Tighter target range: 63-140 mg/dL (3.5-7.8 mmol/L) instead of the standard 70-180 mg/dL 1
• More stringent monitoring required with specific postprandial targets 4

Practical Implementation Algorithm

Step 1: Verify Adequate Data Collection

• Confirm ≥14 days of CGM data with ≥70% active time before making treatment decisions 1
• If assessing hypoglycemia patterns, extend to 28-35 days of data collection 2

Step 2: Assess Primary Metrics in Order

1. First priority - Safety: Check TBR <54 mg/dL is <1% and TBR 54-69 mg/dL is <4% 1
2. Second priority - Efficacy: Verify TIR 70-180 mg/dL is >70% (or >50% for high-risk patients) 1
3. Third priority - Variability: Confirm %CV is ≤36% 1
4. Fourth priority - Hyperglycemia: Check TAR >250 mg/dL is <5% and TAR 181-250 mg/dL is <25% 1

Step 3: Use Ambulatory Glucose Profile (AGP) for Pattern Recognition

• Standardized single-page AGP reports with visual cues showing median (50th percentile) and interquartile ranges (25th-75th percentiles) should guide treatment adjustments 1
• AGP displays glucose patterns as if occurring in a single day, making it easier to identify timing of hyperglycemia or hypoglycemia 1

Critical Pitfalls to Avoid

Don't Ignore Hypoglycemia Despite Good TIR

• Even individuals with low TBR percentages can experience substantial numbers of severe hypoglycemic events 1
• Monitor frequency of hypoglycemic events separately, not just percentage of time below range 1

Don't Accept Suboptimal CGM Use Without Adjustment

• For CGM use <70%, recognize that 14 days may not adequately capture hypoglycemia patterns, requiring 28-35 days of data 2
• Coefficient of variation requires 28 days of sampling regardless of CGM use percentage 2

Don't Apply Standard Targets to All Populations

• Patients with advanced CKD require more conservative TIR targets (>50% vs >70%) due to altered glucose metabolism and increased hypoglycemia risk 1
• Older adults with frailty should target >50% TIR with <1% combined TBR to prioritize safety over tight control 1

Don't Rely on Mean Glucose or GMI Alone

• While mean glucose and GMI provide useful averages, they miss critical information about time spent in hypoglycemia and hyperglycemia ranges 1
• A patient can have acceptable mean glucose but dangerous glycemic variability with significant time in both hypo- and hyperglycemia 1

Don't Forget to Adjust for Real-World Achievability

• Research shows that even patients achieving HbA1c <7.5% only maintain approximately 60% of readings in target range (72-180 mg/dL), with up to 30% of readings >180 mg/dL being common 5
• This suggests the 70% TIR target, while evidence-based, represents optimal rather than typical control 5