CBG Monitoring Targets for Insulin-Controlled Diabetes
For patients on insulin therapy, glucose control is considered adequate when capillary blood glucose (CBG) readings consistently fall within 100-180 mg/dL (5.6-10 mmol/L) before meals and at bedtime, with HbA1c ≤7% for most adults, while avoiding hypoglycemia (<70 mg/dL or 3.9 mmol/L). 1, 2
Monitoring Frequency and Timing
For patients on intensive insulin regimens (multiple daily injections or insulin pump therapy), CBG monitoring should occur at specific times 1:
- Before each meal and snacks
- At bedtime
- Occasionally postprandially (1-2 hours after meals)
- Prior to exercise
- When hypoglycemia is suspected
- After treating hypoglycemia until normoglycemic
- Before critical tasks (e.g., driving)
- During the night (3 AM) if nocturnal hypoglycemia is suspected 3
This typically requires 6-10 CBG checks daily, though individual needs vary 1, 2, 1.
Target Ranges Indicating Control
Primary targets 2:
- Fasting/preprandial glucose: 80-130 mg/dL (4.4-7.2 mmol/L)
- General target range: 100-180 mg/dL (5.6-10 mmol/L)
- Upper limit: <180 mg/dL (<10 mmol/L)
- Hypoglycemia threshold: <70 mg/dL (<3.9 mmol/L) should be avoided
Time-in-range metrics (when using continuous monitoring for comparison):
- >70% of readings should fall within 100-180 mg/dL 4
- <4% of time below 70 mg/dL 5
- <25% of time above 180 mg/dL 5
Assessing Overall Control
Beyond individual readings, control is evaluated through 1, 5:
- HbA1c levels: Target ≤7% for most adults (individualized based on age, comorbidities, hypoglycemia risk)
- Pattern analysis: Review CBG data over 1-2 weeks to identify trends by time-of-day
- Hypoglycemia frequency: Minimal episodes, especially severe hypoglycemia requiring assistance
- Glucose variability: Coefficient of variation <36% indicates stable control 4
Critical Monitoring Considerations
Common pitfalls to avoid 1, 2:
- Meter accuracy: Use only FDA-approved meters with unexpired strips from licensed distributors
- Technique errors: Ensure proper handwashing, avoid excessive finger squeezing, use fresh lancets 6
- Interfering substances: High-dose vitamin C, acetaminophen, and hypoxemia can affect accuracy 1, 2
- Timing specificity: Different insulin types cause hypoglycemia at different times—basal insulin and sulfonylureas predominantly cause nocturnal hypoglycemia (midnight-8 AM), while premixed insulin causes evening hypoglycemia (4 PM-midnight) 3
When Control is NOT Adequate
Indicators requiring insulin adjustment 1, 7:
- Persistent hyperglycemia: Fasting glucose consistently >130 mg/dL or random >180 mg/dL
- Recurrent hypoglycemia: Multiple episodes <70 mg/dL, especially if asymptomatic or nocturnal
- High glucose variability: Wide swings between high and low readings
- HbA1c above target despite monitoring
- Unexplained discrepancies between HbA1c and CBG patterns
Structured Monitoring Approach
For basal insulin users 1: Focus on fasting glucose measurements to guide dose titration, aiming for fasting glucose 80-130 mg/dL.
For basal-bolus regimens 1: Use preprandial readings to adjust mealtime insulin doses and bedtime readings to adjust basal insulin.
Documentation strategy 7: Record diet, exercise, medication timing, and glucose-related events alongside CBG readings to identify patterns and guide adjustments.
The key principle is that performing CBG monitoring alone does not improve control—the data must be actively used to adjust insulin doses, dietary intake, and physical activity 1. Patients require ongoing education on interpreting results and making appropriate therapeutic adjustments, with regular provider review of technique and data utilization.