What Is a Continuous Glucose Monitor (CGM)?
A Continuous Glucose Monitor (CGM) is a wearable device that tracks your blood glucose levels 24/7, providing real-time data without the need for finger pricks. Unlike traditional blood glucose meters that offer a single snapshot in time, CGMs provide a comprehensive view of how your glucose levels change throughout the day and night.
Key Components:
- •Sensor: A tiny filament inserted just under the skin that measures glucose in interstitial fluid
- •Transmitter: Sends glucose data wirelessly to a receiver or smartphone
- •Display Device: Shows real-time glucose readings, trends, and alerts
How CGMs Work
CGMs work by measuring glucose levels in the interstitial fluid—the fluid surrounding your body's cells. Here's the process:
Measurement
A tiny sensor measures glucose in interstitial fluid every 1-5 minutes
Transmission
Data is wirelessly transmitted to your smartphone or receiver
Display
Current glucose level, trend arrows, and historical data are displayed in real-time
Alerts
Customizable alarms warn you of high or low glucose levels
Important: Interstitial glucose readings lag behind blood glucose by 5-15 minutes, which is why you should still use fingerstick testing for calibration (some models) and treatment decisions during rapid changes.
Benefits of Using a CGM
CGMs offer significant advantages over traditional blood glucose monitoring:
No More Finger Pricks
Eliminate the need for painful fingerstick tests throughout the day (though some models require occasional calibration)
Continuous Monitoring
Track glucose levels 24/7, including during sleep—catching dangerous nighttime lows or highs
Trend Data & Predictions
See not just your current number, but which direction your glucose is heading and how fast
Customizable Alerts
Receive warnings before dangerous highs or lows occur, giving you time to take action
Pattern Recognition
Identify how different foods, activities, stress, and medications affect your glucose levels
Better A1c Control
Studies show CGM users achieve 0.3-1.0% lower A1c levels compared to fingerstick-only monitoring
Top CGM Devices in 2025
Here's a detailed comparison of the leading CGM systems available in 2025:
| Feature | Dexcom G7 | Freestyle Libre 3 | Guardian 4 |
|---|---|---|---|
| FDA Approval | Type 1 & 2 (Age 2+) | Type 1 & 2 (Age 4+) | Type 1 (Age 7+) |
| Sensor Duration | 10 days | 14 days | 7 days |
| Warm-up Time | 30 minutes | 60 minutes | 2 hours |
| Calibration Required | No | No | Yes (2-4x daily) |
| Reading Frequency | Every 5 min | Every 1 min | Every 5 min |
| Smartphone App | iOS & Android | iOS & Android | iOS & Android |
| Share Features | Up to 10 followers | Up to 20 followers | Limited sharing |
| Estimated Cost/Month | $300-350 | $75-150 | $250-300 |
Best Overall: Dexcom G7
Most accurate, fastest warm-up, excellent app, robust sharing features. Premium price but worth it for comprehensive monitoring.
Best Value: Freestyle Libre 3
Longest sensor life, most frequent readings, most affordable option. Great for those on a budget or without insurance coverage.
Best for Insulin Pump Users: Guardian 4
Integrates seamlessly with Medtronic insulin pumps for automated insulin delivery. Requires calibration but offers tight integration with pump therapy.
Cost & Insurance Coverage
CGM costs can be significant, but insurance coverage is increasingly common:
Typical Out-of-Pocket Costs:
Insurance Tips:
- • Medicare covers CGMs for insulin users with diabetes
- • Many private insurers cover CGMs as durable medical equipment
- • Prior authorization may be required—work with your doctor
- • FSA/HSA funds can be used for CGM expenses
- • Manufacturer discount programs can reduce costs significantly
Who Should Use a CGM?
While CGMs were originally designed for people with Type 1 diabetes, they're now beneficial for a much wider range of individuals:
Highly Recommended For:
- • Type 1 diabetes
- • Type 2 diabetes on insulin
- • Frequent hypoglycemia episodes
- • Hypoglycemia unawareness
- • Pregnant women with diabetes
- • A1c above 7% despite treatment
May Benefit:
- • Prediabetes
- • Type 2 diabetes (non-insulin)
- • Athletes optimizing performance
- • Individuals focused on metabolic health
- • Those with reactive hypoglycemia
- • People with PCOS
Getting Started with a CGM
Ready to start CGM monitoring? Here's the process:
Talk to Your Doctor
Discuss whether a CGM is right for you and get a prescription if needed. Your doctor can help with insurance pre-authorization.
Choose Your Device
Research the options above and consider your lifestyle, budget, and specific needs.
Order & Set Up
Order through your pharmacy or directly from the manufacturer. Download the app and follow setup instructions.
Apply Your First Sensor
Follow manufacturer instructions for sensor placement (usually upper arm or abdomen). Most sensors are painless to apply with an applicator.
Learn Your Patterns
Spend 1-2 weeks observing how your glucose responds to meals, exercise, stress, and sleep. Use this data to make informed decisions.
The Bottom Line
Continuous Glucose Monitors represent a revolutionary advancement in diabetes management and metabolic health tracking. The real-time data, trend insights, and alerts provide an unprecedented level of control and understanding of your glucose levels.
Whether you have Type 1 diabetes, Type 2 diabetes, or simply want to optimize your metabolic health, a CGM can provide invaluable insights that lead to better outcomes and quality of life. While the upfront cost may seem significant, the long-term benefits in health outcomes and peace of mind are often worth the investment.
Ready to Explore CGM Options?
Check out our in-depth reviews and comparisons of the top CGM devices available in 2025.
View Device Reviews