How do I use continuous glucose monitoring (CGM) for diabetes management?

How to Use Continuous Glucose Monitoring for Diabetes Management

Continuous glucose monitoring (CGM) devices should be used as close to daily as possible for maximal benefit, with intermittently scanned CGM devices scanned at minimum once every 8 hours to effectively lower A1C levels and reduce hypoglycemia risk in diabetes management. 1

Types of CGM Devices

There are two basic types of CGM devices:

1. User-owned devices (for frequent/continuous use):

   • Real-time CGM (rtCGM): Measures and displays glucose levels continuously without prompting
   • Intermittently scanned CGM (isCGM): Measures glucose continuously but requires scanning for visualization and storage of values

2. Professional CGM devices (clinic-based):

   • Placed on patients in healthcare settings
   • Worn for a discrete period (typically 7-14 days)
   • Data may be blinded or visible to the wearer
   • Used to assess glycemic patterns and trends 1

Patient Selection for CGM

CGM is primarily recommended for:

• Patients with type 1 diabetes (children, adolescents, and adults) 1
• Patients with type 2 diabetes on intensive insulin therapy or experiencing significant glycemic variability 1, 2
• Individuals with problematic hypoglycemia, hypoglycemia unawareness, or recurrent hypoglycemic episodes 2
• Pregnant women with diabetes 1

CGM is generally not recommended for:

• Patients with type 2 diabetes treated with diet and/or oral agents alone 1
• Patients in intensive care settings 1
• Individuals unwilling to learn the basic mechanical skills of the equipment 1

Setting Up and Using CGM

Initial Setup

1. Ensure proper education and training on device use 1
2. Apply the sensor according to manufacturer instructions (typically on the back of the upper arm)
3. Allow the sensor to warm up (time varies by device)
4. For devices requiring calibration:
   • Use the same glucose meter and batch of test strips
   • Obtain capillary blood glucose at stable times (before meals, before bedtime)
   • Enter calibration values immediately after obtaining them 1

Daily Use

1. For rtCGM: Use as close to daily as possible for maximum benefit
2. For isCGM: Scan at minimum once every 8 hours 1
3. Record diet, exercise, medication, and other relevant events in detail 1
4. Review glucose trends and patterns regularly
5. Use CGM data to make informed decisions about food intake and insulin dosing 2

Interpreting CGM Data

Focus on these key metrics:

1. Time in Range (TIR): Percentage of time spent within target glucose range (70-180 mg/dL)
2. Time Below Range: Percentage of time spent below target glucose range
3. Glycemic Variability: Measure of glucose fluctuations throughout the day 2

Maintenance and Precautions

Device Maintenance

• Replace sensors according to manufacturer schedule (typically every 7-14 days)
• Ensure proper adhesion to skin
• Keep transmitter charged (if applicable)

Important Precautions

• Avoid exposure to strong magnetic fields (MRI)
• Some devices may not be water-resistant
• Be aware of potential interfering substances:
  • For glucose oxidase monitors: uric acid, galactose, xylose, acetaminophen, L-dopa, ascorbic acid
  • For glucose dehydrogenase monitors: icodextrin (used in peritoneal dialysis) 1
• Skin reactions (irritation or allergy) should be assessed and addressed 1

Validating CGM Data

For real-time CGM data to be considered valid:

1. The system should have been worn for at least 12 hours (initial readings may be inaccurate)
2. The system should be adequately calibrated (difference between CGM and meter glucose <15%)
3. There should be no false alarms 1

Follow-up and Optimization

1. Schedule follow-up within 2-4 weeks of initial prescription
2. Review data to adjust insulin regimen as needed
3. Assess adherence to sensor replacement schedule and proper scanning technique
4. Regular review of CGM data to evaluate effectiveness of treatment adjustments 2

Clinical Benefits

When used properly, CGM can:

• Lower A1C levels
• Reduce hypoglycemia risk
• Improve time in target range
• Provide immediate feedback on glucose trends
• Help identify patterns that may be missed with traditional monitoring 2, 3

By following these guidelines for CGM use, patients can effectively monitor and manage their glucose levels, potentially improving both clinical outcomes and quality of life.